Thermodynamic Studies on Beta-Silver Sulfide

From the measurement of the emf of the solid-state galvanic cell: Pt/Ag/AgI/β-Ag2+δS/Pt, and its temperature dependence the following results for different Ag/S ratios in the temperature range between 200 and 350°C are obtained: the partial molar thermodynamic quantities of dissolution of one mole of silver into the compound, point defect concentrations and the width of band gap were determined as a function of the metal/sulfur ratio. The change of the thermodynamic quantities with the change of the stoichiometric composition can be explained by varying contributions of electrons and electron-holes depending on the fact whether the electrons, which are brought into the compound by the dissolution of silver, go into the conduction band (excess of metal) or, by annihilation of electron-holes into the valence band (deficit of metal). From the electrochemical measurements besides of other quantities – the band gap energy can be calculated and is of about 0.38 eV.