The electrical properties of molten AgX-Ag2Se (X = Br, I) mixtures

The electrical conductivity, sigma, and thermopower, S, of molten (AgX)(1-c )(Ag2Se)(c) mixtures (X = Br,I) have been measured as a function of tempera ture. The conductivity of the mixture is observed to decrease rapidly on th e addition of AgX to Ag2Se and reaches a minimum on the AgX side. The therm opower on the Ag2Se side decreases gradually as the concentration of AgX in creases until c = similar to 0.4 at which point there is rapid change to la rge positive thermopowers. The value of S(+325 mu V K-1 (AgBr), +420 mu V K -1 (AgI)) on the AgX rich side decreases rapidly on addition of Ag2Se with the result that a minimum value of S(similar to -125 mu V K-1) is observed at the composition c = similar to 0.4 in both mixtures. A discussion of the se results is presented in terms of the change from predominantly electroni c transport in liquid Ag2Se to the predominantly ionic transport in AgX. Th e increasing importance of the contribution of the inhomogeneous thermopowe r to the total thermopower of the salt rich compositions is also discussed. The decrease in the electronic conductivity with composition for c greater than or equal to 0.6 is analysed in terms of the Kubo-Greenwood equations.