THE RATIO OF RHOMBOHEDRAL AND TETRAGONAL PHASES ON THE MORPHOTROPIC PHASE-BOUNDARY IN LEAD ZIRCONATE TITANATE

A method is introduced to determine the statistical distribution of energetically degenerate but geometrically inequivalent states in a temperature induced phase transition in solids. The method has been employed to calculate the ratio of the rhombohedral and tetragonal phases in the Pb(ZrxTi1-x)O3 solid solution of the morphotropic phase boundary (MPB) composition. Our results indicate that the MPB determined by Jaffe, Cook and Jaffe [Piezoelectric Ceramics (Academic Press, London, 1971) p. 136] from structural measurements should be shifted to the rhombohedral side, which is more consistent with the MPB determined from dielectric measurements.