Ionic conductivity, partial thermopowers, heats of transport and the Soret effect of α-Ag2+δSe -: an experimental study

The ionic and electronic partial thermopowers, the partial entropy of silver metal and the Soret effect in alpha-Ag2+deltaSe (low temperature phase) have been studied as functions of temperature and deviation delta from stoichiometry by means of a nonisothermal galvanic cell. The partial ionic conductivity has been measured to complete the information on the defect structure and properties. From a combination of the experimental data, the heat of transport Q(Ag)* of silver metal is determined. In an additional experiment, Q(Ag)*, is determined directly from a time-resolved measurement of the ionic thermopower. The measured non-isothermal transport properties are discussed in respect to the defect structure and isothermal transport properties of alpha-Ag2+deltaSe. We observe a strong composition dependence of the heat of transport Q(Ag)* which is explained by a formal analysis on the basis of linear irreversible thermodynamics. Information on the individual heats of transport of the mobile point defects is extracted.