Gibbs energy of formation of lead zirconate

Abstract

The Gibbs energy of formation of zirconia-saturated lead zirconate was determined by emf measurements on the solid state cells Pt, Ir, Pb + PbO/CaO-ZrO₂/Ni+NiO, Pt and Pt, Ir, Pb + Pb_1-xZrO_3-x+ZrO₂/CaO-ZrO₂/Ni+NiO, Pt at 800 to 1400 K. The results obtained differ significantly from those reported in the literature based on vapor-pressure measurements, using Knudsen effusion and transportation techniques and assuming that the vapor phase consisted entirely of monomeric PbO molecules. A reanalysis of the data obtained in the earlier vapor-pressure studies, using mass-spectrometric measurements on polymeric PbO species in the gas phase, gives Gibbs energies of formation of lead zirconate which are in better agreement with those obtained in this study. Recent electrochemical measurements using CaO-ZrO₂ and PbF₂ solid electrolytes are in good agreement with the present study. The results obtained in this study are also consistent with the phase diagram which shows decomposition of the zirconate to tetragonal zirconia and a liquid phase rich in PbO at 1843 K.