Vìsnik Odesʹkogo Nacìonalʹnogo Unìversitetu: Hìmìâ (Nov 2020)
SYSTEM Ag2S – SnS2 – P2S5
Abstract
The quasiternary system Ag2S – SnS2 – P2S5 is characterized by quasi-binary sections between the binary and ternary phases. The existence of solid solutions Ag7+xP1-xSnxS6 (x =0÷ 0,31) and Ag8-xSn1-xPxS6 (x = 0÷0,21) was established on the quasi-binary section Ag7PS6 – Ag8SnS6. Replacement of P atoms by a mixture of [Ag + Sn] atoms in α-solid solution leads to an increase in the lattice parameters. The replacement of Sn atoms by P atoms in the β-solid solution is accompanied by a decrease in the lattice parameters. Moreover, the character is not linear, but is described by a positive deviation from Vegard’s rule. The crystal structure of two phases Ag7.31P0.69Sn0.31S6 ( а = 10.526(1) Å, SG (No 198) P213) та Ag7.8Sn0.8P0.2S6 (а = 15.205(3) Å, b = 7.527(1) Å, c = 10.663(2) Å; SG (No 33) Pna21) which are the final compositions of solid solutions. The tetra phase Ag7.31P0.69Sn0.31S6 is formed by replacing P atoms with Sn atoms. As a result, we obtain a defective, relative to the position of the atoms P, position 4a, which is inhabited by a mixture of atoms [Ag + Sn]. The coordination environment of cations is represented by tetrahedra, monohedra and dumbbells: Ag1 has a coordinating environment of sulfur atoms in the form of a dumbbellhas [S3-Ag1-S1], Ag2 is centered in the monohedron of the triangle [2S4- Ag2-S3] ; Ag3 is coordinated into a tetrahedron [Ag3S1S2S3S4], the atoms [Ag / Sn + P] have a tetrahedral environment of sulfur atoms: {[Ag/Sn+P]S23S4}. The tetra phase Ag7.8Sn0.8P0.2S6 is formed by replacing Sn atoms with P. atoms. As a result, we obtain position 4a, in which a mixture of atoms [0.8Sn + 0.2P] is localized. The coordination environment of cations is represented by tetrahedra, monohedra and dumbbells: Ag1 has a coordination environment of four sulfur atoms [Ag1S2S4S5S6], Ag2 is centered in a tetrahedron [Ag2S1S3S5S6]; Ag3 is coordinated in a tetrahedron [Ag3S1S2S5S6], Ag4 – in a monohedron [Ag4S1S4S6], Ag5 – in a monohedron [Ag5S1S2S5], Ag6 has a tetrahedral environment of sulfur atoms [Ag6S3S4S5S6]], Ag7 is coordinated in the center of the monohedron [Ag7S3S3S6], Ag8 forms a dumbbell shape with Sulfur atoms [S3-Ag8-S5]. [Sn + P] atoms have a tetrahedral environment of Sulfur atoms {[Sn+P]S1S2S3S4}.
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