Innovative Electrochemical Synthesis, Structural, and Thermodynamic Characterization of the Ag2FeGeS4 Compound in the Ag-Fe-Ge-S System
摘要
For the first time, a single-phase compound Ag2FeGeS4 has been synthesized in the central part (D section) of an electrochemical cell (ECC) of the type (1): C || Ag || SE || D || SE || Ag || C, where C is the graphite; Ag is the pure silver, and SE is the solid-state electrolyte. The crystal structure of the Ag2FeGeS4 compound was determined as: structure-type CuFeS2, space group I–42d (No 122–dba), a = 0.57077(2), c = 1.05031(4) nm, V = 0.34217(2) nm3, and Z = 2. The phase equilibria of the Ge-GeS2-FeS2-FeS-Ag2FeS2 region of the Ag-Fe-Ge-S system were established by the modified electromotive force method. For these studies and thermodynamic measurements, the ECCs (2) were assembled: (−) C || Ag || SE || R(Ag+) || PE || C (+), where PE is the positive electrode, and R(Ag+) is the diffusion region of Ag+ ions. At the stage of cell fabrication, PE is a nonequilibrium, finely dispersed, well-mixed mixture of pure silver, mono- and disulfides of iron, and germanium, with a ratio of simple substances covering the entire composite space of the investigated region. The values of the standard thermodynamic functions of the Ag2FeGeS4 compound were established for the first time.