РНYSICO-CHEMICAL INTERACTION IN Ag2S – {As, Sb, Bi}2S3 – GeS2 SYSTEMS

Abstract

Physico-chemical interactions in the Ag2S – As2S3 – GeS2, Ag2S – Sb2S3 – GeS2 and Ag2S – Bi2S3 – GeS2 systems at 500 K was investigated. Minor single-phase regions exist in the quasi-ternary system Ag2S – As2S3 – GeS2 at 500 K that are based on the initial compounds Ag2S, As2S3, GeS2 and ternary compounds of the boundary systems: Ag3AsS3, AgAsS2, Ag10Ge3S11, Ag2GeS3. The homogeneity region of Ag8GeS6 extends up to 20 mol.% along the Ag3AsS3 – Ag8GeS6 section. The existence of thirteen two-phase equilibria was found, five of which are inside the quasi-ternary system, which divide the concentration triangle into ten three-phase fields. Vertical section Sb2S3 – GeS2 was investigated in the Ag2S – Sb2S3 – GeS2 system; the section is of the eutectic type of interaction with coordinates of 35 mol. % GeS2 at 747 K (L↔α+GeS2). The formation of quaternary compounds of the compositions Ag11Sb3GeS12 and Ag8SbGe3S11 was established for the first time. The first thiosalt is formed at the intersection of AgSbS2 – Ag8GeS6 and Ag3SbS3 – Ag2GeS3; the single-phase nature of the sample of this composition was determined by scanning electron microscopy. The quaternary phase Ag8SbGe3S11 is formed at the intersection of Sb2S3 – Ag10Ge3S11 and Ag3SbS3 – Ag2GeS3. The system has minor solid solutions ranges of the original Sb2S3 and Ag2GeS3 that do not exceed 5 mol.% at the annealing temperature. The quasi-ternary system features ten single-phase regions, Ag2S, Sb2S3 (α-solid solution), GeS2, Ag3SbS3, AgSbS2, Ag8GeS6, Ag10Ge3S11, Ag2GeS3 (β-solid solution), Ag11Sb3GeS12, ~Ag23Sb3Ge7S30 and nineteen two-phase equilibria, of which eleven are inside the quasi-ternary system; together, they divide the concentration triangle into ten three-phase regions. Isothermal section of the quasi-ternary system Ag2S – Bi2S3 – GeS2 at 500 K, similarly to one with arsenic, features no new phases. Single-phase regions up to 5 mol.% based on bismuth-containing compounds Bi2S3, AgBi3S5 AgBiS2 were found. Investigated phase diagram of the Bi2S3–GeS2 system is of the eutectic type (Type V of Rooseboom classification). The eutectic coordinates are 860 K and 52 mol.% GeS2. Eight single-phase fields, Ag2S, Bi2S3 (α-solid solution), GeS2, AgBiS2 (β-solid solution), AgBi3S5 (γ-solid solution), Ag8GeS6, Ag10Ge3S11, Ag2GeS3, were found in the system under given synthesis conditions. Thirteen two-phase equilibria, five of which are inside the quasi-ternary system, separate the triangle into six three-phase fields.