Ternary semiconducting compounds with sodium chloride-like structure: AgSbSe₂, AgSbTe₂, AgBiS₂, AgBiSe₂

Abstract

The high temperature modification of AgSbS%, AgSbTe 2, AgBiS~, and AgBiSe2 has a face-centered cubic statistically NaCl-type structure with Ag and Bi (or Sb) atoms distributed indistinguishably and on the average in one set of positions (0, 0, 0; 0, ½, ½; O) and the Group VI atoms distributed on the average in the other set of positions (½, ½, ½; 0, 0, ½; ~). Because it is extremely unlikely that the Ag, Bi and Sb atoms all have the same effective sizes in these compounds, at least one group of atoms (4(a) or 4(b)) must not be centered exactlyat the space group sites.For AgSbSe 2 and AgSbTe 2, the cubic structure persists at room temperature. However, in the cases of AgBiS~. and AgBiSe 2 an ordering of the Ag and Bi atoms takes place at temperatures well above room temperature. In the case of AgBiS% (on which most of the detailed work has been done), above 287 °C., the disordered NaCl-type exists; between 287 °C. and about 120 °C., a rhombohedral phase exists which belongs to space group D3d (5)-R3m with Ag in 1 (a) : (0, 0, 0), Bi in 1 (b) : ~-, ½) and Se in 2(c) : ± (x, x, x) with x ~ 0-26. The lattice constants of this phase at 240 °C. are a = 7.022 A, a ----34 ° 40". Between 120 °C. and 25 °C. (and probably lower), there is another phase. The most probable space group of this modification is Dad(3)-P3ml with three formula units per Lmit cell of dimensions a = 4.18:t:0.02, c ----19.67±0.05 A. This cell is the original triply primitive hexagonal cell on which the rhombohedral modification may be indexed but with slight additional displacements of the atoms. In particular, pairs of Ag and of Bi atoms are no longer in the most highly specialized positions, and the three pairs of Se atoms are no longer equivalent.The structure of the room temperature modification has been solved with the use of single crystal and powder X-ray diffraction data. Displacements of the atoms from the ideal positions are not large. Good agreement of calculated with observed intensities is obtained when parameters are adjusted such that the average Ag-Se and Bi-Se distances in AgBiS% are 2-83 and 3.01 A, respectively.The room temperature form of AgBiS~ is isostructural (a = 4.07+0.02, c = 19.06±0-05 A) with that of AgBiS% and presumably has an intermediate form analogous to that of AgBiSe2.

Analysis of the Influence of Thermal Treatment on the Stability of Ag1−xSb1+xTe2+x and Se-Doped AgSbTe2

“…7 They assumed that single crystals prepared by them had rock salt structure (Fm 3m), with Ag and Sb atoms distributed statistically in one of the Wyckoff positions (4a) and Te atoms occupying the second one (4b). Geller and Wernick observed that the nature of the disorder should be complicated because both type of atoms: Ag and Sb differ significantly in electronic structure, atomic radius, and other chemical properties.…”

Nanoscale clusters in the high performance thermoelectricAgPbmSbTem+2

“…The chemical component of the second phase is the same as bulk AgSbTe 2 . 19 In this model there are no Pb atoms inside the minor phase. For the minor phase of this model we tried both a chemically disordered cluster model N C0 0 with a cubic unit cell and Ag, Sb atoms distributed randomly on the lead sublattice ( Fig.…”

Cadmium substitution in miargyrite (AgSbS2) and related phases: an experimental reconnaissance

“…This high-temperature polymorph survives metastably at room temperature. Low-temperature matildite, 13-AgBiS2, is hexagonal (Geller and Wernick, 1959), while the hightemperature cubic form (confusingly called ~-AgBiS2) exists above 210~ (Hofmann, 1938;Graham, 1951). Hall (1966) synthesized three polymorphs of AgAsS2; below 320~ the rhombohedral mineral trechmannite, 7-AgAsS2, is stable Mineralogical Magazine, June 1996, Vol.…”

“…60, pp. 393-401 C~ Copyright the Mineralogical Society References: 1, tlofmann (1938); 2, Graham (1951); 3, Knowles (1964): 4, Keighin and Honea (1969); 5, Geller and Wernick (1959);6, Hall (1966);7, Roland (1968); 8, Matsumoto and Norwacki (1968).…”