Crystal Structure Transformations in Inorganic Sulfates, Phosphates, Perchlorates, and Chromates Based on the Literature up to 1974

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Crystal Structure Transformations

in Inorganic Sulfates, Phosphates, Perchlorates, and Chromates NATIONAL BUREAU OF STANDARDS

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t: dAso Crystal Structure Transformations RaS , |q-7f in Inorganic Sulfates, Phosphates, FJ^eDS Perchlorates, and Chromates

C. N. R. Rao and B. Prakash * • *

Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India

U.S. DEPARTMENT OF COMMERCE, Rogers C. B. Morton, Secretory

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Issued November 1975 Library of Congress Cataloging in Publication Data

Rao. Chintamani Nagesa Ramachandra. Crystal Structure Transformations in Inorganic Sulfates, Phos- phates. Perchlorates, and Chromates.

INat. Stand. Ref. Data Ser. ; NSRDS-NBS 56) "National Standard Reference Data System.” Supt. of Docs. No.: C 13.48:56 1. Crystals. 2. Phase Rule and Equilibrium. 3. Chemistry, In- organic. I. Prakash, Braham, 1912-joint author. II. Title. III. Series: United States. National Bureau of Standards. National Standard Reference Data Series; NSRDS-NBS 56. OC100.U573 No. 56 [QD921] 389\6'08s [548 .81] 75-619082

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III Preface

Earlier in this series, we presented critical reviews of phase transitions in binary halides

(NSRDS—NBS 41), transition metal oxides (NSRDS-NBS 49), and inorganic nitrites, nitrates, and carbonates (NSRDS-NBS 53). In this monograph, we review crystal structure transformations in inorganic sulfates, phosphates, perchlorates, and chromates based on the literature up to 1974.

A review on transition metal sulfides is due to appear in Progress in Solid State Chemistry (Vol. 10) this year. We believe that these five reviews would adequately cover most of the important facets of crystal structure transformations in inorganic solids and indicate the nature of problems in this area. These reviews could not have been prepared but for the support and encouragement of the National Bureau of Standards.

IV Contents Page

1. Introduction 1

2. Units, Symbols, and Abbreviations 1

3. The Sulfates 2 3.1. Alkali Metal Sulfates 2 3.2. Ammonium Sulfate 5 3.3. Alkaline Earth Metal Sulfates 7 3.4. Thallium Sulfate 8 3.5. Lead Sulfate 9 3.6. 3d Transition Metal Sulfates 9 3.7. 4d Transition Metal Sulfates 12 3.8. Rare Earth Sulfates 13 References 13

4. The Phosphates 16 References 21

5. The Perchlorates 22 References 26

6. The Chromates 26 References 28

Crystal Structure Transformations in Inorganic Sulfates, Phosphates, Perchlorates, and Chromates*

C. N. R. Raof and B. Prakash

Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India

Literature dealing with crystal structure transformations of simple inorganic sulfates, phosphates, perchlorates and chromates has been critically reviewed. Data on thermodynamic, crystallographic, spectroscopic, dielectric and other properties are given. Experimental techniques employed to obtain the data are indicated and comments on the data are made wherever necessary. All pertinent references to the published literature (up to 1974) are listed.

Key words: Chromates; crystal structure; crystal structure transformations; perchlorates; phase transformations; phosphates; sulfates; thermodynamic data; x-ray diffraction data.

1. Introduction reviewed in the literature [5, 6] and some aspects were briefly presented in our earlier publications The study of crystal structure transformations is from NSRDS-NBS [2, 3]. We shall, therefore, not of great importance in understanding the structure resort to any discussion of a general nature in this and properties of inorganic solids. As part of our review. The present review covers the material pub- programme in preparing critical reviews on the crys- lished in the literature up to 1974 and2 lists most of tal structure transformations of various types of the important references. All the available crystal inorganic solids, we have presently carried out a structure data of the different phases have been survey of the transformations of inorganic salts con- given. Results of studies employing a variety of taining tetrahedral oxy-anions such as sulfates, phos- methods and properties of solids are also presented. phates, perchlorates and chromates. This review is a sequel to our monograph on the crystal structure transformations in inorganic nitrites, nitrates and References 1 carbonates [l]- ^ earlier monographs we have Rao, C. N. R., Prakash. B. and Natarajan, presented the transformations in binary halides [2] [1] M., “Crystal Structure Transformations in Inorganic Nitrites, Nitrates, and transition metal oxides [3]. and Carbonates”, NSRD-NBS Monograph 53, 1975. Of the various systems reviewed in this article, [2] Rao, C. N. R. and Natarajan, M., “Crystal Structure Trans- on the crystal the most extensive studies have been formations in Binary Halides”, NSRDS-NBS Monograph structure transformations of inorganic sulfates. 41, 1972.

Accordingly, we have discussed this system at [3] Rao, C. N. R. and Subba Rao, G. V., “Transition Metal Oxides: Crystal Chemistry, Phase Transitions and Related length. Stern and Weise [4] have reviewed the high Aspects”, NSRDS-NBS Monograph 49, 1974. temperature properties and decomposition of inor- [4] Stern, K. H. and Weise, E. L., “High Temperature Properties ganic sulfates. In view of the limited information and Decomposition of Inorganic Salts”, Part 1, Sulfates,

available on the crystal structure transformations NSRDS-NBS Monograph 7, 1966. in inorganic phosphates, perchlorates and chro- [5] Rao, C. N. R. and Rao, K. J., Progress in Solid State Chem- mates, we have presented the available data in istry, Ed. H. Reiss, Vol. 4, Pergamon Press, Oxford, 1967. [6] Rao, C. N. R. (Ed.), “Modern Aspects of Solid State Chem- tabular form. istry”, Plenum Press, New York, 1970. The general theory and other aspects of phase transformations in inorganic solids have been 2. Units, Symbols, and Abbreviations

1 Figures in brackets indicate literature references which appear after each section. o 8 ‘Supported by the National Bureau of Standards through the Special International A = Angstrom (10~ cm) Ptogram Earlier publications Rao and coauthors on crystal structure (NBS-G-77). by bar = Unit of pressure = 10 6 dyn/cm =10 5 pascal transformations in this series are NSRDS-NBS 41, 49, and 53.

tTo whom all correspondence should be addressed. cal = Thermochemical calorie = 4.1840 Joule

1 C = Coulomb exception of lithium sulfate where the transforma- eV = Electron volt tion is from a monoclinic to a cubic structure, the Hz = Hertz (cycle/second) other alkali metal sulfates show transformations to O e = Oersted from an orthorhombic a hexagonal phase [3] X = Magnetic susceptibility and there is a progressive increase in transition e' = Dielectric constant temperature and decrease in heat of transformation e" = Dielectric loss as we go from sodium to cesium sulfate. In table A = Curie constant 1, we have summarized the data on the crystal a =Seebeck coefficient structure transformations of alkali metal sulfates. gives crystal P s = Spontaneous polarization Table 2 structure data on the various II Tc = Curie temperature phases. The — I phase transition in alkali metal Tn = Neel temperature sulfates seems to have features of both first and — second order transitions as revealed by the thermo- Tt Transition temperature T — Temperature in kelvin (K) dynamic and structural data as well as electrical conductivity A H tr = Enthalpy of transformation measurements [4].

AS tr = Entropy of transformation Some special features of the transitions in indi- 7 A7 = Thermal hysteresis vidual alkali metal sulfates are described in the AP = Volume change following paragraphs. tr = Z Number of molecules per unit cell Lithium sulfate. The value of AHtr in lithium DTA = Differential thermal analysis sulfate is very high compared to other alkali metal EPR = Electron paramagnetic resonance sulfates [7] and is even higher than the heat of

IR = Infrared fusion of Li 2 S0 4 . This abnormality is possibly NMR = Nuclear magnetic resonance due to the high degree of disorder in the high 6 TGA = Thermo-gravimetric analysis temperature phase [3]. Substitution by Li isotope

lowers the Tt by 0.7 K [24]. Bridgman [25] did not find any high pressure

3. The Sulfates transformation in Li 2 S0 4 up to 50 kbar. Pistorius [26] has, however, identified three new high pres- 3.1. Alkali Metal Sulfates sure forms III, IV, and V. The phase diagram of

All the alkali metal sulfates undergo reversible Li 2 S0 4 shows the triple points at the pressures and

polymorphic transformations [1, 2]. With the temperatures listed below:

Table 1 Crystal structure transformations of alkali metal sulfates

Sulfate Transformation Tt , K AH tr , kcal AS tr , cal References mol -1 mol -1 K -1

Li 2 S0 4 II — I 859 6.5 7.6 [3, 5-8]

Na 2 S0 4 V^IV 443 0.7 1.6 [5, 9-13] IV — III 458 III^I 515 1.8 3.5 I-+II 509 (on cooling)

k 2 so4 II— I 858 1.94 2.27 [5, 6, 14, 15]

Rb 2S0 4 II— I 930 0.35 [15-17]

2.11 [6]

Cs 2 S0 4 II— I 940 0.600 ±0.13 [6, 7, 15] 0.50 [6] 986 [18] 993 [16]

2 )

Table 2. Crystal structure data of alkali metal sulfates

Sulfate Crystal system Space group Z Cell dimensions References (phases 1 2 3 4 5 6

Li 2 S0 4

II (298 K) monoclinic P2,/a 4 a = 8.2390 A, [19] 6=4.9536 A, c =8.4737 A, j3= 107.98°

I cubic F23 or F43m 4 a = 7.07 A [3]

Na 2 S04

V (298 K) orthorhombic Df±Fddd 8 a = 5.863 A [9] 6 = 12.304 A c =9.821 A - I (514 K) hexagonal — a = 5.405 A [15] c = 7.215 A

k 2 so4

II (298 K) orthorhombic D^-Pmcn 4 0 = 5.772 A [20] 6 = 10.072 A c = 7.483 A - I (858 K) hexagonal — a — 5.85 A [15] c =8.03 A

Rb 2 S0 4

II (298 K) orthorhombic D^-Pmcn 4 a = 7.801 A [21] 6=5.965 A c = 10.416 A

I hexagonal D3 -P3ml 2 o = 6. 151 ±0.005 A d [22] c= 8.467 ± 0.003 A

Cs 2 S0 4

II (298 K) orthorhombic Dl®-Pmcn 4 a = 6.264 A [23] 6 = 10.95 A c = 8.242 A

I hexagonal 0 = 6.485 A [18] c =8.980 A

I/III/II 10.7 ±0.5 kbar 877 ±3 K Sodium sulfate. Na 2 S0 4 (IV), stable above 443 K

III/IV/II 14.8 ±0.5 kbar 871 ±3 K and below 458 K is monoclinic [9] . Above 458 K the

III/V/IV 20.1 ±0.7 kbar 943 ±4 K stable phase is Na 2 S0 4 (III). Frevel [30] found

I/V/III 21.5 ±0.8 kbar 986 ±6 K Na 2 S0 4 (III) to have an orthorhombic unit cell with o Lithium sulfate monohydrate shows endothermic space group Pbnn and dimensions a = 5.59 ± 0.02 A, = transformations at 443, 853, and 1133 K due to b = 8.93 ±0.02 A, c = 6.98 ±0.02 A and Z 4. dehydration, polymorphic transformation, and Dasgupta [31] has, however, reported that Na2 S0 4 fusion, respectively [27], the last two effects (III) is tetragonal and belongs to a space group being reproducible. The 853 K transformation is D,*2I42, Z — 16, a — 13.45 A and c = 7.879 A. akin to that in anhydrous Li 2 S0 4 with a AHtr of Fischmeister [15] has shown Na 2 S0 4 (III) to pos- -1 6531 cal mol [28]. DTA and x-ray diffraction sess an orthorhombic unit cell at room temperature studies by Gruver [29] confirm the reversible with cell dimensions close to those by Frevel [30]. phase transformation around 873 K with a AT Fischmeister has also reported the cell parameters of 30 K. for the metastable orthorhombic Na 2 S0 4 (II) to be

3 S

Pannetier and Gaultier a = 5.775 A, 6 = 10.073 A and c — 7.481 A at room Potassium sulfate. [42] reported expansion discontinuities at 533 in a temperature. DTA studies of Kreidl and Simon [32] K show only one high temperature transition (V—»I) and c parameters, at 633 K in a and 6 parameters at in a, b, and c parameters. These varia- a 511 K which occurs directly and reversibly in pres- and 733 K tions, however, did not affect the orthorhombic ence of water. According to Bird [33] the high tem-

structure of K 2 S0 4 . perature transition in dry Na 2 S 0 4 is irreversible.

K 2 S0 4 was found to undergo some changes at and Gregor have shown the V —* I transi- Rao [34] , 573, 623, 723 K, and possibly at 663 K [43-45]. tion to be reversible even in dry Na2S0 4 . Moreau Moreau [14] however, detected only two trans- [14] found only three of the five previously observed formations at 623 K and 723 K, respectively. The forms in his DTA and x-ray diffraction investigations electrical conductivity measurements of Ramasastry of Na 2 S0 4 . Dialatometric studies by Kracek and and Acharyulu show an anomaly at 678 K. Gibson [11] have given the volume changes in the [46] Watanabe et al. [47] have found the dielectric various transitions of Na2S0 4 as follows: V ^ IV, 3 - 3 - constant of K 2 S 0 4 to increase with increasing tem- +0.0005 cm g *; IV ^ III, —0.0034 cm g III ^ I, 3 -1 perature resulting in a maximum around 873 K. The +0.007 cm g . Kracek and Gibson point out that electric conductivity shows an onic behaviour above Na2S0 4 (II) has no region of stability at low tem- 740 K with an activation energy of 0.8 eV. On heat- peratures, but if the reaction I—» III is inhibited, the

ing K 2 S0 4 , significant changes of the relative I —> II transformation takes place reversibly at 3 -1 intensities of the diffuse and Laue maxima take 509 K with a volume decrease of 0.004 cm g . High place well the transition temperature temperature x-ray diffraction and thermographic below [48]. It seems that the transition is preceded by a pre- studies of Khlapova [35] reveal two hexagonal phases between 723 and 873 K. This supports transition in a broad temperature interval. Struc- tural changes observed are not caused by the Wyronboff [36] who had reported a high tempera- nuclei of the new phase, but by a structural inter- ture transition in Na2S0 4 around 773 K. Simanov mediate between the low and high temperature and Kirkina [37] have found a new orthorhombic modification. There is very little indication of the form of Na 2 S0 4 at 993 K. A departure from linearity pretransition effect in K immediately below in the enthalpy versus temperature curve above 2 S0 4 Tf, as shown by the calorimetric measurements of 837.4 K was observed by Popov and Ginzburg [38]. Dworkin and Bredig [49]. According to them A H The effect was more clear in their mean specific heat tT -1 -1 is 2020 + 80 cal mol and A is 2.3 cal mol versus temperature curve which was interpreted as tr -1 deg . evidence for yet another polymorphic transforma- Up to 1 kbar the results of Majumdar and Roy tion. High temperature specific heat investigations and Pistorius [50] are almost identical. The of Schmidt and Sokolov [39] showed an anomaly [45] transition fine rises linearly with pressure to 22.6 between 963 and 993 K, with a A Htr of 0.01 kcal -1 kbar and 1263 K where the slope undergoes a sharp mol . This transformation is given as Na2 S0 4 change. This change in slope indicates a splitting (I)-»S— Na 2 S0 4 . of the II/I phase boundary and the appearance of Bridgman [40J studied Na2 S0 4 at pressures up to K S0 (III). Pistorius and Rapoport confirm that 50 kbar and temperatures up to 448 K. He en- 2 4 (II) at 853 differs crystallographically countered sluggish transitions around 10 kbar and K 2 S0 4 K from the room temperature phase. They, however, 27 kbar, corresponding to V /III and III/ VI trans- do not observe the higher order transformations formations, respectively. High pressure DTA studies around 573, 623, and 723 K in the high pressure by Pistorius [41] up to 45 kbar and 723 K have DTA. revealed two new phases VII and VIII. The phase discontinuities observed in diagram shows the triple points at the pressures Rubidium sulfate. The the thermal coefficients of the lattice parameters and and temperatures indicated below: volume indicate the existence of two new low energy transitions around 648 K and 848 K and a very low energy transformation at 548 K besides the usual

V/IV/III 1.5 ± 1.5 kbar 446 + 13 K II ^ I transformation [51]. I/III/VII 13 ±1 kbar 603+ 8K Cesium sulfate. DTA, dilatometric and crystallo- III/VI/VII 22.5 + 1 kbar 548+ 8 K graphic investigations by Auby et al. [52] have I/VII/VIII 23 ±1 kbar 678+ 8 K established a weak transformation probably of

4 first order around 593 K with A T ~ 30 K. They also have a weak linear temperature dependence above found a second order transformation around 733 K. Tt . On the contrary, Unruh [70] and Oshima and

The II —> I transformation at 933 K was accom- Nakamura [71] have observed that the behaviour panied by a slight change in volume [52]. With of dielectric constant is governed by the Curie- increasing temperature the a parameter was found Weiss law above Tt ( Tc ). Couture-Mathieu et al. to undergo a much larger dilation (8.264^8.882 A) [62] and Freymann [61] find a normal behaviour at than the b (10.977-11.152 A) and the c (6.276- high frequencies (i.e., the dielectric behaviour o 6.433 A) parameters [53]. The electrical conduc- shows a radical change at some frequency between tivity of CS2SO4 was found to be enhanced above 10 kHz and 24 GHz); the lower limit of frequencies — 723 K [54] possibly due to the II > I transition. at which (NH 4 ) 2 S0 4 exhibits a normal type of dielectric behaviour occurs in MHz region [67]. The 3.2. Ammonium Sulfate rate of warming and cooling the crystal near Tt

The room temperature phase of (NH 4 ) 2 S0 4 has an markedly affects the shape of the low frequency e orthorhombic unit cell space group Pnam, Z — 4, versus temperature curve. Thus, with an extremely a— 7.73 A, b= 10.50 A, and c=5.95 A [55]. Ammoni- slow rate of temperature variation, normal dielec- um sulfate undergoes a polymorphic transformation tric behaviour is observed [72]. Bodi et al. [73] have around 223 K as shown by various techniques studied the behaviour of the complex dielectric [56—63]. Mathias and Remeika [64] discovered that constant of unirradiated and gamma-irradiated below 223 K (NH 4)2S0 4 is ferroelectric parallel to the ferroelectric ammonium sulfate in the microwave -2 region as a function of temperature. They find to a-axis, P s and E c at 215 K being 0.254 jiC cm and Tt 2.0 kV cm -1 respectively. Kamiyashi and Miyamoto shift from 238 K to 226 K for the irradiated sample. ,

[65], however, reported the transformation to occur Tt is also affected by the application of a dc electric in the temperature range 237—244 K for single field along the [110] direction of the crystal [74] and crystals and around 220 K for polycrystalline by the pressure under which the study is made [75]. material. Singh [66] has studies the crystal struc- Hoshino et al. [67], however, could not detect any tures of the room-temperature as well as the low- noticeable shift of Tt by any of the above effects.

. polarization temperature phases of (NH 4) 2 S0 4 The refinement These authors report spontaneous of the room-temperature structure indicates that below Tt not to depend on temperature. Ikeda et al. the actual crystal is a statistical mixture of two [76] show that the anomalous temperature depend- enantiomorphic states, the true symmetry being ence of the dielectric constant, spontaneous polar- Pna2i rather than Pnam. Neutron diffraction studies ization, spontaneous strain and elastic compliance of Singh [66] have shown that two ammonium ions can be explained in terms of the temperature which are crystallographically unrelated also have dependence of the order parameter. Unruh [77] has different surroundings. NH+(I) involves a hindered found the spontaneous polarization to strictly rotation at room temperature about the polar c-axis depend on temperature. The NH7 ions in the para-

and its rotation persists below the Tt . NH+(II) is electric phase oscillate with large amplitudes and disordered around the plane at Z — i above the this continues even in the ferroelectric phase. At

lower temperatures than Tt , NHf ions show dual Tt and is ordered below. In the low temperature + phase, (II) shows five H-bonds of normal behaviour [78]. Consequently, changes in the orien- NH4 strength which are responsible for the dielectric tation of dipoles are related to NH+ (I) and NH+ (II) polarization of ammonium sulfate. Numerous ex- ions and they can possibly affect the orientation of perimental results [67-69] lead to the conclusion SO^ 2 ion with change in temperature. This leads that the transformation in (NH^SQ* is of first order. to a temperature dependent P s [79]. The lattice

Results of dielectric measurements on (NH 4 ) 2 S0 4 parameters and birefringence of (NH 4 ) 2 S0 4 also by different workers are not entirely in agreement. show anomalous dependence on temperature [67,

Hoshino et al. [67] notice an unusual shape of the 80]. Anistratov and Martynov [81] show that the dielectric constant versus temperature curve. The anomalies in birefringence at the Tc (or Tt ) are due dielectric constant measured in the direction of the to the spontaneous deformation of the crystal.

ferroelectric c axis was found not to depend on Around Tt, electrical conductivity increases pos- temperature in the paraelectric phase. Koptsik et sibly because of the formation of cracks in the al. [68], however, show the dielectric constant to crystal near the transition [82].

5 H

Blinc and Levstek [83], from their studies of structural change in the crystal where the symmetry NMR and IR spectra have suggested that above plane perpendicular to the ferroelectric axis is lost 173 K the NH^ groups reorient about random axes in the low-temperature phase. In the high-tempera-

with a frequency higher than 10 5 Hz. There is no ture phase, while each of the NHJ ion has only one o o H — O bond of 2 A, there are bonds of 1.9 A in the change at T t , but a line-width transition occurs

below 163 K. Below 77, two components can be ferroelectric phase. resolved, which have been interpreted as being due From proton and deutron magnetic resonance to “frozen in” and rotating NH^ ions, respectively. measurements, O'Reilly and Tsang [92, 93], on the other hand, find a definite change in the dynamical In the IR spectrum of (NH 4 ) 2 S0 4 [84], the splitting -1 of the wide band at 3235 cm into a doublet (with behaviour of NH^ ions. They conclude that the -1 components at 3190 and 3290 cm ) below 223 K is phase transition in (NH 4 ) 2 S0 4 is of the order- probably due to the tunnelling of a proton along the disorder type and is caused by the ordering of -1 N — H . . . 0 bond. A very narrow band at 963 cm distorted tetrahedral NH^ ions which carry a dipole

also appears when (NH 4 ) 2 S0 4 transforms to the moment of 0.11 D relative to the crystallographic ferroelectric state. These results and the absence plane. Dahlborg et al. [94] commenting on the con-

of Curie point shift on dueteration [67] do not permit troversy of the findings of Hamilton [95] and the ferroelectric properties of the crystal to be at- O’Reilly and Tsang [92, 93] held that the methods ributed to hydrogen bonding. Schutte and Heyns [85] used were sensitive to different intervals of time. -1 find that the 2v 2 line at ~ 3300 cm disappears at The characteristic time of a neutron-diffraction

Tt . In this mode of vibration, the H-atoms move on measurement is considerably different compared to the surface of a sphere whose radius is the N — the frequency of the oscillating field (42 MHz) em-

bond distance. ployed by O’Reilly and Tsang [92]. Thus, the different results can be explained on the basis of Raman studies by Bazhulin et al. [86] show that the the different time scales; further, the measurements intensity of bands depend on the orientation of the were made at different temperatures. Dahlborg et al. cyrstals during excitation of the spectra by natural [94] find the transition to be of dynamic nature. The and polarized light. Some additional bands besides change in the dynamics of NH/ ions is related to the those corresponding to the internal vibration of structural change in the lattice. The transition is SO|“ ion are also seen. Stekhanov and Gabrichidze not sharp, but extends over some twenty degrees [87] report that the band maximum due to valence in the time scale seen by the neutron. Far below vibrations of NH|, is displaced toward the smaller

-1 Tc , the ions perform translational and torsional frequencies by 150 cm at the transformation of the 1() oscillations during a time longer than 10~ s. Above crystal through the Curie point. These authors are T due to thermal fluctuations in the system, the of the view that hydrogen bonds play an important c , ions are capable of performing rotational motions role in the appearance of the ferroelectric effect in 11 during a considerable length of time (> 5 X 10“ s). (NH 4 ) 2 S0 4 . Recently Jain et al. [88] from their IR The rotational motions of adjacent groups are studies reported that the ferroelectric phase transi- believed to be coupled. These authors support the tion in (NH 4 ) 2 S0 4 is primarily due to sudden dis- view of O’Reilly and Tsang [92, 93] that the transi- tortion in the SOj 2 ions. tion is of order disorder type. Inelastic neutron scattering investigations by Nuclear spin-lattice relaxation studies of Rush and Taylor [89] show the rotational freedom of (NH 4 ) 2 S0 4 reveal a definite change in the proton the ions to undergo only a very small change in relaxation behaviour in the neighbourhood of the passing through the transition. Bajorek et al. [90] Curie point (77) indicating a change in the state found a jump in the variation of the elastic intensity of motion at the transition. The results suggest that

at the Tt in their neutron scattering study. Schlem- the ferroelectric transition in (NH 4 ) 2 S0 4 is accom- per and Hamilton [91] have arrived at the same con- panied by a change in lattice structure which alters clusion from their neutron diffraction study. They the potential in which the nuclei move, but does not report that the transition is not of the order-disorder involve an important change in the degree to which type, but rather involves a change in the hydrogen nuclei must cooperate in order to surmount the 2 bonding of the ammonium groups to the S0 -prime potential barriers [96]. Jain and Bist [79] recently which in turn results in stronger hydrogen bonds in developed a point charge model to compute the the ferroelectric ~ 2 phase. This becomes possible by a spontaneous polarization (Ps ) 0.42 fiC cm which

6 agrees well with the experimental value reported form (soluble anhydrite, CaS0 4 (III)) which changes 2 by Hoshino et al. [6]. According to them [79] SOy rapidly to hemihydrate in the presence of water ions also contribute to the total spontaneous vapor; 3, anhydrous modification identical to anhy- polarization of (NH 4 ) 2 S0 4 . drite (CaS0 4 (II)), and 4, at ~ 1473 K, a stable high

The crystal structure as well as the physical temperature form (CaS04 (I)) which decomposes properties of (ND 4 ) 2 S0 4 are similar to (NH 4 ) 2 S0 4 afterwards. [67, 97, 98], CaS0 4 (III) is a metastable phase and under 3.3. Alkaline Earth Metal Sulfates equilibrium conditions, transformation takes place

directly to CaS0 4 (II). Florke [108] and Newmann Among the alkaline earth metal sulfates, BeS0 4 [115] have shown that CaS0 4 (I) cannot be quenched exhibits two polymorphic transformations while all at room temperature. A number of workers have the other sulfates undergo one transformation. The confirmed the presence of a high temperature size of the ions seems to be the major factor con- thermal anomaly in CaS04 [101, 116, 117, 118]. trolling these transformations [99]. The available Deer et al. [117] have pointed out that the high data on the phase transformations of alkaline earth temperature heat effect might be associated with metal sulfates are shown in the table 1. Table 2 the onset of rotation of SOy 2 ions and not with gives the crystal structure data of the various a transition to another distinct crystal structure. phases. Gutt and Smith [102] observed a sudden lower- Relevant data on some of the individual alkaline ing of birefringence on heating CaS0 around earth sulfates are presented below. 4 1473 K leading to an isotropic state. This inversion Magnesium sulfate heptahydrate. MgS0 4 • 7H 2 0 was fully reversible and reproducible provided the has an orthorhombic unit cell with the space group specimen was not heated to a temperature far ex- D2-P2 2 2 ,Z = and a= 11.86 A, 6 = 11.99 A and 1 1 1 4, — ceeding the 7V The II > I transformation is ac- c = 6.858 A at 298 K [111] Chihara and Seki [112] companied by a considerable volume increase. reported a phase transformation without dehydra- Gutt and Smith [102] have concluded that the high tion in MgS0 4 • 7H 2 0 at 362—368 K. The Tt is sensi- temperature microscopic observations of a sudden tive to external conditions and sample history. change in birefringence cannot be explained by the Employing radioactive isotopes, Purkayastha and rotation of SO y 2 ions. Sarkar [113] reported the dehydration transition — MgS0 4 • 7H 2 0 » MgS0 4 • 6H 2 0 to occur at 298 ± DTA investigations of gypsum have shown an

0.5 K. MgS0 4 • 6H 2 0 has a monoclinic unit cell with exothermic heat effect at ~ 623 K possibly due to o the space group A2/a, Z = 8, and a = 24.34 A, b — III II transformation [119, 120]; Berry and Kuntze = 98°34' 7.15 A, c= 10.04 A, /3 [114]. [121] have reported the Tt to be 665 K. This trans- Calcium sulfate. Naturally occurring calcium formation does not involve a simple monotropy, sulfate is found in two forms, gypsum (CaS0 4 '2H2 0) but represents the precipitation of anhydrous CaS0 4 and anhydrite (CaS0 4 ). By heating gypsum at with the loss of interstitial water from the phase III successively high temperatures, four modifications solid solution [122]. The decrease in volume o 3 can be prepared [115]: 1, CaSO 4 -0.5H 2 O (hemi- (—10 A ) per CaS0 4 formula group prohibits the hydrate); 2, an extremely hygroscopic anhydrous subsequent rehydration of the anhydrous compound.

Table 1. Phase transformation data

1 -1 -1 Sulfate Transformation Tt K A kcal mol A Str, cal mol References , K Htr ,

III -> II BeS0 4 863-883 [ 3.3 [8, 100] II -> I 908-913 \

MgS0 4 II I 1283 ± 10 [101]

CaS0 4 II ^ I 1453 5.0 3.4 [5] 1486 [102]

-» SrS0 4 II I 1425 ± 5 [5, 103]

-»> BaS0 4 II I 1422 [5]

7 Table 2. Crystal data of the stable phases

Sulfate Phase Crystal system Space group Z Cell dimensions References (temperature)

BeS0 4 III (room Tetragonal (body 14 2 a = 4.485 A [104] temperature) centered) c = 6.90 A

II (883 K) Orthorhombic 2 o = 6.58±0.01 A [8] (pseudo tetragonal) b = 4.606 ±0.005 A c = 4.675 ±0.005 A

I (923 K) Cubic (face centred) a = 6.65 ±0.03 A [8]

MgS0 4 II (below T,) Orthorhombic D^-Cmcm 4 0 = 5.182 A [105] 6 = 7.893 A c = 6.506 A

I (above Tt) Orthorhombic D.]®-Pbnm 4 0 = 4.742 A [106] 6 = 8.575 A c = 6.699 A

CaS0 4 II (299 K) Orthorhombic D^-Cmcm 4 0 = 6.238 A [107] 6 = 6.991 A c = 6.996 A

I = (above Tt ) Cubic (face centred) a 7.82 A* [108]

SrS0 4 II (299 K) Orthorhombic Dl^-Pnma 4 o = 8.359 A [109] 6 = 5.352 A c = 6.866 A

I (above Tt ) Cubic a = 7.11 A* [108]

BaS0 4 II (299 K) Orthorhombic Dl^-Pnma 4 0 = 8.878 A [110] 6 = 5.450 A c = 7.152 A

I (above Tt ) Cubic a = 7.21 A* [108]

*Changed from kx units where lkx = 1.00202 A.

Barium sulfate. Florke [108] has observed the by any change in enthalpy. Urazov and Bashilova

II —^ I transformation in the range 1343—1383 K. [128] in their thermographic investigations have

to in II —> I transition at 773-778 K. DTA Hahn emanation technique has revealed T t be observed the the range 1393-1453 K on heating and 1373-1343 K and high temperature x-ray diffraction studies of on cooling [123]. Majumdar and Roy [45] show a hexagonal modifica-

tion to be the stable polymorph above T t , at atmo- 3.4. Thallium Sulfate spheric pressure. They report an irregular volume

. the The room temperature phase of T1 2 S0 4(II), has expansion near Tt Majumdar and Roy [45] find an orthorhombic unit cell, with space group D|)>— behaviour of T1 2 S0 4 to be similar to that of K 2 S0 4 . Pmcn, Z = 4 and a = 5.923 A, 6=10.66 A, c = Dworkin and Bredig [49] disagree with Majumdar

7.828 A [124]. T1 2 S04(II) transforms to T12 S0 4(I) and Roy in this regard. While in K 2 S0 4 most of the at 765 ±4 K [125]. In their dilatometric studies, transformation occurs isothermally at ~ 857 K -1 Samen and Tammann [126] had observed in 1903 (A// tr ~2 kcal mol ), the corresponding trans- that T1 2 S0 4 goes through a sharp volume change in formation in T1 2 S04 has a very small isothermal part -1 the vicinity ' of 703 K. Fischmeister [127] has found ( A// tr 160 cal mol at 774 K) and is predomi- that the volume change at 703 K is not accompanied nantly a gradual pretransitional process. The differ-

8 ence might be attributed to the high polarizability nitrogen temperature. The monohydrate exhibits + of the Tl ion. strong exchange interaction as seen from the nar-

rowness of the paramagnetic resonance lines [147]. 3.5. Lead Sulfate The curve of electric resistance with pressure up to 59.5 kbar at 353 K shows a sharp change in slope DTA investigations of Gruver [29] reveal a single at 17.1 ± 1 kbar. This has been attributed to freezing endothermic peak at 1158 K, apparently represent- of a saturated aqueous solution of MnS0 4 [134]. ing an inversion temperature in PbS04 described Iron sulfate. FeS0 4 undergoes a transformation to earlier [129]. an antiferromagnetic state at 21 K [148] and Curie- Weiss law is valid in the range 45—90 K. Specific 3.6. 3 d Transition Metal Sulfates heat measurements on FeS0 4 • 7H 2 0 reveals a At ordinary conditions, the sulfates of divalent maximum at 2.3 K [149]. In the heptahydrate. Curie 3d transition metals do not show any clear thermal law is applicable between 64 and 290 K. Between 20 phase transformations except for those of cobalt and 14 K, however, the susceptibility increases and zinc. Most of these sulfates undergo magnetic much less rapidly than the high temperature transitions at very low temperatures. Some of the Curie constant would require. compounds especially MnS0 Cobalt sulfate. In addition to the two well known 4 , CoS0 and 4 , NiS04 ,

phases, a third phase CoS0 4 (III) was found to exist ZnS04 , exhibit high pressure transformations.

Table 1 and table 2 give the phase transformations along with the form CoS0 4 (I). CoS0 4 (III) is pos- and crystal data of the 3d-transition metal sulfates. sibly monoclinic (P2i/m) with dimensions a = 4.71 Trivalent 3d transition metal sulfates like A, 5 = 6.70 A, c = 4.75 A and £ = 66.2° [150]. et al. measured the magnetic Cr2 (S04 )3 do not undergo any phase transitions Borovik-Romanov [148] in the anhydrous state in the temperature range susceptibility of CoS0 4 in the temperature range

• typical of an 100-295 K [130], The hydrated sulfate Cr2 (S04 )3 13 K—300 K and observed a maximum

18H2 0, however, shows possibly a second order antiferromagnetic transition near 15.5 K. Curie- transition around 195 K. This transition has a Weiss law is obeyed at temperatures appreciably at marked effect on the dielectric properties due to higher than Tt , but lower temperatures, the the freeing of the polar molecular groups [131]. temperature dependence of the magnetic suscepti-

Ferric sulfate exists in two modifications [132], bility deviates widely from the Curie-Weiss law in one crystallizing in the rhombohedral space group the paramagnetic range and displays an anomalously R3, Z = 2, a = 8.791 ± 0.004 A, a = 55°52' and the large decrease in the antiferromagnetic range. This other in the monoclinic space group, P2i/n, Z = 4, is possibly due to the splitting of the ground state +2 with a = 8.296 ±0.002 A, 5 = 8.515 ±0.002 A, of the Co ion by the crystalline field. Kreines [151] c = 11.600 ±0.002 A. /3 = 90°30'. Thermodynamic measured the magnetic susceptibility in the tem- 1.3—300 In fields data for Fe 2 (S0 4 ) 3 indicate a minor transition perature range K. magnetic up -1 ~'4 at 800 K with AH tr of 540 cal mol [133]. to kOe, the susceptibility was independent Additional information regarding the phase of the field intensity. The x-value reached a maxi- transformation of these sulfates is given below: mum along the 3 crystal axes at 12 K. Below this

Manganese sulfate. MnS0 4 shows a magnetic temperature, x along each axis was different. The phase transition at 11.5 K which is the Neel tempera- magnetic moment reached its maximum value at ture (Tn ) [143]. Specific heat measurements [144] 4.2 K. Borovik-Romanov and Kreines [152] showed have confirmed thfs value of TN and in addition show that CoS04 undergoes a ferromagnetic-antiferro- three other peaks between 5 K and 11.5 K. Two of magnetic transformation around 12 K ( TN ). Brown these peaks correspond to the two phase transi- and Frazer [153] and Ballestracci et al. [154] re- tions theoretically predicted by Solyom [145]. ported the structure of the low and high tempera-

MnS0 4 H2 0. The Neel temperature for MnS0 4 * ture phases of CoS0 4 by neutron diffraction studies,

H 2 0 has been reported to be 16 K [143]. Date [146] confirming the earlier x-ray diffraction results. has reported some anomalies in the measurements Nickel sulfate. Borovik-Romanov et al. [148] of paramagnetic resonance and susceptibilities. found a maximum in magnetic susceptibility at This sulfate showed no resonance absorption in ~ 37 K characteristic of an antiferromagnetic the liquid helium temperature region but showed transition. Curie-Weiss law was found to be obeyed a strong paramagnetic resonance above liquid in the temperature range 45—300 K. In the 14—34

9 K

Table 1. Phase transformation data

Transition at atmospheric

Sulfate pressure Transition at high pressures Remarks References

MnSO.4 1^ II 55.2 ±3 kbar (771 K) [134] II- *111 73.5 ±3 kbar (771 K)

III -*IV 96.6 ±6 kbar (771 K)

FeS04 I^II 5 kbar (1073-1123 K) A polymorph [135] obtained by quenching

FeS0 4 at 1073-1123

Tt 705 ±8 II 6.1 ± 1 kbar (773 K) [5, 134] C0SO4 , K I- -1 1 AH tT , 1.6 ±0.1 kcal mol I- III 25 ± kbar (773 K) -1 AS tr , 2.3 ±0.2 cal mol K I'- IV 31 ±2 kbar (623 K) - ll ^ III 20.6 ± 1 kbar (973 K) III -^IV 37.7±2 kbar (773 K) IV ^v 40.6 ±2 kbar (773 K) V- * VI 48.8 ±2 kbar (773 K) VI VII 98 ±5 kbar (773 K)

NiSO, I- II 19 ± 1 kbar (773 K) [134] I- III 25 ±2 kbar (573 K)

II- III 29 ±1.5 kbar (773 K) III ->IV 41.8±2 kbar (773 K) IV —> V 65 ±3 kbar (773 K) V- -> VI 94±5kbar (773 K)

VI-—> VII 106.5 ±6 kbar (773 K)

VI -j—» VIII 108 ±7 kbar (943 K) VII- VIII 112.3 ±6 kbar (773 K) VIII IX 123±6kbar (773 K)

CuSCT I — II ~ 50 kbar At all [134] temperatures between 523 K and 775 K

ZnSO II -> I I —> II 22.8 ±2.5 kbar (773 K) [5, 29, 134] T,, 1013 K I—> III 10 kbar (1053 K)

I —> IV 15 kbar (1063 K) I->V 28.0 ±1.5 kbar (773 K) II-^VI 37.0 ±2 kbar (773 K)

III -> IV 16.0 ±2 kbar (1 123 K)

VI —> VII 50.1 ±3 kbar (773 K) VII -» VIII 73.2 ±3.5 kbar (773 K) VIII -> IX 86.7 ±4 kbar (773 K) IX ^X 96.8 ±5 kbar (773 K) X -» XI 102.6 ± 6 kbar (773 K)

10 Table 2. Crystal data for known phases

Sulfate Phase Crystal system Space group Z Cell dimensions References

room temperature MnS0 4 orthorhombic D Cmcm 4 a = 5.248 A [134] 6 = 8.048 A c = 6.842 A

MnS0 4 -H 2 0 room temperature monoclinic A2/a-C|h 4 0 = 7.758 A [136] 6 = 7.612 A c = 7.126 A f}= 115°42.5'

temperature FeS0 4 room orthorhombic D^-Cmcm 4 0 = 5.261 A [137] 6 = 8.013 A c = 6.454 A

FeS0 4 • 7H 2 0 room temperature monoclinic C|a -P2i/c 4 a=14.072 A 6 = 6.503 A c= 11.041 A °34' /3 = 105

CoS0 4 room temperature orthorhombic D^-Cmcm 4 a = 5.191 ±0.002 A [139, 140] 6 = 7.864 ±0.002 A c = 6.516± 0.002 A

high temperature orthorhombic D^-Pnma 4 o = 4. 738 ± 0.002 A 6 = 8.603 ±0.002 A c = 6.699± 0.002 A

NiS0 4 room temperature orthorhombic D^-Cmcm 4 o = 6.338± 0.002 A [114] 6 = 7.842 ±0.001 A c = 5.155 ±0.001 A

CuS0 4 room temperature orthorhombic D^-Pmnb 4 0 = 6.6982 ± 0.0006 A [141] (299 K) 6 = 8.3956 ± 0.0006 A c = 4.8291 ±0.0004 A

CuS0 4 • 5H 2 0 room temperature triclinic 2 0 = 6.113 A [114] 6=10.712 A c = 5.958 A a = 97°58' /3= 107°17' y = 77°26'

ZnS0 4 room temperature orthorhombic D^-Pnma 4 a = 8.588 A [142] (298 K) 6 = 6.740 A c = 4.770 A

K range, the susceptibility of NiS0 4 in the anti- remains disordered and causes an increase in the ferromagnetic state varies with temperature ac- susceptibility. Curie-Weiss law is valid in the tem- cording to a quadratic law. perature range 40-300 K. Kido and Watanabe [156] Copper sulfate. Anhydrous copper sulfate shows have found the Curie-Weiss law to be valid in the an abrupt break at 35 K in the molar susceptibility temperature range 90-600 K. versus temperature curve [148,155] possibly due CuSO 4 • 5H 2 0. Taylor and Klug [157] discovered to the formation of an antiferromagnetic array in three polymorphic transformations at 302, 308, and half of the Cu +2 ions. The other half of the ions 326.7 K, respectively. Expansion coefficient and

11 DTA measurements [158, 159] confirmed all these Zinc sulfate. DTA investigations of Gruver [29] transitions to be second order. High temperature on ZnS0 4 * 7H 2 0 (natural) show two endothermic DTA investigations between 548 and 998 K [160] effects at 473 K and 623 K, possibly due to the loss show no thermal anomaly. A number of workers of water of hydration. A reversible inversion is [161-164] have observed DTA peaks related to the reported for anhydrous ZnSCC at 1013 K. dehydration of pentahydrate. Kiriyama and Ibamoto 3.7. 4 d Transition Metal Sulfates [165] measured the temperature dependence of the dielectric constant and losses of CuS04 5H 2 O Silver sulfate exhibits a polymorphic transforma- 93—393 found dis- — in the temperature range K and tion (II >1) while CdS0 4 is reported to have two tinct dispersion of the dielectric constants at polymorphic transformations (III —> II —^ I). Data temperatures higher than 343 K. Geballe and on phase transformations as well as the crystal Giauque [166] showed that the magnetic system structures of known phases are given in tables orients under the restraining influence of direc- 1 and 2. tional crystal forces causing changes in internal energy. The heat capacity curve has a maximum at Table 1. Phase transformation data 1.35 K, a minor maximum at 0.75 K and possibly a third maximum at 0.25 K. Dehaas and Gorter Sulfate Transfor- Tt , K Atf tr ,kcal AS tr , cal Refer- [167] measured the magnetic susceptibility in the mation moR 1 mol -1 K -1 ences temperature range 14.3-290 K, and found Curie- Ag II -I 685 1.9 2.8 Weiss law to hold good. The measurements of 2S0 4 [5] magnetic anisotropy of CuS0 4 ‘5H 2 0 at different CdS0 4 III ^ II 773 [171] temperatures from 83 K to 299 K [168] revealed the crystal to be nearly magnetically uniaxial with II —> I 1073 [172] its two principal susceptibilities conforming roughly to the Curie law with different Curie constants. Magnetic measurements down to 1.6 K Additional information regarding these sulfates

[169] show this salt to approximately follow Weiss is given below. law with 0 = — 0.7° over the whole temperature Silver sulfate. Hedvall et al. [175] reported a range. Benzie and Cook [170] found that the suscep- higher Tt (703 ±3 K) from their DTA measure- tibilities measured in different directions with ments, the Tt being independent of the heating rate. respect to the crystallographic axes follow a Curie- On cooling, the high temperature form could be Weiss law. The discrepancy between these and supercooled up to 20° below Tt. Johansson’s previous results [168] were attributed to tempera- studies [176] indicate a heterogeneous process of ture independent paramagnetism. nucleation during this transition. Once started, the

Table 2. Crystal data for known phases

Sulfate Phase (temp) Crystal class Space group Z Cell dimensions References

4 II K) orthorhombic D/ -Fddd 8 a = 5.8167 Ag 2 S0 4 (298 h A [173] b= 12.704 A c= 10.269 A

CdS0 4 III (298 K) orthorhombic D^-Pmmn 2 0 = 4.7174 A [174] 6 = 6.5590 A c = 4.7012 A

CdS0 4 I orthorhombic a = 5.310 A [172] 6 = 8.157 A c = 7.180 A

12 transition proceeds very fast in a given crystal. 573-873 K, having a cubic structure. The second The transition could not be induced by contact modification at 903 K has a relatively complex with the low temperature form above 698 K. At the crystal structure. II->I transition, the electrical conductivity of Room temperature crystal data for the Eu, Gd,

Ag2 S 04 was found to increase rapidly by approxi- and Tb sulfate octahydrates are given in table 1. mately one decimal power [177]. Vesnin [178] reported an enantiotropic transformation around

Table 1 . Crystal data for some monoclinic rare earth metal 843 K. He found this transformation to be rather sulfates [186] slow. Cadmium sulfate. Maksimova [171] detected two Sulfate a b c P Z peaks in the DTA heating curves for CdS04 . ±0.003 ±001 ±0.004 ±1° Specimens prepared by different methods produce 102°14' different thermograms possibly due to difference in Eu 2 (S0 4 ) 3 8H 2 0 13.566 6.781 18.334 4 crystal structure. Maksimova found that CdS04 (III)

• 102°11' Gd 2 (S0 4 ) 3 8H 2 0 13.544 6.774 18.299 4 is non-homogeneous and consists of two types of aggregates with different refractive indices. Hetero- • 102°09' Tb 2 (S0 4 ) 3 8H 2 0 13.502 6.751 18.279 4 geneity was observed only in specimens whose thermograms show the double thermal effects. From the heating and cooling curves of CdS0 4 References Sholokovich and Zvorykina [179] showed a new transformation in the range 1119-1125 K. [1] Wells, A. F., “Structural Inorganic Chemistry”. Clarendon Press, Oxford (1962). 3.8. Rare Earth Metal Sulfates [2] Rao. K. J.. and Rao, C. N. R., J. Mater. Sci. 1, 238 (1966).

Forland. T., and Krogh-Moe. J.. Acta Chem. Scand. 11 Thermal anomalies in hydrated rare earth metal [3] , 565 (1957). sulfates have been reported by a number of workers [4] Polishchuk. A. F., Russian J. Phys. Chem. 47, 1088 (1973). which are mostly attributed to the loss [180-185] [5] Stern. K. H.. and W eise. E. L., “High Temperature Prop- of water of hydration. Zaitseva [186] from thermo- erties and Decomposition of Inorganic Salts". NSRDS— graphic, thermogravimetric, spectroscopic and NBS Publication 7, 1966

[6] Ingraham, T. R., and Marier. P., Can. Metal. Quart. 4, x-ray diffraction studies, showed EmfSChh • 8H2 0 169 (1965). to have one polymorphic transformation in the [7] Denielou. L.. Fournier, Y., Petitet. P. J.. and Tequi. C., not temperature range 678-738 K which could be C. R. Acad. Sci.. Ser. C, 2 70, 1854 (1970). related to the loss of water of hydration. Around [8] Bosik, I. I.. Novoselova, A. V., and Simanov, Yu. P., 573 K. the hydrated sulfate was found to change to Russ. J. Inorg. Chem. 6, 1295 (1961). Swanson, H. E., and Fuyat. R. K. “Standard X-ray Diffrac- an anhydrous cubic modification (a = 6.63 ± 0.01 A), [9] : tion Powder Patterns”, NBS Circular 539, Vol. II, p. 59 which on further heating changed to an equilibrium (1953). macrocrystalline state (678 K). TGA thermograms [10] Wyrouboff. G., Bull. Soc. Franc. Mineral. 14 , 316 (1890). did not show further weight loss in the 573-873 K [11] Kracek, F. C., and Gibson. R. E., J. Phys. Chem. 34, 188 range. There appeared another transformation in (1930). Kracek, F. C., and Ksanda. C. J., J. Phys. Chem. 34, the crystal structure (as found from x-ray studies) [12] 1741 (1930). above 873 K. which was not accompanied by any [13] Popov, M. M., and Galchenko, G. L., J. Gen. Chem. thermal effects. Thermograms for Gd2 (S04 )3 8H2 0 (U.S.S.R.) 21,2489(1951).

• and Tb2 (S04 )3 8H2 0, differ from that of Eu2 (S04 )3 [14] Moreau, R.. Bull. Soc. Roy. Sci. Liege 32, 252 (1963).

• F., 420 (1962). 8H 2 0 in not having the exothermic effect in the [15] Fischmeister. H. Monatsh Chem. 93, temperature range 678-738 K. At 473 K the crystal- [16] Rassonskaya, I. S., and Semendyaeva. N. K., Russ. J. Inorg. Chem. 15, 27 (1970). line hydrates apparently possess cubic structure [17] Hiittner. K.. and Tamman, G.. Z. anorg. Chem. 43, 225 with octahydrate up a = 6.36 ±0.02 A. Heating the (1905). to 573 K. leads to formation of compounds isostruc- [18] Tabrizi. D., Gaultier, M.. and Pannetier, G.. Bull. Soc. tural with anhydrous Eu-sulfate. For anhydrous Chim. France 935 (1968). A. G., Chem. Commun., Univ. Stockholm (3). 20 Gd-sulfate two more polymorphic modifications were [19] Nord, (1973). found at 823 and 923 K. respectively. Anhydrous K [20] Swanson. H. E.. Fuyat. R. K., and Lgrinic. G. M.. “Stand- Tb-sulfate shows two polymorphic modifications, ard X-ray Diffraction Powder Patterns”, N.B.S. (USA) the first, stable over the wide temperature range, Circular 539, Vol. Ill, p. 62 (1954).

13 [21] Swanson. H. E., Gilfrich. N. T., Cook, M. I., Stinchfield, [52] Auby, R. Bernard, M. J., and Massaux, M., C. R. Acad. R.. and Parks, P. C., “Standard X-ray Diffraction Powder Sci. Ser. C, 2 66, 425 (1968).

Patterns”, N.B.S. (USA) Circular 539, Vol. VIII, p. 48 [53] Tabrizi, D., and Pannetier, G., Bull. Soc. Chim. Fr. 4280 (1959). (1969).

[22] Pannetier. G., Tabrizi. D., and Gaultier. M.. Bull. Soc. Chim. [54] Ramasastry, C., and Acharyulu, B. S. V. S. R., Proc. Nucl. France, 1273 (1966). Phys. Solid State Phys. Symp., 15th, 3, 171 (1970).

[23] Swanson. H. E.. Gilfrich, N. T. , and Cook. M. I., “Standard [55] Wyckoff, R. W. G., “Crystal Structures”, Interscience

X-ray Diffraction Powder Patterns”, N.B.S. (USA) Publ. Inc. New York, Vol. 2, Ch. 8 (1951).

Circular 539, Vol. VII. p. 17 (1957). [56] Crenshaw, J. L., and Ritter, I., Z. Physik. Chem. B16,

[24] Lunden, A., Svantesson, E., and Sevensson, H., Natur- 143 (1932).

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4. The Phosphates

Substances Measuring Observations Remarks References technique

Lithium phosphate Crystallographic Tt , 775 K High temperature y-phase can be [1,2]

Orthorhombic, Pcmn studies Low Li 3P0 4 has the /3|| structure preserved metastably at ambi-

a = 6.07 A, 6 = 10.26 while high Li 3 P04 has the ent conditions by rapid cooling. = A, c 4.86 A (stable 7 H structure. The /3-phase is phase) stable at RT.

Sodium phosphate Crystallographic 473-573 is = Tt , K The y-phase cubic with a 7.56 [3,4] tetragonal and dielectric Low temperature form (a) trans- A at 873 K. a= 10.81 A measurements forms to high temperature

c = 6.84 A form (y). Between 110 and 180 (stable phase) K very rapid increase of e" occurs.

Ammonium phosphate NMR T„ 193 K These components belong to [5]

(NH 4 ) 3 po 4 The spectrum changes from a frozen in and rotating NH+ single line at RT to two com- ions. ponents at temperatures below

Tt .

16 4. The Phosphates — Continued

Substances Measuring Observations Remarks References technique

Dielectric At 262 K, an abrupt, almost dis- [4] constant and continuous increase is ob- loss served.

High pressure Details not available [ 6 ] studies up to 40 kbar

Crystallographic Calcium phosphate Tt , 1453 K High temperature form [7, 8] studies a-Ca3(P0 4 ) 2 , mono- /3-Ca3(P 0 4 )2 is hexagonal, clinic, P2i/a, = = 13.07 A, Luminescence Anomalies at 233 and 308 K R3c, Z = 8 with a = 10.345 A and 8 Z 8 , a [ ] 6 = 9.11 A, c= 12.86 and calori- appear in these c = 36.905 A. 108°9' A, /3 = metric measurements. (stable phase) measurements

Boron phosphate High pressure BPO 4 transforms from a cristo- High pressure form is quartz [9-1 1 J studies balite to a quartz form at 46 like hexagonal with a = 4.470 ± BP0 4 , hexagonal a = 4.332 A kbar 0.005, c = 9.926 ± 0.01 A and c = 6.640 A and Z = 3. (low cristobalite form, stable phase) Investigations up to 85 kbar at The dense modification has the temperature range 1273—1473 cell dimensions a = 7.75 ±0.02 K show a dense modification A, c = 9.95 ± 0.02 A and

of BPO 4 . Z = 9.

Aluminium Crystallography 7), 854 (rhombohedral to The transformation involves [1,10, 12] phosphate and TGA hexagonal) dilation in the c-direction as in

T, (rev) 847 K; AH lr , 2.64 quartz. AIPO 4 , hexagonal, -1 3 ,- 0.88 The crystal data for other forms P3i, Z = 3, a = 4.92 A cal g ; A Vi , + A c— 10.91 A (berlinite are as follows: form, stable phase) low cristobalite: orthorhombic, C222i

Z = 4, a = 7.099 ±0.003 A b = 7.099 ±0.003 A c = 7.006 ±0.003 A

tetragonal, 14, = 2 a = 4.99 A Z , c = 6.90 A Cristobalite, cubic,

Z = 4, a = 7.11±0.0lA at 623 K.

Crystallographic Three distinct modifications of The tridynite and cristobalite [13-15] were not found to convert and DTA studies AIPO 4 are obtained; tridymite, forms cristobalite and berlinite back to the berlinite on pro- (quartz structure). The 7]’s are longed heating. 363 K, 493 K, and 853 K, respectively.

EPR of The transformation is [16] +3 AlP0 4 :Fe confirmed.

has a complicated soft [17] Raman Confirmed the transformation. AIPO 4 spectroscopy mode lying at reciprocal lattice

points in A1P04 . These are Raman active. One such -1 mode is at 158 cm and is totally symmetric.

17 4. The Phosphates — Continued

Substances Measuring Observations Remarks References technique

High pressure Pressure-temperature curve for [10, 18.19] investigations the quartz-tridymite trans-

formation, determined up to 1 -1 kbar gave AHtr , ~ 262 cal mol . Polymorphic transformation near 55 kbar and 723 K. At 1173 K and 60 kbar two new' forms entirely different from the know n forms were obtained.

The 1273 K and 100 kbar, a third The third new form at 1273 K and form was found. 100 kbar has the crystal data: a = 5.11 A, 6 = 7.48 A, c = 6.09 A.

Crystallographic was found to exhibit three of 1 . 20 , 21 Gallium phosphate GaP0 4 The cristobalite form GaP0 4 , [ ]

GaP0 4 , hexagonal. studies and phases: can be easily converted to the

P3j, Z = 1, DTA 1. berlinite (low quartz) berlinite type by proper a = 4.902 A, 2. low cristobalite heat treatment. c— 11.05 A (stable 3. high cristobalite phase) Two phase transformations were detected corresponding to DTA peaks.

a. berlinite —> high cristobalite The low cristobalite form is ortho-

(a slow change) at 1243— rhombic C222i, Z = 4 1253 K.

b. low-cristobalite —» high a = 6.967 ±0.003 A cristobalite (a rapid and 6 = 6.967 ±0.003 A

reversible change) at 886- c = 6.866 ±0.003 A 896 K on heating and 843 —

Lead phosphate Crystallographic Low temperature monoclinic The high temperature form (I) [22. 23] cell. Pb 3(P0 4) 2 mono- studies. phase transforms to the high has orthorhombic unit clinic, -C2/c temperature around 473 K. D;^ -R3m C| h d Z = 4 Z=l, a = 5.53 ±0.02 A a— 13.816 A c = 20.30 ±0.05 A 6 = 5.692 A at 473 ±15 K. c = 9.429 A

and = 102.36° Heat capacity Measurements between 15 and [24] (stable phase) 300 K did not show any anomaly.

Bismuth phosphate Crystallographic Two phases monoclinic as well as The room temperature hexagonal [25. 26]

BiP0 4 , monoclinic studies hexagonal are the stable forms phase has the cell dimensions P2,/n-C! = 4 at room temperature. = h ,Z a 6.966 ±0.001 A a = 6.74 ±0.02 A c = 6.460 ±0.002 A 6 = 6.92 ±0.02 A

c = 6.46 ±0.02 A A third phase stable at high The high temperature phase

/3 = 103°30' temperatures was also dis- is monoclinic with the cell (monazite type, covered. dimensions stable phase) a = 4.88 ±0.03 A

The monazite type is the stable 6 = 7.06 ±0.02 A

form of BiP0 4 over a wide c = 4.71 ± 0.03 A

temperature range. /3 = 96.3±0.5° space group: 2 or P i~C 2 P2 ,/m

18 4. The Phosphates — Continued

Substances Measuring Observations Remarks References technique

The high temperature structure

slowly converts to the monazite

type at ordinary temperatures. No spontaneous change from the hexagonal to the monazite type has been detected.

Crystallographic, 1448 (/8->a) phase is an unstable phase [27, 28] Chromium phosphate Tt , K j8 = and hy- An amorphous form exists up to and converts to a-phase CrP0 4 (crystal DTA data not available) drothermal 1073 K. The reflections for gradually. studies the /1-phase appear at 1223 K.

Manganese phosphate DTA T<, 1086 ± 5 K Cristobalite type phase has the [29] (Quartz type phase converts cell dimensions: Mn (P0 4 )2, hexagonal 3 = a = 4.94 A to the cristobalite type) a = 4.97 A, c 6.97 A

c = 5.48 A

(stable phase) High pressures At the pressure ~ 55 kbar and [10] temperature 723 K, a new phase has been reported.

is found as [30-32] Iron phosphate Crystallographic Four varieties, orthorhombic, In nature FeP0 4 studies triclinic, monoclinic (dull red) strengite (orthorhombic) and and orthorhombic (pale green) phosphosiderite (monoclinic). forms were reported. The last Quartz type modification has three were, however, later the dimensions: found to be identical with no a = 5.035 A apparent points of trans- c = 5.588 X 2 A formation among themselves.

X-ray diffraction T 973-983 K (reversible Several inversions reported [29. 33] and DTA transformation) earlier were not confirmed.

High pressure Around 55 kbar and 723 K, [10]

studies FeP0 4 is reported to transform to a new form.

monoclinic [34. 35] to the (3-Zn (P0 4 ) 2 is also Zinc phosphate Crystallographic a-Zn 3 (P0 4 )2 transforms 3 with space group P2i/c, Z = 4, /3-Zn (P0 4 2 at 1215 K Zn 3 (P0 4 )2 studies 3 ) = 9.393 ± 0.003 A monoclinic a = 9. 170 ±0.006 A C« -C2/c, Z = 4 b ft = 8.686 ± 0.003 A a = 8.14±0.02 A c /!= 125.73°±0.10 6 = 5.63 ±0.01 A c= 15.04 ±0.04 A /3=105°08'±05'

(stable phase)

Crystal data (hexagonal) Z = 3, [36-39] Rare earth metal Crystallographic La, Ce, Pr, Nd, Sm, Eu, Gd, and space group phosphates studies Tb-phosphates have monazite type structure. Some of them P3i21(D|) a c also possess a hexagonal Phosphate 7.081 6.468 structure at RT. This hexagonal La- ±0.008 A ophase transforms to /1-phase ±0.005 A 6.439 on heating between 673 and Ce- 7.055 ±0.003 A ±0.005 A 1073 K. 7.00 6.39 Dy-, Ho-, Er-, Tin-, Yb-, and Nd-

19 4. The Phosphates — Continued

Substances Measuring Observations Remarks References technique

Lu-phosphates have zircon ±0.01 A ±0.03 A type structure (tetragonal, Gd- 6.89 6.32 space group Q®)- Tb-phosphate ±0.01 A ±0.02 A

also exists in zircon type Monoclinic monazite type, P2 i/n— = 4 structure. C 2 h , Z

Phosphate a b c La 6.83 7.05 6.48 103°34' Ce 6.76 7.00 6.44 103°38' Pr 6.75 6.94 6.40 103°21' Nd 6.71 6.92 6.36 103°28'

Crystallographic Phase transformations in SmP0 4 The x-ray diffraction pattern of [40]

studies and PrPO-t have been found at YbP04 after being heated at

873 K. Above 773 K, YbP04 1273 K is different from the undergoes a phase transition corresponding patterns of

like SmP04 and PrP04 . SmP0 4 and PrP04 . This high

temperature phase is tetragonal, space group I4i/amd (D^’) with a = 6.812 A, c = 5.973 A.

Magnetic The 7Vs in magnetically The Gd-, Tb-, and Dy-phosphates [41-43] measurements ordered rare-earth compounds, were found to have extremely which have no conduction high Neel temperatures of 225 electrons, are considerably low K, 415 K, and 505 K respec-

because of the weak ex- tively. Saji et al. [42], however, change interactions between differ from earlier results of

rare-earth ions. Wang et al. [41] suggesting antiferromagnetic transitions.

Erbium phosphate Magnetic From the temperature depend- A similarly low T, of 0.8 K has [44] measurements ence of the susceptibility in the been calculated from the esti- low temperature region where mated dipole interaction, indi-

only the lowest doublet is pop- cating that the exchange

ulated, a Curie temperature of interaction is very small or

— 1 K is extrapolated. This negligible compared to the di-

would place a transition to an pole interaction. ErP04 , there- antiferromagnetically ordered fore, may be a good example of

state below 1 K. a pure dipolar magnetic ordering.

Terbium phosphate Specific heat The plot of the specific heat With external fields more than 7 [45] and magnetic versus temperature shows two kOe the weak and strong direc- measurements A-type anomalies. One at the tions can be interchanged,

Neel point (Ts ), 2.20 ±0.05 K giving rise to a very sharp 7r/2 and the other at Curie point periodicity of the magnetization

(Tc ), 3.5 ±0.1 K, which has to perpendicular to the optical

be atrributed to a crystallo- axis, if the crystal is rotated

graphic phase transition from around the c-axis by 277. tetragonal to some lower symmetry. The magnetic measurements on single crystals show that there

is a strong magnetic anisotropy in the plane perpendicular to

the optical axis at temperatures

below Tc .

20 4. The Phosphates — Continued

Substances Measuring Observations Remarks References technique

Dysprosium phosphate Magnetic DyP0 4 is found to order anti- This appeared to be an ideal 3- [46-49] measurements ferromagnetically at approx. dimensional Ising antiferro- 3.5 K. magnet. The transition from the antiferro-

magnetic to the paramagnetic

state is first order, below a

critical temperature Tc near 0.75 K. This transition at higher

temperatures is of higher order.

Tt (paramagnetic-antiferromag- [50]

netic) in case of DyP0 4 has been reported to be 2.8 K.

Holmium phosphate Specific heat and At 1.39 K. a magnetic phase [51]

magnetic meas- transition is observed. urements

References [22] Keppler. 1., Z. Kristallogr. Kristallgeom. Kristallphys. Kristallchem. 132, 228 (1970).

[23] Keppler. U.. Ber. Deut. Keram. Ges. 46 , 244 (1969).

[1] “Crystal Structure Determinative Tables”, Ed. J.D.H. [24] Pitzer. K. S.. Smith. W. V.. and Latimer. W. M.. J. Amer. Donnay and G. Donnay, American Crystallographic Chem. Soc. 60, 1826 (1938).

Association (1963). [25] Deschulten, M. A., Bull. Soc. Chim. Paris 29 , 723 (1903).

[2] West, A. R.. and Glasser, F. P.. J. Solid State Chem. 4, [26] Mooney-Slater. R. C. I... Z. Kristallogr. 117, 371 (1962).

20 (1974). [27] Sullivan. B. M., and McMurdie. H. F.. J. Res. NBS (USA)

[3] Palazzi, M.. Remy, F., and Guerin. H., C.R. Acad. Sci. Ser. 48, 159 (1952).

C 272, 1127 (1971). [28] Shafer. M. W., and Roy, R., J. Amer. Chem. Soc. 78,

[4] LeMontagner. S. LeBot, J.. and Allain. Y., Compt. Rend. 1087 (1956).

235, 1199 (1952). [29] Shafer. E. C.. Shafer. M. W., and Roy, R.. Z. Kristallogr.

[5] I.evstek, I.. Proc. Intern. Meeting Molecular Spectroscopy, 108,263(1956).

4th. Bologna. 3, 123 (1959). published 1962. [30] Brasseur. P., Compt. Rend. 202, 761 (1936).

[6] Bridgman. P. W., Proc. Amer. Acad. Arts Sci. 76, 71 (1948). [31] Eschenko, L. S., Shchegrov, L. N., Pechkovskii, U. \ ., and

[7] Mackay, A. L.. Acta Crystallogr. 6, 743 (1953). Ustimovich. A. B., Russ. J. Inorg. Chem. 18, 478 (1973).

[8] Koelmans, K.. Engelsman, J. J.. and Admiraal. P. S., J. [32] Caglioti. V., Alti Accad. Lincei. 22, 146 (1935).

Phys. Chem. Solids 11, 172 (1959). [33] Dindune, A.. Konstants, Z., Ozolins, G., Kreile, R.,

[9] Schulze, G. E. R., Z. Physik. Chem. B24 , 215 (1934). Trushinska. V. A., and Vaivads. A., Latv. PSR Zinat.

[10] Dachille. F., and Roy, R.. Z. Kristallogr. Ill, 451 (1959). Akad. Vestis, Kim. Ser. (4), 499 (1971).

[11] Mackenzie, J. D., Roth, W. L., and Wentorf, R. H., Acta [34] Calvo, C., Can. J. Chem. 43, 436 (1965).

Crystallogr. 12, 79 (1959). [35] Stephens, J. S., and Calvo, C., Can. J. Chem. 45, 2303

[12] Troccaz, M., Berger, C., Richard, M., and Eyrand, L., Bull. (1967).

Soc. Chim. France, 4256 (1967). [36] Henschel, H., AEC Accession No. 42458, Rept. No. NP—

[13] Manly, Jr., R. I... Amer. Minerolg. 35, 108 (1950). 15162 (1963).

[14] Floerke. O. W., and Lachenmayr, H., Ber. Deut. Keram. [37] Mooney-Slater, R. C. L., Z. Kristallogr. 117, 371 (1962).

Ges. 39,55(1962). [38] Mooney, R. C. L., Acta Crystallogr. 3, 337 (1950).

[15] Beck. W. R.. J. Amer. Ceram. Soc. 32, 147 (1949). [39] Schwarz, H., Z. anorg. allegem. Chem. 323, 44 (1963).

[16] Lang, R., Datars, W. R., and Calvo, C., Phys. Letters A30, [40] Kuznetsov, V. G., Petushkova, S. M., and Tananaev, I. V.,

340 (1969). Russ. J. Inorg. Chem. 14, 1449 (1969).

[17] Scott, J. F.. and Katiyar. R. S., Indian J. Pure Appl. Phys. [41] Wang, F. F. Y., and Feigelson. R. S.. Proc. Conf. R.E. Res., 9, 950 (1971). 4th, Phoenix Ariz. 77 (1964) published 1965.

[18] Shafer. E. C., and Roy, R., Z. Physik. Chem. 11, 30(1957). [42] Wang, F. F. Y., Phys. Status Solidi 14, 193 (1966).

[19] Seifert, K. F., Fortschr. Mineral. 45, 214 (1967). [43] Saji, H., Yamadaya, T., and Asanuma, M., J. Phys. Soc.

[20] Perloff, A., J. Amer. Ceramic Soc. 39, 83 (1956). Japan 28, 913 (1970).

[21] Shafer, E. C., and Roy, R., J. Amer. Ceramic Soc. 39, 330 [44] Will, G., Lugscheidev, W., Zinn, W., and Patscheke, E., (1956). Phys. Status Solidi B46, 597 (1971).

21 [45] Schopper. H. C., Int. J. Magnet. 3, 23 (1972). [49] Koonce, C. S., Mangun, B. W., and Thornton, D. D., Phys.

[46] Wright, J. C., and Moos. H. W., Physics Letters 29A, 495 Rev. B4, 4054 (1971). (1969). [50] Will, G., Schafer, W., Scharenberg, W., and Goebel, H., [47] Rado, G. T., Phys. Rev. Letters 23, 644 (1969). Z. Ang. Phys. 32, 122 (1971). [48] Colwell, J. H., Mangum. B. W., Thornton, D. D., Wright,

J. C., and Moos, H. W., Phys. Rev. Letters 23, 1245 [51] Cooke, A. H., Swithenby, S. J., and Wells, M. R., J. Phys. C (1969). 6, 2209 (1973).

5. The Perchlorates

Substance Measurement Observations Remarks References technique

Lithium perchlorate Crystallog- No polymorphic transformation [1-4]

LiC10 4 raphy and DTA at normal pressures. Orthorhombic, Pmnb,

Z = 4 High pressure A high pressure phase transition [5]

a = 6.926 A studies is seen around 16.4 kbar b = 8.659 A c = 4.836 A (stable phase)

Sodium perchlorate Crystallography Tt , 577-586 K High temperature phase is cubic, [1-4, 6, 7] NaClCL and DTA (orthorhombic —* cubic) space group:

orthorhombic, The transformation is accom- F43m, Z = 4 Amma, Z = 4 panied by a volume increase a = 7.09 A at 587 K. 3 a = 7.06 ±0.02 A AVtr of 14.27 A per molecule.

b = 7.08 ±0.02 A There is not much hysteresis c = 6.48±0.02 A accompanying the trans- (stable phase) formation.

Dielectric A sharp increase in the dielec Small anomaly just before Tt [7,8]

constants constant at Tt , is observed. is possibly due to the prerota- e/7curve has a small maxima tion caused by the loosening of

slightly before the T,. the lattice structure.

The sharp increase in e at Tt must be corresponding to the onset of free rotation of CIO^ during the disordering of the lattice to the cubic structure.

Electrical Thermal at is anomaly Tt In NaClCL, the large difference [7] conductivity observed. in the ionic radii and a very high value of the e in the cubic phase suggests a Frenkel type disorder.

Thermoelectric A break in the a versus T is [7] power noticed at the 7). An abrupt

increase in a is found.

IR spectroscopy 7L581 K The transformation is reversible. [4. 8, 9] and micro A band around 935 -1 the cm , projection symmetric stretching frequency

measurements of CI0 4', disappears at the T,.

22 >

5. The Perchlorates — Continued

Substance Measurement Observations Remarks References technique

High pressure NaC104 has two high pressure NaC10 4 phase III, the phase [5, 10] studies transitions up to 50 kbar. stable at >30 kbar probably

has a structure similar to BaS0 4 .

Potassium perchlorate Crystallographic, T, ,573-579 (orthorhombic— The cubic phase has the crystal [1-3, 6, orthorombic, Pbnm, DTA and dilato- cubic) with AT, 5.6 K. data as follows: 11-13] -1 II 4^ N metric studies AH tr . 3.29 kcal mol space group: F43m II a = 7.2401 ±0.0023 A The transformation is accom- N b = 8.8373 ± 0.0030 A panied by a large volume a = 7.52 A at 583 K c = 5.6521 ±0.0040 A change. (stable phase)

Dielectric meas- An increase in e is observed at Rotation of C10“ is indicated [7.8]

urements the T,. by the results. Transformation

is an order-disorder type.

Electrical con- An increase in conductivity is The activation energy for the [7]

ductivity reported at the T,. cubic phase is less than that in orthorhombic phase.

Thermoelectric A break in the curve a vs T is KC10 4 indicates an increase in [7] power noticed at T,. a followed by a sharp decrease.

IR spectroscopy A band around 935 cm ', ob- The transition is reversible. [4, 8. 9] and micro- served in orthorhombic form.

projection disappears at T,.

High pressure Orthorhombic —> cubic transition No high pressure phase exists in [5. 14]

studies. line rises from 569 K at atmos- KC10 4 . peric pressure to 839 K at

11.3 kbar, where it is found to decompose explosively.

Rubidium perchlorate Crystallographic T,, 551-554 K High temperature phase is cubic [1. 2. 6] RbClO-t. ortho- and DTA wdth space group F43m, rhombic, Pbnm, studies. Z = 4 and a = 7.72 ±0.01 A Z = 4 at 573 K. a = 7.53 A

6 = 9.27 A Dielectric con- A sharp increase is observed at The transformation is an order- [8] c = 5.81 A stant the T,. disorder type. (stable phase)

Electrical con- An increase in conductivity is Energy of activation for conduc- [7]

ductivity observed at the T,. tion is less in cubic phase as compared to that of orthorhombic phase.

Thermoelectric RbC10 4 shows an increase in a [7] power followed by a sharp decrease after the transformation.

IR spectro- T,, 552 K Transformation is found to be [4. 8] -1 scopy and A band around 935 cm dis- reversible.

micro projec- appears at the T,. tion technique

23 5. The Perchlorates — Continued

Substance Measurement Observations Remarks References technique

High pressure RbCICH has a high pressure [5, 15] studies. transformation near 15 kbar with a volume change of

3 -1 less than 1.3 cm mol .

Cesium perchlorate Crystallographic, T 492-497 K The high temperature cubic [1, 2, 6, 11, 13] CsClCb, orthorhombic, DTA and dilato- (orthorhombic—> cubic) phase has the space group

Pnma. Z — 4 metric meas- The transformation is accom- F43m, Z = 4 and a — 8.00 ± 0.02 a- 7.79 A urements panied by a large volume A at 503 K. 6 = 9.82 A change. c = 6.00 A

(stable phase) Dielectric CsClOj shows a sharp increase Order-disorder type transition is [8]

constant of e at T,. suggested.

Electrical An increase in conductivity of The energy of activation in the [7]

conductivity CsCICh is noticed at the T,. cubic phase is less than that

in the orthorhombic phase.

Thermoelectric CsClO .4 shows an anomalous be- a increases with increase in [7] power haviour as a changes sign from temperature in cubic

negative to positive value. CSCIO4 .

High pressure CsC104 is found to have two Triple points [5, 16] studies (DTA, transitions with a volume IV/III/II 4.5 kbar 587 K -1 crystallography change of 3.5 cm3 mol in the I/IV/II 7.0 kbar 684 K and volumetric former. technique) The high pressure transition

III —> IV occurs near 1 kbar.

The transitions from II and IV

phases to I take place at 6.4 kbar, 692 K, and 17.1 kbar, 813 K, respectively.

Ammonium perchlorate Crystallography Tt , 513 K The cubic phase has the crystal [1, 17-21]

NH4 CIO4 , ortho- (orthorhombic-cubic) data: space group F43m,

hombic, Pbnm, Z — 4, NH4 CIO4 seems to undergo a Z = 4, a = 7.69 ±0.02 A at 516 a = 7.449 ±0.005 A phase transformation near 83 K.

6 = 9.202 ±0.006 A K also. The transformation is presum- c = 5.816±0.004 A ably occasioned by the onset (stable phase) of free rotation of CKTr ion. In addition f ion has also NH4 been reported to undergo free rotation.

DTA T,, 513 K DTA thermograms change with [22] AT, 15 K the thermal history of the

sample, and even with aging at ambient temperature.

Heat capacity The measurement do not support NH+ ion has been found to [23, 24] measurements earlier results showing a freely rotate. phase transformation at 83 K.

+ Crystallography, No phase transformation in 120 The free rotation of NH ion is [25, 26] 4 IR, Raman K-300 K range. Anomalies are also reported. spectra seen in the temperature ranges, 20-50 K and 100-110 K.

24 5. The Perchlorates — Continued

Substance Measurement Observations Remarks References technique

NMR The results are interpreted in The relaxation times are consist- [27] terms of reorientation of the ent with a barrier hindering re- - NH ion about random or orientation of 2.0 ±0.6 kcal. nearly random axes.

Cold neutron This also supports the principle [28] studies of essentially unrestricted rotational motion of the NH+ ion in the crystal lattice.

Optical micro- T,. 513 K [4] projection technique

High pressure NH 4 CIO4 is found to have a trans- The anomalous curvature of [5. 29]

studies formation accompanied by a Bridgman’s NH4 CIO4 11/111 3 volume change of < 1.3 cm transition line near 373 K is -1 mol . The usual ortho- due to a triple point involving

rhombic—> cubic transition was the phase found at atmos- followed to 4 kbar and 573 K. pheric pressure below 83 K.

NH4 CIO4 explodes violently in The explosion in NH4 CIO4 may the range 603-623 K at 2-3.6 be due to large volume change kbar although at atm. pressure upon transition which causes

it explodes only at 713 K. local pressure increase at the sample. No other transitions could be detected down to 123 K at atmospheric pressures.

Thallium perchlorate Crystallographic Tt . 539 K High temperature phase is [1]

TICIQj. ortho- studies (orthorhombic—» cubic) cubic, space group: F43m, rhombic, Pbnm, Z = 4 and a = 7.63 A Z = 4

a = 7.50 A Optical micro- Tt, 539 K The Thallium salt is particularly [4] 6 = 9.42 A projection more suited for microprojec- c = 5.88 A technique tion demonstration as the

(stable phase) orthorhombic form is strongly birefringent.

High pressure A high pressure phase III is Earlier, Bridgman reported the [5, 30]

studies found with the initial volume transition to accompany AFtr , 3 -1 3 -1 change AFtr , 5 cm mol < 1.3 cm mol . The triple point I/III/II is at 0.7 kbar and 553 K.

Silver perchlorate Crystallographic T,, 428 K The high temp, cubic phase has [1] AgCICh, ortho- (orthorhombic-cubic) the space group F43m. Z = 4 rhombic and a = 7.01 ± 0.01 A at 433 K.

Optical micro- T,, 428-432 K The silver salt begins decompos- [4, 31] projection Another transition appears to ing near T, studies take place at 375-383 K.

25 References [15] Pistorius, C. W. F. T., and Clark, J. B., High Temperatures- High Pressures 1, 561 (1969).

[16] Richter, P. W., and Pistorius, C. W. F. T., J. Solid State [1] “Crystal Data Determinative Tables”, Ed. J. D. H. Donnay Chem. 3, 197 (1971). and G. Donnay, American Crystallographic Association [17] Stammler, M., Orcutt, D., and Colodny, P. C., Advances in (1963). X-ray Analysis 6, 202 (1962). Gordon. S., and Campbell, C., Anal. Chem. 27, 1102 (1955). [2] [18] Mauras, H., C. R. Acad. Sci., Ser. C 272, 973 (1971). Khorunzii, B. I., and Il'in, K. G., Izv. Vyssh. Uheb. Zaved, [3] [19] Stammler, M., Brunner, R., Schmidt, W., and Orcutt, D., Khim Tekhnol. 15, 174 (1972). Advances in X-ray Analysis 9, 170 (1966). D., and Kaascht. E., Ber. 56B, 1157 (1923). [4] Vorlander, [20] Smith, H. G., and Levy, H. A., Acta Crystallogr., 15, 1201 Arts Sci. 76,9(1945). [5] Bridgman. P. W., Proc. Amer. Acad. (1962).

[6] Syal, S. K., and Yoganarasimhan, S. R., Inorg. Nucl. Chem. [21] Venkatesan, K., Proc. Indian Acad. Sci. 46A, 134(1957). Letters 9, 1193 (1973). [22] Simchen, A. E., Isr. J. Chem. 9, 509 (1971).

[7] Syal. S. K., Ph.D. Thesis, Indian Institute of Technology, [23] Westrum. Jr., E. F., and Justice, B. H., J. Chem. Phys. 50, New Delhi, 1973. 5083 (1969).

[24] Stephenson, C. C., Orehotsky, R. S., and Smith. D., in [8] Syal. S. K., and Yoganarasimhan. J. Solid State Chem. 10, 332 (1974). “Thermodynamic Symp. Heidelberg (Germany)”, Ed. K. Schafer, AZ-Werbung Weber Druck, Heidelberg (1967). [9] Galanov. E. K., and Brodskii, I. A., Sov. Phys. (Solid State) [25] Van Rensburg, D. J. J., and Schutte, C. J. H., J. Molecular 10, 2678 (1968). Structure 11, 229 (1972). [10] Pistorius, C. W. F. T., and Clark, J. B., High Temperatures- [26] Waddington, T. C., J. Chem. Soc. 4340 (1958). High Pressures 1,41 (1969). [27] Ibres, J. A. J., Chem. Phys. 32 , 1448 (1960). [11] Connell. Jr. L. F.. and Gammel, J. H., Acta Crystallogr. 3, [28] Rush, J. J., Taylor, T. I., and Havens, Jr., W. W., Bull. Amer. 75 (1950). Phys. Soc. 6,261 (1961). Markowitz, M. M., J. Phys. Chem. 505 (1957). [12] 61, [29] Richter, P. W., and Pistorius, C. W. F. T., J. Solid State

[13] Cabahe. J., and Benard, J., Bull. Soc. Chim. France 36 Chem. 3, 434 (1971).

(1961). [30] Clark, J. B., and Pistorius, C. W. F. T., J. Solid State Chem.

[14] Pistorius, C. W. F. T., J. Physics Chem. Solids 31, 385 7, 353 (1973).

(1970). [31] Vorlander, D., and Haberland, U., Ber. 55B, 2652 (1925).

6. The Chromates

Substance Measurement Observations Remarks References technique

Sodium chromate Crystallo- T,, 686 K [U] — Na2Cr0 4 , graphic and (orthorhombic > hexagonal)

orthorhombic, thermal meas- II—> I Amam, Z = 4 urements a = 7.138 A

b — 9.259 A High pressure Three new phases III, IV, and The triple points are given as [3] c = 5.861 A studies V appear at pressures up to follows: (stable phase) 45 kbar Pressure, Temperature, kbar K I/II/IV 11.3 ±1 745 ±5 II/III/IV 14.6 ±1 694 ±7 I/IV/V 20.4 ±1 809 ±7

Potassium Crystallo- T,, 952 K The transformation is accom- [1,4] chromate graphic and panied by change in color from

K 2 Cr0 4 , thermal yellow to red. orthorhombic measurements space group, Pnam

Z = 4 Thermal 7Y 939 K (a-^(3) Color change is attributed to [1, 5-7] — — a 7.61 A analysis some gradual change in /3

b— 10.40 A K 2 Cr0 4 and not due to poly- = — c 5.92 A morphic transformation, fi

(stable phase) K 2 Cr0 4 is hexagonal with a = 6.125 A c = 8.245 A at 978 K.

26 Q

6. The Chromates — Continued

Substance Measurement Observations Remarks References technique

Specific heat No transformation [8] between 80 and 300 K

Magnetic sus- X is independent of temperature. [9] ceptibility (89-723 K)

Dielectric From the behaviour of e' and e", The effect of different variables on [10] permitivity the development of the trans- the polymorphic transformation and loss formation process in time can can also be determined. be followed and transition rate can be determined.

High pressure No indication of polymorphism [11. 12] studies in the temperature range 293— 473 K up to 12 kbar, but there appear three new high pres-

sure polymorphs of K 2 Cr0 4 between 20 and 100 kbar. A triple point between the

phases a, y, and 8 is near 923 K at 28.5 kbar.

Strontium chromate Crystallographic A possible orthorhombic high [13] SrCrO-i, monoclinic study temperature phase at 1148 K. has been reported. P2 /n— h z=\ a = 7.081 A 6 = 7.388 A c = 6.771 A 5' /3 = 103°25' ± (stable phase)

-1 (I) Thallium chromate Crystallographic, Tt , 638 K. A//tr , 15 cal mol The second order phase transfor- [14-17]

Tl2Cr0 4 , Ortho- DTA and elec, Th 795 K (774 K on cooling) (II) mation around 638 K was dis- -1 rhombic, Pmcn conductivity AHtr , 70 cal mol puted by Sladky [12], a = 5.910 A studies The trend in variation of lattice The high temperature hexagonal 6=10.727 A constants also shows an phase has cell dimensions:

c= 7.910 A anomaly in Tl 2 Cr0 4 between a = 10.04 ±0.04 A (stable phase) 523 and 623 K. c= 16.28±0.08 A at 803 K.

Lead chromate Crystallography Tf . 980 K-1056 K PbCr0 4 , however, has also been [13, 18-20]

PbCr0 4 , monoclinic and thermal found to evolve oxygen around space group: analysis 873 K due to decomposition to

P2 = 4 and Cr . 1 /n-Cf h, Z Pb 2 Cr0 5 2 03 a = 7. 118 ±0.004 A 6 = 7.434 ± 0.004 A c= 6.794 ±0.004 A 0=1O2°25.5'±2' (stable phase)

27 6. The Chromates — Continued

Substance Measurement Observations Remarks References technique

Silver chromate DTA and Tt , 762-766 K At lower temperatures Ag 2 Cr0 4 [21-23] — Ag 2 Cr0 4 , ortho- electrical orthorhombic » hexagonal is an rc-type semiconductor,

rhombic, space conductivity (II) (I) which transforms to a p-type group: Pnma semiconductor at higher Z = 4 temperatures. a =10.063 ±0.011 A

b = 7.029 ± 0.004 A High pressure The II —> I transition tempera- [24] c = 5.540 ±0.002 A studies tures to 40 kbar were fitted as (stable phase) t(°C) = 479 + 2.3 P- 0.020 P2

References [14] Carter, R. L., and Margulis, T. N., J. Solid State Chem. 5, 75 (1972).

[15] Natarajan, M., and Secco, E. A., Can. J. Chem. 52, 712 [1] “Crystal Data Determinative Tables”, Ed. J. D. H. Donnay and G. Donnay, American Crystallographic Association (1974). (1963). [16] Bashilova, N. I., Russ. J. Inorganic Chem. 9, 57 (1964).

[2] Hartford, W. H., Ind. Eng. Chem. 41, 1993 (1949). [17] Sladky, J., Czech. J. Phys. B19, 123 (1969). Pistorius, [3] C. W. F. T., J. Chem. Phys. 43 , 2895 (1965). [18] Jaeger, F. M., and Germs, H. C., Z. anorg. Chem. 119, 145

[4] Shemtshushny, S. F., J. Russ. Phys. Chem. Soc. 7, 1052 (1921).

(1906). [19] Germs, H. C., Chem. Weekblad. 14, 1156 (1917). [5] Groschuff, E., Z. anorg. Chem. 58, 102 (1908). [20] Parkes, G. D., Mellor’s Comprehensive Treatise on In- Hare, A., Phil. Mag. 48, 412 (1924). [6] organic and Theoretical Chemistry, Revised Edition, Vol. [7] Amadori, M., Atti accad. Lincei, 22, 453 (1913). 11, Longmans Green & Co., London (1952). [8] Popov. M. M., and Kolesov, V. P., Zhur. Obshchei Khim. [21] Hackert, M. L., and Jacobson, R. A., J. Solid State Chem. 26,2385 (1956). 3,364(1971). [9] Baudet, J., J. Chim. Phys. 58, 845 (1961). Pistorius, C. W. F. T., and Krueger, E., Z. Anorg. Allgem. [10] Verzhbitskii, F. R., and Donskikh, T. M., Uch. Zap., Perm. [22] J. (1967). Gos. Univ. (159), 78 (1966). Chem. 3 5 2,222

[11] Bridgman, P. W., Proc. Amer. Acad. Arts Sci. 52,91 (1916). [23] Sladky, J., and Kosek, F., Collection Czech. Chem. Com-

[12] Pistorius, C. W. F. T., Z. Physik. Chem. 35, 109 (1962). munication 31,3817 (1966).

[13] Pistorius, C. W. F. T., and Pistorius, M. C., Z. Kristallogr. [24] Pistorius, C. W. F. T., and Boeyens, J. C. A., Z. Anorg. 117,259 (1962). Allgem. Chem. 372, 263 (1970).

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