Thermoelectric Power of Silver Halides

Abstract

Thermoelectric power measurements have been made on the systems AgCl+CdCl2, AgBr+Ag2S, and AgBr+CdS, as well as the pure silver halides, in the temperature range from 100° to 400°C. Silver metal electrodes were used. The behavior of AgCl and CdCl2 is similar to the previously investigated AgBr+CdBr2 system, except that the effect of the impurity is more pronounced in AgCl. The results of Cd-doping of AgBr and AgCl are analyzed according to the theory of Howard and Lidiard to give the concentration of Frenkel defects, the ratio of mobilities, and the quantities qi*+qv*, qi*+Tsi′, and qv*+Tsv′, where q* and s′ are the heats of transport and entropies of formation for the interstitials and vacancies. The results are in agreement with conductivity data, but the heats of transport are surprisingly large and temperature dependent. It is concluded that association between Cd+ + and Ag+ vacancies is negligible above 100°C, but that association between S— — and Ag+ interstitials, and between Cd+ + and S— —, is significant even at 400°C.