Electrochemical and Thermodynamic Studies on Copper-Silver-Selenium System

With the help of coulometric titrations, using the solid state galvanic cell Ag/AgI/(Cu,Ag)2+δSe/C, in the temperature region between 200 and 350°C, the following parameters: Point defect concentrations, effective mass of electrons and holes, width of band gap and the partial molar thermodynamic quantities of dissolution of one mole of silver in the mixed selenide were determined as a function of the metal/selenium 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 mixed selenide by the dissolution of silver, go into the conduction band (excess of metal) or. by destruction of electron-holes into the valence band (deficit of metal). The band gap energy in the Ag1.188Cu0.812Se is 0.12 eV.