American Mineralogist, Volume 65, pages 154-156' 1980

Crystal structure refinementof a cobaltian

J. LyNN Pnerr AND PETER BAYLISS Departmentof Geology,University of Calgary Alberta T2N lN4, Canada

Abstract

A crystal structurerefinement of a cobaltian ulknannite (Ni,Co)SbS,which has a pyrite- type structure with ordering of Sb and S, has been refned to a R value of 0.023 in space group P2,3. No conclusiveevidence for deviationsfrom cubic symmetry was found.

Introduction tion this unit-cell value lies within the experimental valuesof Bayliss(1969) for Nio,Coo'SbSof 5.926A The of ulhnannite (NiSbS) was and NL.Coo,SbSof 5.91lA. initially proposed by Ramsdell (1925); in this struc- A singlecrystal 120 x'70 x 60 pm was selectedbe- ture Sb is substitutedin one set of four sitesoccupied cause of its well-developedcube form This by S in the NiS, pyrite-type crystal structure.This re- {100}. was aligned on a precessioncamera u5ing Mo ducesthe cubic symmetry from Pa3 to the non-cen- crystal radiation along an a* axis. Photographs hlc0 and hOl tic P2r3, which allows the atoms to move along the showed no systematicabsences or deviation from a three-fold axes.This crystal structurewas confirmed cubic unit cell. by Peacockand Henry (1948)and Bokij and Tseno- The crystal was accurately centered on a four- kev (1954),and later refined by Takduchi (1957).Re- circle diffractometer with reflections 800' 800 and 080 cently Bayliss (1977a) refined an arsenian ullman- so that a* axis coincided with the diffractometer 4 nite, Ni(Sb,As)S, which is optically anisotropic and Integratedintensities of all reflectionsfrom one where an ordered substitution of Sb by As reduced axis. hemisphere were collected with MoKc radiation and the symmetryto Pl. Thereforewe decidedto check if a graphite 002 monochromator.Within the range 5o the substitution of Ni by Co would causea loss of <20<60",1235 reflectionswere scannedin duplicate symmetry in ulLnannite like that reported by Bayliss with the os;20scanmode at l" 20 per minute over the and Stephenson(1968) for a cobaltian .A scan width of 1.7" + tan d. Normally, l0-second cobaltian ullmannite (D27860) from Broken Hill, countswere measuredat both the begin- New South Wales,was obtained from the Australian background ning and end of each reflection,except where the to- Museum for this study. tal counts were less than 500; background counts were then measuredfor 60 secondsto obtain better Experimentaland results data. A standard reflection 020 was measuredevery The samplewas analyzedby electron microprobe 50 reflections throughout the data collection in order as previously describedby Stout and Bayliss (1975). to check experimentalstabilitY. The analytical results and derived chemical formula Background,Lorentz, polarization,and absorption basedupon a 4AXY model are presentedin Table 1. corrections were made by the method of Wuensch This compositionis closeto the end-membercompo- and Prewitt (1965).The linear absorption coefficient sition of ullmannite, exceptfor the substitutionof Ni of this cobaltian ullmannite is 231.3cm-', which re- by Co. The samplewas optically isotropic. sults in transmissionfactors between 0.21 and 0.33 A 114.6 mm Debye-Scherrerphotograph was for this crystal. The extinction factor described by taken with -filtered Cu radiation. A unit cell Zachariasen(196'7) and extended by Coppens and with a : 5.9218,4'was calculatedby the Nelson and Hamilton (1970)was calculated. Riley (1945)extrapolation method to 0 :90o. All re- From one hemisphere,l3l symmetry-independent flectionscan be indexedin spacegroup P2,3.In addi- reflections with 129 reflections above the lo level

0003-004x/80/0I 02-0 I 54$02.00 154 PRAT:7: AND BAYLISS: COBALTIAN ULLMANNITE 155

Table l. Electron microprobe analysisand atomic proportions Table 3. Observed stnrcture factors

Atom Weight% Weight% Atom.ic nKL .t hkL Fo hkL Fa NiSbS D27860 proportions 100 s.0(1) ?nn ??16) Rno Ni 27.6 23.3 010 4.2(1) o3o 4.1(3) oso Co !'flr r.oo 001 1.7(l) 003 9.7(5) 005

Sb ERO {' 1.00 1.00 0.021 sotropic pyrite (Bayliss, 1977b).The data were then 0.4 0.01| 1.00 s 16 1 14. A n 07 r refined in spacegroup Pl, but showedno di-fference 100.0 101.2 from previous refinements.Table 4 gives the inter- atomic distancesand anglesfor the cubic (P2,3) re- finement. Thesevalues are slmilar to thoseof arsen- were measuredin spacegroup P2,3, which has sys- ian ullmannite reportedin Table 4 of Bayliss(1977a). tematic absencesof &00with ft odd, 0k0 with k odd, and 00/ with / odd. All reflectionswere included in Discussion the refinement of the crystal structure by the least- All the atoms in the cubic crystal structure (P2,3) squares program (RFrNE4) of Finger and Prince of ullmannite occupy specialpositions on one of the (1975).All observationswere weighted accordingto three-fold axes in a group of four; therefore any w : l/do where o. is the standard deviation basedon small movement of any atom from a three-fold axis counting statistics.Initial positional parameters were or an ordering process within any group of four taken from Tak6uchi (1957). The neutral atomic atoms will causemost of the symmetryto disappear. scattering factors and anomalous dispersion correc- Therefore the refinement indicates that the tions were taken from the International Tablesfor X- atoms have randomly substituted for the nickel ray Crystallography(1974). The data were first re- atoms in this crystal structure. fined in spacegroup Y2r3to an R value of 0.023.The Although the weak odd-orderreflections (ft00, 0ft0, positional parameters,isotropic temperature factors, and 00/) are present,they may be causedby the mis- and extinction parameter are listed in Table 2. These use or malfunction of the electronics (Szymafski, valuesare similar to those of arsenian ullmannite re- 1979).However, since only 35kV was used,the elec- ported in Table 2 of Bayliss(1977a\. The final R val- tronics effect as describedshould not be observed. ues of the isotropic and anistropic model are the Theseweak odd-orderreflections were measuredat a same. position to avoid the Renninger effect. The crystal This R value indicatesthat the crystal structure is structurerefinement of the Pl model is similar to the basicallycorrect, but spacegroup P2,3 has systematic P2,3 model and the is optically isotropic. absencesof ft00 with ft odd, 0k0 with k odd, and 00/ Therefore if theseweak odd-order reflectionsdo in- with / odd; however,these reflections were observed dicate a movement of atoms from their position on (Table 3). The only spacegroup which allows all re- the three-fold axis, then this movement is below the flectionsto be observedwith this crystal structure is detection limit of this crystal structure refinement Pl similar gersdorffite to (Bayliss and Stephenson, and the optical measurement. 1968),arsenian ullmannite (Bayliss, 1977a), and ani- The substitution of Co for Ni in this cobaltian ull- mannite, (Ni,Co)SbS, does not distort the crystal Table 2. Positionalparam€ters, isotropic temperaturefactors, and extinction parameter structure as doesthe substitutionof Co for Ni in the cobaltian gersdorffite(Ni,Co)AsS, describedby Bay- Atom Site B(A,) 0ccupan cy Table 4. Interatomic distances and ansles Ni N.i 0.86 -0.0178(1) u.30 [a J Co 0.14 Atom Distance(A) Angle(') q c n 07 0.3816(2) 0.83(3) Ni-S ) ?7R S -Ni-s 99.5 As 0.01 Ni - Sb s - Ni - sb 83.4 sb 0.02 S-Sb 2 q1l - Ni - sb 90.5 Ni -s -Ni 116.7 sb sb r.00 0.6264(L) 0.55(1) Ni - sb - Ni 116.6 Ni -s -sb 100.5 Extinction paraneter-0.000018( 1) Ni '-sb-s 100.7 156 PRATT AND BAYLISS: COBALTIAN ULLMANNITE liss and Stephenson (1968). The probable ex- Akad. Nauk SSSR, 9, 239 (not seen; extracted from Chem- 48, 13553H). planation is that the greater size difference of Sb and Abstr., Coppens,P. and W. C. Hamilton (1970; 6ti.o,.opic extinction S compared to As and S causes more ordering within corrections in the Zachariasen approximatiot. Acta Crystallogr., ullmannite than gersdorffite, since gersdorffite has A26,7L-83. been observed in both the ordered (Bayliss and Ste- Finger, L. W. and E. Prince (1975)A systemof Fortran IV com- phenson, 1967) and disordered (Bayliss, 1968) forms, puter programsfor crystalstructure computations' National Bu- reau of Standards TechnicalNote 854. whereas ullmannite has only been observed in the or- InternationalTablesfor X-ray Crystallography,Vol. IV (1974).Ky- dered form. noch Press,Birmingham, England. Nelson,J. B. and D. P. Riley (1945)An experimentalinvestigation Acknowledgments of extrapolation methods in the derivation of accurate unit-cell dimensionsof crystals.Proc. Phys.9oc., 57, 160-177. Financial assistance was provided by the National Research Peacock,M. A. and W. G. Henry (1948)The crystal structure of Council of Canada. Mr. B. Rutherford did the electron probe (CoAsS), gersdorfrte (NiAsS), and ullmannite analysis. Dr. C. T. Prewitt critically reviewed the manuscript. (NiSbS). (Jniv. Toronto Studies,Geol. Ser., 52,7l-8O- Ramsdell,L. S. (1925)The crystal structureof somemetallic sul- References phides.Am. Mineral., 10,281-304'. Bayliss,P. (1968)The crystal structureof disorderedgersdorffite. Stout, M. Z. andP. Baytss (1975)Crystal structureof a natural ti- Am. Mineral., 53, 29V293. tanomagnetite.Can. M ineral.,1J, 86-88. - (1969)Isomorphous substitution in syntheticcobaltite and Szymariski,J. T. (1979) The crystal structure of platarsite, ullmannite. Am. Mineral., 54, 426430. Pt(As,S)r,and a comparisonwith sperrytte, PtAs2.Can. Min- - (1977a)Crystal structure refinementof arsenianullman- eral.,17, ll7-223. nite. Am. Mineral., 62,369-373. Takduchi, Y. (1957) The absolute structure of ullmanite [rt4' - (1977b) Crystal structure refinement of a weakly ani- NiSbS.Mrneral. J., 2,9{l-.102. sotropic pyrite. Am. Mineral., 62, 1168-1172. Wuensch,B. J. and C. T. Prewitt (1965)Conections for X-ray ab- - and N. C. Stephenson(1967) The crystalstructure of gers- sorption by a crystal of arbitrary shape.Z. Kristallogr.,122'2+ dorffite. Mineral. Mag., 36, 1842. 59. - and - (1968) The crystal structure of gersdorffite Zachariasen,W. H. (196?)A generaltheory of X-ray diffraction in (III), a distorted and disorderedpyrite structure.Mineral. Mag., crystals.Acta Crystallogr.,2 3, 558-564. 36, 940-947. Bokij, G. B. and L. I. Tsenokev(1954) X-ray examinationof co- Manuscipt received,MaY ll, 1979; baltite, gersdorffite and ullmannite. Trudy Inst. Kristallogr. acceptedforpublication, September l3' 1979.