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Chemical and Electronic Spectral Studies of Ullmannite (Ni4sb4s4)

Chemical and Electronic Spectral Studies of Ullmannite (Ni4sb4s4)

Indian Journal of Engineering & Materials Sciences Vol. 7, October-December 2000, pp. 459-460

Chemical and electronic spectral studies of (Ni4Sb4S4)

S N Redd/ , R V S S N Ravikumar", B J Reddy" & Y PRedd y" "Spectroscopy Laboratories, Department of Physics, SV Uni versity College, Tirupati 517 502, India bDepartment of Physics, SV Degree College, Cuddapah 516 003, India Receil'ed 25 February 2000; accepted 18 September 2000

The streak grayi sh black coloured and almost opaque ullmannite belongin g to France received from Musee De Mineralogie, Ecole Natl e, Supre Des Mines, Pari s, France, has been investi gated by atomic absorption spectroscopy (AAS) an d optical absorpti on spectroscopy. The AAS analysis shows th at the mineral contain s the transition elements (1. 14%), (0.29%), (0.073%), copper (0.013%), and manganese (0.003 1%) . The bands observed at 25967, 24993. 21546. 14966, 12252 and 86 1 8 em- I in the optical absorpti on spectrum recorded at room temperature are assigned to different transiti ons of Ni(lI) ion. The foll owing crystal fi eld parameters are evalu ated: Dq =860 em- I. B = 840 em- I, and I C= 3350 cm- , respectively. These values confirm the octahedral sy mmetry for Ni (lI) in the mineral ullman nite.

Ullmannite Ni 4Sb4S4 has a pyrite type crystal l 7 3F ~ 3TI g (F) + 3T 2g (F) + 3A 2g (F) structure - . It is essentially a -antimonide of nickel with cobalt and small amounts of iron 3 p~ 3T l g (P) substituting for nickel in addition to and 'D~ IT2g (0)+ lEg (D) bi smuth substituting for antimon/. It is cubic with IG~ ITlg (G)+ I T 2g (G)+ lEg (G)+ IAl g(G) space group P2 13. In ullminnite, the four metal atoms IS~ 9 IAl g (S) (Ni) occupy similar atomic positions • Of the eight non metal atoms (4Sb + 4S), the four Sb atoms are Of these crystal field terms, 3A 2g (F) is the ground oriented in one set of four atomic positions on the state. In octahedral symmetry, three spin allowed three fold axes and the four S atoms are ordered in the transitions expected for Ni (II) ion are: other set of four atomic positions on the three fold 3A2g (F) -7 3TI g (P) axes. The order and reduction in symmetry from Pa3 3A (F) -7 3TI g (F) to P2 13 all ow each set of four atoms to move along 2g the three fold axes. The lower symmetry of cubic 3A 2g (F) -7 3T 2g (F) space group P2 3 is shown by the absence of the 010 1 These transitions are governed by the approximate reflection and the presence of the 011 reflection 10. linear equations 10, as given by: The cubic unit cell dimensions are equal and li e between 5.88 and 5.93 A. The present studies are 3A2g (F)-7 3 Tlg( P)~ 15 Dq+ 13.5 B=vl aimed at identifying the presence of transition metal 3A2g (F)-7 3 Tl g (F)~ IS Dq+ 1.5 B =V2 ions and to confirm their coordination. 3A 2g (F) -7 3T 2g (F) ~ 10 Dq =V 3 Experimental Procedure In addition to the above, some weak spin forbidden The streak grayish black coloured and almost bands are also possible as a result of these transi ti ons. opaque mineral ullmannite is powdered nicely, mixed with nujol and its paste prepared. A thin layer of the Results and Discussion paste is taken between two thin quartz plates and its Chemical composition optical absorption spectrum recorded in the region The chemical analysis of the mineral ullmannite is 350-1 200 nm on Varian Cary-2390 spectrophotometer. carried out by AAS employing Perkins Elmer Model Theory 2380 spectrophotometer with monitorch. The analysis The Ni (II ) ion with d8 configuration gives rise to shows that the mineral contains the transition 3 F, 3P, ID, IG. and IS terms of which 3F is the ground elements having concentration: nickel (1.14%), iron slale. In a cubic ~rysta l field, these terms transform as (0.29%), cobalt (0.073%), copper (0.013%) and follows: manganese (0.003 1 %). Of th ese elements, nickel 460 INDIAN J.ENO. MATER. SCI.. OCTOBER-DECEMBER 2000

Table I-Observed and calculated band energies with their assignments ~ 8 0.6 :l! ~ If ;:,, Transition from Observed band Eositions Calculated band ~ the ground state Wavelength Wave numbe r positi ons ;;; 3 (F) (cm- ') (cm-') > A2g (nm) 2 I 'J; 'T, g(O) 385 25967 25380 <;

tll 0 -3 3T' g( p) 400 24993 24269(v,) v ;f," 'T2gCD) 464 21546 2 11 95 a: 0 ~ 3T'g(F ) 668 14966 141 33(v2) «~ I '£g( D) 8 16 12252 12962 3T2g(F) 1160 86 18 8600(V3) LOO 500 600 700 BOO 900 1000 1100 1200 WAVELENGTH (nrn) Conclusions Fig. I-Room temperature opti cal absorpti on spectrum of the The optical absorption spectrum indicates the ullmannite mineral presence of nickel in octahedral symmetry. Spectral appears to be in considerabl e quantity and the others features of no other transition metal ion are observed. in traces. This supports the relatively higher concentration of nickel in th e AAS investigati on. Optical absorption spectrum The optical absorption spectrum of ullmannite Acknowledgements mineral recorded at room temperature in UV-VlS­ Sincere thanks to Prof. C Guillemin, Professor of NIR region is shown in Fig. I . Three broad bands at , Musee De Mineralogie, Ecole Natle, 24993 cm- I (400 nm), 14966 cm- I (668 nm) and 86 18 Supre Des Mines, Paris, France, for supplying the cm- I ( 1160 nm) and three weak bands at 25967 cm- I mineral ullmannite. One of the authors, S N Reddy is (385 nm), 21546 cm- I (464 nm) and 12252 cm- I (816 grateful to Shri A G Reddy, Principal, SV Degree nm) are observed in the spectrum. All these bands are College, Cuddapah, fo r granting permIssIOn to the characteristic of Ni(II) ion in octahedral continue the research programme at SV Universi ty , I symmetryl!. 12. The broad bands at 24993 cm- (VI)' Tirupati. 14966 cm- I (V2) and 8618 cm- I (V3) are assigned to References the spi n all owed transitions from th e ground state 3 A2g I Ramdell L S,AIII Millral, 10 (1925) 281. (F) to 3TI g (P), 3TI g (F) and 3T2g (F) states, 2 Peacock M A & Henry W 0, Ulliv Toro/llo SllIdies Ceol Ser, respectively. The other weak bands are assigned to the 52 (1948) 7 1. corresponding spin forbidden transitions with the help 3 Bokii 0 B & T sinober L I, Trudy IlIsl KriSI Akad NOllk SSSR. 9 (1954) 239 (in Russ). of Tanabe-Sugano diagram 13. The approximate valu es 4 Takeuchi Y, Mill eral J, 2 (1957) 90. of Dq and B are calcul ated from the linear equations as 5 Pratt J L Y & Bayli ss P, Alii Milleral, 65 ( 1980) 154. I I Dq = 862 cm- and B = 836 cm- . Based on these 6 Peter Bayli ss, Call Milleral, 24 (1986) 27. assignments, the energy matrices for ci8 configuration 7 Rene T M. Dobbe C. Ca ll Mill eral, 29 ( 1991) 199. 8 Palache C, Berrman H & Frondel C, The systelll of are solved for different values of DC(, Band C around lII ill eralogy. Vol VII, I"~ £dll (John Wiley & Sons. New the approxi mate values evalu ated from th e linear York), 1976. I equati ons. The fo llowing values of Dq =860 cm- , 9 Tossel J A, Vaughanm 0 J & Burdett J K, Phy Chelll B=840 cm- I and C = 3350 cm- I give good fi t of the Millerals, 7 (198 1) 177. 10 Wood B J, Am Mill, 59 ( 1974) 244. experimental and calculated values of band heads. 11 Liehr A 0 & Ball Hausen C J. A IIII Phys. 6 ( 1959) 134. The observed and th e calcul ated band energies and 12 Low W, Phys Rev, 109 (1958) 274. their assignments are depicted in Table I. 13 Tanabe Y & Sugano S. J Phys Soc Japall. 9 (1954) 753.

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