Canadian Minerologist Vol. 14 w. 529-535 (1976)

THE GRYSTALSTRUCTURE OF MAWSONITE, Gu.Fe,SnS'

J. T. SZYMANSKI Mineral Sciences Laboratory, CANMET, Department ol EnergX, Mittes and Resoutces 555 Booth Street, Qtr6tta, Canada

A.rsrnecr INtnoPucrroN

The of mawsonite, Cu6FesSnS6, Mawsonite, CudFeaSnSe,was first described has been determined and refined to an R-value of by Markham & Lawrence (1965)' and idedified 0.049 (all 1426 d^ta) and 0.037 (1004 "observed" by them as being present in the material de- data only) from multiple sets of four-circle diffrac- scribed as "orange " by Murdock (1916). tometer X-ray intensity data. Microprobe analysis The chemical composition has been variously indicates that the fonnula is stoichiometric in terms reported as CuzFeaSnSro(Marlfiam & Lawrence of tlre metals, but with l.SVo of tbe replaced 1965), 1967)' C\reFea by selenium in the specimen examined. The struc- Cus.urFer.eeSno.ssSe.soS-6vy ture is tetragonal, a 7.603(2), c 5.358(1)4, space SnSa (Springer 1968), and Cu:.aoFeSno.ssSe.oo (Kachalovskaya 1973). The more lecent group P4m2, based ccp sulfur et al, and is on a nearly & matrix with metals filling hall of the tetrahedral analysesof Petruk (1973) and of Yamanaka interstices and an extra interstitial Fe atom at the Kato (1976) are in agreement with the present (Yz,Vz,/z) position. The latter gives rise- to close analyses and with the present structural deter- Fe Fe . . . Fe contacts (2.679(1)A) in the mination. z direction, but no close Fe . . . Fe contacts normal Mawsonite powder ,patterns generally have to tbis. The deviations from an ideal ccp structure been indexed on a pseudo-cubic cell, a L0.74! are due to the large Sn atorn at the origin, and r/z,Yz,Yz. .014, but becauseof its anisotropic optical prop- the extra Fe atom at The bond lengths, (Mark- angles and thermal parameters are in close agree- erties, mawsonite cannot be truly cubic ment with those found in , Cug(FeZn)SnSa, ham & Lawrence 1965). Recently, Yamanaka and kesterite, CudZn,Fe)SnSr. & Kato (1976) have indexed the mawsonite P1tr tern usins a tetragonalcell. a 1O.745,c I0.7llA. Sorvrtvrens Structu-ral exiittination' of mawsonite was in our laboratory, to provide ac- La structure cristalline de la mawsonite, undertaken Cu6Fe2SnS6,a 6t6 ddtermin€e et affin6e jusqu I un curate information on a metal-rich -- indice R de 0.049 (pour toutes les 1426 donn6es) , for comparison with the et de 0.037 (pour les 1004 donn6es "observ6es", related non metal-rich minerals, stannite and seulement) au moyen de plusieurs s6ries de don- kesterite (Ilall et al, 1975), in the same way n6es d'intensit6 recueillies sur diffractomdtre aux that the series of minerals was rayons X i quatre cercles. L'analyse i la microsonde investigated (Hall 1975). In the latter series, indique que la formule est stoechiom6trigue en ce two metal-rich copper-iron sulfides, haycockite, qui que concerne les m6taux, mais 1.57o du soufie CuoFesSr,and mooihoekite, CueFee'Sre,w€fe both cotrtenu dans 1'6chantillon 6tudi6 est remplace par iron atoms filling additional du s6l6nium. La structure est t6tragonale, a 7.603(8), believed to have tetrahedral interstices,though it was difficult to c 5.358(1)A, dans le groupe spatial fim2; eTle cot- prove It was hoped that the siste en un assemblage quasi-cubique compact d'a- this unequivocally. tomes de soufre, dont les interstices t6tra6driques present investigation would indicate more clearly sont remplis pour moiti6 par les m6taux tandis the preference of iron over copper to occupy qu'un atome de fer suppldmentaire est interstitiel additional interstitial sites. en position (r/z,Yz,r/z'). Celui-ci donne lieu I de (2.679(l)A) courtes distances Fe . Fe . . . Fe ExPERTMENTAL dans la direction z, mais non perpendiculairement a cette direction. La structure s'6carte de la struc- Three single-crystal fragments of mawsonite ture id6ale i empilement cubique compact; deux were successively examined by microprobe atomes en sont la cause: le gros atome Sn,i I'origine 1/2,/z analysisand crystal structure determination. The et l'atome Fe en ,r/2. I.es valeurs des longueurs first two fragments proved to be too small for de liaison, angles des parambtres thermiques des et parameter concordent avec celles que I'on observe dans la an accurate refinement, though the stannite Cuz(Fe,Zn)SnSaet la kest6rite Cu{Zn,Fe) structure was solved using these dat4. The re- SnS,. sults of the third crystal structure determination, 529

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IABLEI. !4ICROPROBEA}IAlYSTs FOR I4AI{SONIIE TABLE2. CRYSTALDATA FoR l4Al,llsol{ITi, Cu6Fe2SnSs

Elemt (mlcrtpmbe glven in Tabie l) speciren I Speciren 2 Speclmn 3 conposition: analysjs

ldt.l Fomla ldt.% Foru'la I'lt.% Forola Source: (ldd Creek mine, Tinmlns, ontario 868.1 LU 43.2 5.89 4?.8 5.89 44.0 6.02 Fomula welght: '13.8 Sn I .01 13.8 1.01 13.7 l.0l : tetragonal Fe l3.l 2.02 13.0 2.03 12.9 2.02 systenatlc absences: none 29.8 8.07 29.2 7.95 ?8.8 7.83 Se 1.0 0.lt l.l 0.12 space group: (possibly) P422({891,P4m(*99), PA?rG1I1), P4nZ(#'l'l 51, P4/ m (#123) Total 99.9 100.5 P4nl2.(1115)confimd by structure analysis. Specl@n l. Hotukoveln, Kanaga*I Klnomlne, Hyogo Prefecture, - - Japon(Sol tisonlan Instl tute, SpEfu n rl 22102). Celt dtrensions: a 7.603(2), c 5.358(l)A at zO'Cusing Specluens2r 3: Kldd Creeknlne, Tlmlns, ont8rlo. r(Morol) - 0.709264 Llnear absorptlon coefflcient: lj(t'lorc) ' 160.3 cm-]

on a mawsonite specimen from the Kidd Creek Denslty: rcalc - 4.659/cm-3iz' l mine, Timmins, Ontario, are reported here. (Density not rEasured) The microprobe analyses for the three maw- sonite specimens examined are listed in Table L. measured afrter The second and third were found to have a scan time. Three standards were a check on small but significant quantity of selenium re- every 50 reflections to maintain stability. A placing sulfur. This appears to be the first es- crystal alignment and instrument 4Vo of. tablished ocqurence of selenium in mawsonite. uniforrn systematic decrease of about was noted over The third specimen of mawsonite, after ex- the intensity of the standards as the crystal traction from a polished section, was cut with the period of data collection, and at the a knife, to provide more regular "faces" so as alignment was found to be unchanged procedure was applied to to facilitate subsequent absorption corrections. end, a linear scaling The resultant fragment was an irregular hexa- the data to account for this decrease. were applied to the gonal tablet 0.3X0.2X0.005 mm. Gandolfi Absorption corrections integration powder photographs of the single crystal were intensity data using a Gaussian the same as those previously published for maw- procedure, and the five equivalent segments sonite (Markham & Lawrence 1965), and con- were averaged and reduced to a single data intensi- tained no additional lines that could be attri- set which contained 1426 rndependent ob- buted to impurities. ties, of which 1004 can be considered as served at the LO% significance level, i.e. The crystal was mounted on a four-circle 1(net)21.65a(4.'fhe discrepancyfactor Cf,Af/ automatic diffractometer in a general orienta- among the five data sets was 0.031. tion. The cell dimensionswere determined from X4 a least-squares refinement of the 20, 1 and co Srnucrune Sor-urroN AND REFINEMBI{r angles @using 1970) for 90 reflections in tle range 55"q20<93". The parameterswere re- Examination of the cell dimensions suggested fined on a triclinic cell. The difference betweeu that the structure was based on two - the a and 6 cell edgeswas less than 0.2cr, and tvpe 5.3A "cubes". with the tetragonal cell di- the maximum deviation from orthogonality was mi:nsion a, representingthe face diagonal of 'ocube". less than It of arc. The errors quoted in the the This reasoning imposed the condi- Table 2 represent 3cr as derived from the least- tion that the nearly ccp sulfur lattice would be squaresmatrix. Long-exposureprecession photo- approximately c-centred and would have Z sym- graphs, and diffractometer traces of weak axial metry about the c-axis (and hence about a line reflections showed that there were no systematic through the mid-point of the c-face). An added absences. Comparison of absorption-corrected condition for limiting the choice of spacegroup intensities of symmetry-related reflections was that, based upon the probable value of showed that the Laue symmetry of the lattice Z=t (i.e. one formula unit per unit cell to as- was 4/mmm and not 4/m. count for a reasonablevalue of D"n"), the space Five Friedel-equivalent segments of data, each group chosenwould have to have a site with an l/L6 of. the Ewald sphere, were collected using equivalent-position multiplicity of 1, where tin monochromatized MoKa radiation to a limit of could be assigned. Examination of the seven 2A=12O". The scan range was 1.9o plus the possible space groups for equivalent position cr-cvz dispersion, and the background counts sites that would yield an approximately ccp were measured on either side of the peak for sulfur lattice with normal S . . . S distances of a total time approximately equal to the average about 3.8A, etminated all exceptP4m2, and this

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choice led to a successfulsolution of the struc- ple. The anomalous scattering was also modi- ture. fied to take this into account. The resultant im- The sulfur atoms were assigned to sites 4j provement in the agreement factor was 0.001, (-/+00,*Y+) and 4k (n/+,Yz,nV+) and various but it appears to be significant. In the least- combinations were tried in assigning the metals squares prosedure, refinement using unit weights to the tetrahedral interstices of the sulfur ma- and calculated weights was tried, (calculated - trix. The tin atom was arbitrarily assigned to weight l/d(F), where a(F) is based on the the origin, and an "ayerage" metal (7aCu* relative agreement of the five observations of TeFe) was assigned to fill the tetrahedral va- the intensity and on counting statistics. No srg- canciesat sites 4i (-/4,e/a,r/z), 29 (0,V2,-0) nificant difference was observed between these and 1D (Vz,t/z,O).This model refined success- refinements, and the results quoted are based fully, but the difference synthesis indicated that on the unit-weight refinempnt. an extra interstitial atom was required at site The calculations were carried out using tle Lc:(Vz,/z,Vz). Bearing in mind the multiplicities X-ray system of programs (Stewart et al. 1972). of these sites and the stoichiometrv of the for- The bond lengths and angles are given in Table muld (6Cu12Fe), site 4i was asrignia as copper. 4. The observed (10XFJ and calculated This left two copper and two iron atoms to be (10XFJ structure factors are given in Table 5*, assignedto the four sites 29, 16 and lc. Better for the refinement treating all data as "ob- agreement was observed when copper was served", though reflections which san be con- placed at .site 29 and. two iron atoms at sites sidered "unobseryed" (see above) are marked lb and lc, than when the metal types were with an asterisk. reversed. The final correct model refined anisotropic- DrscnrpttoN oF THESTRUcTURE AND DlscussloN ally to R=0.037 for the 1004 observed reflec- tions (seeabove) and to R:0.049 when all 1426 The structure of mawsonite is basedupon the were treated as observed. There was no signi- compounding of two sphalerite-like cubes (Fig. ficant difference in the final pax4meters be- l). Kesterite and stannite (Ilall & Stewart 1975) tween these two refinements, and the parame- also have "two cube" strucfures, but in these ters quoted in Table 3 are those for the latter the doubling of tle cell occurs along the z{i. case. An isotropic extinction parameter (Larsen rection. In mawsonitej the expansion is accom- 1970) was included in the refinement. The plished by considering the face diagonals of scattering curyes used were those for the neutral two adjacent sphalerite-Iike cubes as the at az atomic species Cu,Fe,Sn,Seand S, taken from directions of the tetragonal cell. The sulfur Cromer & Mann (1968) and the anomalous dis- matrix is approximately cubic close-packed, persion corrections were those of Cromer & wilh metal atoms occupying half of the avail- Libermann (L97O). Better agreement was ob- able tetrahedral interstices, and an additional tained using the curves for the neutral atomic metal atom (Fe2) occupying the interstice at species than for the ionized species. This is the (Vz,/2,1/z) position of the cell. This results opposite to what was found in the refinement in a coordination scheme in which each metal of chalcopyrite (Ilall & Stewart 1973), but the is in contact with four sulfur atoms @ig. 2, a-e), same as that found in the refinements of stan- nite and kesterite (Ilall & Stewart 1975). In the *Table final 5 is availablq at a nominal charge, from stages of refinement, a composite cufve the Depository (0.9851s of Unpublished Data, CISfi, Na- 0.0151s")was used to account for the tional Research Council of Canada, Ottawa, Can- 1.57o selenium replacementof sulfur in the sam- ada. KIA 0S2.

TASIE3. ATOI.IICPOSITIOML AXD THERI4AL PARAIiIFTERS. The anisotrcplc t€nperature factors are expressedln the fom T- exp t-2n2(ulla"2h2+ 2u.,ra*b*hk+...1, and the valuesquoted are x 104.

Aton x z uil uzz U:: utz ut: uzs 6(equlv.)

5n lq 0 0 0 84(l ) 84(l ) el(1) 0 0 0 0.68 '| Cul 29 0.0002(6) r65(3) 247(4) 86(3) 0 0 0 I .57 '165(1) 't2(4'l CuZ 4i. 0.2463(r ) 1.2463(l ) l6s(r) 182(2) -27(21 -t2(4) tel 1b I T 114(2 ) 1r4(2) 51(2) 0 0 0 0.73 Fe2 1e I * 83(2) 83(2) 54(2) 0 0 0 0.58 A1 0.2615(2) 0 0.2538(3) e5(3) t06(3) rr 5(4) 0 -26(3) 0 0.83 s2 4k 0.2597(2t 0.2490(2) e2(3) 132(4) e4(3) 0 -r8(3) 0.81

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TABLE4. BONODISTAI.ICES AIID ATGLES IIIIH STAI1DARDDEVIATIOHS ordinating sulfur atoms (S2) in a distorted tetxa- of. 2.269lr (Fig. 2e), and (a) (l) (d) BondAngles (") hedron at a distance Bonddisranes has six metal atoms at close distances. The Fel sn -Sl 2.4090) sl -Sn -Sl9 1U.26(5) -sn -sl?3 'r08.59(3) LUI - 5l 2.266(21 sl below it at 2.6794, Cul - 52 2,W(2) Sl -Cul-Sl, 106.30(r3) atom is directly above and Cu2- sl 2.293(l) sl -cul-s223 r09.63(3) and four Cu2 atoms at 2.728l. complete the Cu2- 52 2.354(l) 5223-Cul-5228ilr.85(13) Fel - 52 ?.262(1) Sl -Cu2-s2^^109.78(s) flattened octahedron of metal nearest-neighbors. Fe2- 52 2.269(1)

v-1lz

Frc. 1. Tbe unit cell of ntawsonite. Thermal ellipsoids are drawn to include 99% probabihty,

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FIG.2A

SI7 I s2?2 s225

t-____ s228 f LIJ, ZE 6223 FIG.2E sl22

FIIJ, ZL Frc. 2. Metal-sulfur coordination tetrahedra: (A) around Sn; (B) around C\rl; (C) around Cu2; (D) around Fel; (E) around Fe2; (on page opposite): sulfur-metal coordination polyhedra; @) around Sl; (c) around S2.

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The Sn S bond length QAO9A) is very close to those found in stannite QALIA) and kesterite (2.408A) (Hall er al. 1975) and is much larger than anv of the other metal-sulfur distances in the structure. The sulfur atoms are moved away from tin much more in the r-y plane than in the zdirection, and this results in a "flattened" tetrahedron, with the S1-S1.S1' angle opened up to 111.26o, and the Sl-Sn-Sls angle com- pressed to 108.59o from the ideal value of 109.47". The thermal parameters for all the atoms are in close agreement with those found in stannite and kesterite, and follow the general patteg observed in the chalcopyrite series [B(Cu)18 (Fe)1, except that the magnitudes of A(Fe) ob- served here are less than in the chalcopyrite series. This is probably due to the "crowding" occurring around the centre of the mawsonite Cu2 cell. This factor also explains why T(Fe2) and a(cozl are less than 7-@el) and 4Cul) re- spectively. The cell parameters obtained in this work la 7.603Q), c 5.358(1)Al are slightly, but not significantly larger than the reduced cell of Yamanaka & Kato (1976); a 7.598(I), c 5.355 (3)A. It is probable that the selenium replace- ment of some sulfur in the present mawsonite specimen results in the fractionally larger cell rrafameters.

POWDBR DTTT.NECTTON PATTERN Long-exposure Gandolfi single-crystal powder photographs were obtained for the crystal used in the structure determination. After the struc- ture was solved and refined, the computer pro- interaction in the e-direction to occur, probably gram POWGEN (Hall & Szymairski 1975) was via the nearest sulfur atoms (S2). However, run. This program calculates the X-ray powder such a -Fe-S-Fe-S- interaction can only be one- pattern using either the observed or the calsu- dimensional in the case of mawsonite as the dis- lated single-crystal intensities, for either a speci- tance between the iton "chains" is too large fic wavelength or combination of wavelengths. (?.603A). Similar one-dimensional systems are The Gandolfi pattern was compared to tle known, e.g., CsCoCls.2HO and RbFeSL; the calculated pattern, and excellent agreementwas latter has inter- and intra-chain distances very found. close to those found in mawsonite, and both However, serious discrepaucieswere observed CsCoClg.2II:O and RbFeCt have very low between thesetwo patterns and the recently pub- N6el temperatures. lished mawsonite powder pattern of Yamanaka The deviations of the coordination tetrahedra & Kato (1976). Their lines observed at d.=7-60 from ideal geometry can be accounted for in (hkl:l}}), 2.461(102) and 1.319(104) have terms of two factors: (1) the additional iron such weak calculated and observed single-crys- metal at the (Vz,Vz,/z) position results in some tal intensities that they should not have been degree of 'ocrowding" around the five-coor- observable.Their line at d=1.3O2(512) is too dinate 52 atom, with consequent distortions of strong to be due to mawsonite alone, and also, all angles involving S2;; Q) the larger tin atom their line at d-3,388, which was not observed at the origin gives rise to a displacement of the on the Gandolfi filns, cannot be indexed using eoordinating sulfurs away from this position. tle true mawsonite cell. It seems that despite

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their careful purification procedures, their maw- & Rowr.ero, I. F. (1973): The crystal sonite specimen may have contained extraneous structure of synthetic mooihoekite, C$Fer$c. material. Acta Cryst. B.29,2365-2372, (1975): Table 6 gives the X-ray powder pattern for & Szvl,re*srr, J. T. Paper F13, patterD generation from single crystal mawsonite obtained from the single-qyr1r1 o6- Powder data. Winter Meet. Amer. Cryst. Assoc., Char- served intensities. lottesville, Va. , Krssrrr,S. A. & STBwART,I. M. (1975): TABLE6. X-RAYPoIIDER PAIIERN 0F l4AllSoNlIECALCULAIED FOR corc RAOIATIONFROI'{ OBSERVED SINGLE-CRYSTAL DIFFRACIOI{ETER Paper 04.1-24, Stannite and kesterite: distinct TNTTNSITIES minerals or componentsof a solid solution. Aclc a(A) rca.lc hkt d(A) rcalc ,i

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