The System Cu3ass4––Cu3sbs4 and Investigations on Normal Tetrahedral Structures
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20 Z. Kristallogr. 219 (2004) 20–26 # by Oldenbourg Wissenschaftsverlag, Mu¨nchen The system Cu3AsS4––Cu3SbS4 and investigations on normal tetrahedral structures Arno Pfitzner* and Thomas Bernert Universita¨t Regensburg, Institut fu¨r Anorganische Chemie, Universita¨tsstraße 31, D-93040 Regensburg, Germany Dedicated to Professor Dr. H.-L. Keller on the occasion of his 60th birthday Received June 26, 2003; accepted August 12, 2003 X-ray diffraction / Powder diffraction structure analysis / sphalerite structure type and the hexagonal wurtzite struc- Single crystal structure analysis / Thiometallate / ture type are distinguished due to the packing of the an- Tetrahedral structures / Wurtzite structure type / Sphalerite ions. In ternary or multinary tetrahedral compounds the structure type cation positions may be occupied in an ordered or in a statistic way. An ordered distribution causes a reduction of Abstract. In order to develop a novel model to predict if symmetry, e.g. leading to a tetragonal instead of a cubic a so called normal tetrahedral compound crystallizes in a cell for Cu3SbS4 (famatinite), whereas an orthorhombic wurtzite-orsphalerite superstructure type, the system cell instead of a hexagonal cell results for Cu3AsS4 (enar- Cu3AsS4––Cu3SbS4 was reinvestigated. A solid solution gite) [2]. An even lower symmetry has been observed in series was prepared and the mixed crystals were charac- some other cases. terized by powder X-ray techniques. The crystal structures The system Cu3AsS4––Cu3SbS4 is well investigated of Cu3As0.330Sb0.670S4,Cu3As0.736Sb0.264S4, and Cu3AsS4 with respect to the formation of mixed crystals and ther- were refined from single crystal X-ray data. The re- mal properties [3, 4]. According to powder data the struc- finements converged to R ¼ 0.0209, wR2 ¼ 0.0484 ture of the mixed crystals Cu3AsxSb1ÀxS4 changes at (Cu3As0.330Sb0.670S4, 201unique reflections, 15parameters), x ¼ 0.8. For x < 0.8 the tetragonal famatinite type is ob- R ¼ 0.0235, wR2 ¼ 0.0596 (Cu3As0.736Sb0.264S4, 218 re- served, and for x > 0.8 the orthorhombic enargite type is flections, 15 parameters), and R ¼ 0.0241, wR2 ¼ 0.0669 found. Most of the former investigations concentrate on (Cu3AsS4, 721reflections, 45 parameters). Z is 2 for all the stability of the different phases in the quasi-binary sys- compounds. The volumes of the tetrahedra [MS4] were tem. Kanazawa describes the evolution of the lattice para- calculated for the investigated compounds. In addition, the meters in the solid solution series Cu3AsxSb1ÀxS4 [5]. Ber- corresponding data were calculated for further solids from nardini et al. examine the evolution of the d112-values, the literature data. The volumes of the tetrahedra are used to most intense reflection in the X-ray powder diagram. The separate compounds with a sphalerite type anion arrange- d112 spacing increases linearly from luzonite to famatinite ment from compounds with hexagonal packed anions. A [6]. Luzonite is the arsenian homologue of famatinite. closer inspection of the tetrahedra volumes reveals a great- In the literature some refinements of natural samples of er variation for one given material in the case of wurtzite enargite can be found [7–10]. However, these refinements type superstructures than for sphalerite type superstruc- cannot be used for deriving crystal chemical parameters tures. A critical difference in the tetrahedra volumes is de- since the natural samples may contain a manifold of ele- rived from these data. ments. Only Karanovic et al. determined the composition of their sample exactly by energy dispersive spectroscopy, it was Cu3.074As0.955S3.971 [10]. Introduction The crystal structure of Cu3As0.685Sb0.315S4 was deter- mined by Marumo and Nowacki in 1967 [11]. This com- Normal tetrahedral structures have been investigated for a position was reinvestigated, as their data based on film long time because of their interesting electrical and optical methods. properties. Parthe´ has given easy valence electron rules in To date it is not possible to predict which structure order to predict the composition of multinary compounds type will be formed by a normal tetrahedral compound which crystallize in tetrahedral structures [1]. The cubic with a given composition. Some authors suggest that the C cation in quaternary compounds A2BCQ4 (A ¼ Cu, B ¼ Mn, Fe, Co, Ni, Cd, C ¼ Si, Ge, Sn, Q ¼ S, Se) * Correspondence author plays an important role [12]. However, despite numerous (e-mail: [email protected]) efforts, e.g. ref. [13], there is no concept available to de- Cu3AsS4––Cu3SbS4 –– normal tetrahedral structures 21 rive at least the arrangement of the anions from simple (M ¼ Cu, As, Sb) is available. It is possible to derive crystal chemical data, e.g. ionic radii of the constituent critical volume ratios for the change from the cubic anion elements. arrangement to the hexagonal packing from these data. A novel approach to predict the preference for either a distorted hexagonal or a distorted cubic arrangement of the anions was recently described [14]. It became obvious Experimental that in Cu3PS4 (enargite type) the tetrahedra [MS4] (M ¼ Cu, P) exhibit a significant difference of their vol- Cu3AsS4 and Cu3SbS4 were prepared by annealing stoi- umes while in Cu3SbS4 the tetrahedra [MS4](M¼ Cu, chiometric mixtures of the elements in evacuated, sealed Sb) have about the same size. quartz ampoules for two weeks at 590 C. The products Herein, we report our investigations of the system were homogenized between two annealing periods. The Cu3AsxSb1ÀxS4. This system was chosen since Cu3PS4 and solid solutions Cu3AsxSb1ÀxS4 (x ¼ 0.1to 0.9) were pre- Cu3SbS4 do not form a solid solution series. Lattice con- pared from the end members by annealing stoichiometric stants and thermal behaviour of the mixed crystals are re- mixtures at 595 C for a total of four weeks. Again, the ported. In addition, selected compositions are characterized materials were ground between two annealing periods. by single crystal X-ray structure determination. Thus, a pre- After that time, no impurities were detected by X-ray cise information about the volumes of the tetrahedra [MS4] powder diffraction. a Table 1. Crystallographic data for the X-ray structure determinations of Cu3As0.3Sb0.7S4,Cu3As0.3Sb0.7S4, and Cu3AsS4. Compound Cu3As0.330Sb0.670S4 Cu3As0.736Sb0.264S4 Cu3AsS4 Formula weight/(g molÀ1) 426.56 407.83 393.78 Crystal size/mm3 0.12 0.10 0.08 0.11 0.09 0.09 0.32 0.20 0.18 Colour black black black Crystal system tetragonal tetragonal orthorhombic Space group I42m (no. 121) I42m (no. 121) Pmn21 (no. 31) Lattice constants/A a ¼ 5.353(1) a ¼ 5.315(1) a ¼ 7.399(1) c ¼ 10.652(2) c ¼ 10.536(2) b ¼ 6.428(1) c ¼ 6.145(1) Cell volume/A3, Z 305.2(1), 2 297.7(1), 2 292.3(1), 2 À3 rX-ray/(g cm ) 4.642 4.550 4.475 Diffractometer STOE IPDS, MoKa, l ¼ 0.71073 A, oriented graphite monochromator Image plate distance /mm 60 55 60 j-range/, Dj/ 0 j 112.5, 1.5 0 j 140, 2.0 0 j 173,1.0 Absorption correction Numerical, shape optimized with X-SHAPE [15] Irradiation time/image/min. 15 18 13 Temperature/C202420 2 q-range/ 3.8 < 2q < 56.3 4.2 < 2q < 58.3 6.3 < 2q < 56.0 hkl-range À6 h 6 À5 h 7 À9 h 9 À6 k 6 À6 k 7 À8 k 8 À13 l 9 À14 l 14 À7 l 8 No. of reflections, Rint. 894, 0.0408 1257, 0.0398 2276, 0.0322 No. of independent reflections 201218721 No. of parameters 15 15 45 Program SHELXL97 [16] R1(I > 2s), R1(all reflections) 0.0209, 0.0209 0.0235, 0.0235 0.0240, 0.0251 b wR(I > 2sI), wR(all reflections) 0.0484, 0.0484 0.0596, 0.0596 0.0660, 0.0664 Weighting parameter a 0.0269 0.0390 0.0445 GooF 1.083 1.138 1.094 Largest difference peaks À3 Drmax, Drmin/(e A ) 0.613, À0.630 0.739, À0.542 0.643, À0.597 a: Further details of the crystal structure investigations are available on request from the Fachinformationszentrum Karlsruhe, D-76344 Eggen- stein-Leopoldshafen (Germany) (Fax: (+49)7247-808-666 (Dr. S. Ho¨hler-Schlimm); E-mail: [email protected]), on quoting the depository numbers CSD-413348 (Cu3As0.330Sb0.670S4), CSD-413349 (Cu3As0.736Sb0.264S4), and CSD-413350 (Cu3AsS4). b: Definition of R1and wR: P sPffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi rPffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 2 2 2 2 2 kPFojÀjFck ½PwðFo À Fc Þ ½wðFo À Fc Þ 2 2 2 R1 ¼ ; wR ¼ 2 2 ; GooF ¼ nÀp ; w ¼ 1=ðs ðFo ÞþðaFoÞ Þ : jFoj ½wðFo Þ 22 A. Pfitzner and T. Bernert Thermal analyses were carried out on a Setaram TMA 92 16.18 high temperature DSC in evacuated sealed quartz ampoules (inner diameter: 2.6 mm). X-ray powder diffrac- tion data were collected in transmission setup on a STOE Stadi P equipped with CuKa1 radiation (Ge monochroma- tor, Si as an external standard) and a linear PSD detector. Single crystal X-ray diffraction data of Cu3As0.330Sb0.670S4 (Cu3As0.3Sb0.7S4), Cu3As0.736Sb0.264S4 (Cu3As0.7Sb0.3S4), and Cu3AsS4 were collected on a STOE IPDS. For all three compositions a numerical absorption correction was performed. The description of the crystal shapes was optimized with X-Shape [15]. The structures were solved by direct methods and refined against F2 [16] Fig. 1a. Tetragonal lattice parameter atet vs. the composition of the with anisotropic displacement parameters for all atoms solid solution Cu3AsxSb1-xS4. including an extinction parameter. The Flack parameter was used to check for the right setting of the non-centro- symmetric structures. It was 0.00(8) for Cu3As0.3Sb0.7S4, À0.01(5) for Cu3As0.7Sb0.3S4, and 0.07(2) for Cu3AsS4.