Ionic Conduction and Oxygen Diffusion in Yellow Lead Oxide

Abstract

Electrical conduction in yellow lead oxide has been studied between 500° and 800°C and ionic and electronic contributions separated by means of transport and EMF techniques. The electronic conductivity depends on oxygen partial pressure and on doping. Its dependence on the oxygen pressure is markedly different for samples doped with bismuth or with potassium. It increases with pressure in K‐doped samples; approximately as P1/n with n between 4 and 6. In Bi‐doped samples a decrease is found wih n between —4 and —6. Information on ionic conduction stems mainly from transport number determinations with the EMF technique. It was found that the ionic conduction, which is carried by oxygen, is independent of the oxygen pressure and increases on the addition of bismuth. Self‐diffusion measurements of oxygen were carried out using the isotope exchange method. It was found that the exchange at the surface is too slow with oxygen gas, but a diffusion‐controlled exchange rate could be obtained with a carbon dioxide gas. The results correspond well with those given by Thompson and Strong; the self-diffusion coefficient at 787°K amounts to about 10−10 cm2/sec. Doping with bismuth increases this value, whereas an influence of potassium dope is not so evident. No influence of the oxygen pressure could be found. Although doping with bismuth causes similar changes in the ionic conductivity and in the self‐diffusion of oxygen, a quantitative comparison suggests that transport of oxygen in neutral form also makes a contribution to the diffusion.