Ferroelectric phase transitions and three-dimensional phase diagrams of a Pb(Zr,Ti)O3 system under a hydrostatic pressure

Effects of hydrostatic pressure on various ferroelectric phase transitions in Pb(Zr,Ti)O-3 (PZT) have been investigated using the thermodynamic formalism based on the Landau-Devonshire phenomenological theory. For these purposes, the rotostrictive coefficient related to the coupling between the tilting of oxygen octahedron and the stress was evaluated first. We have then simulated three-dimensional phase diagrams of the PZT system using composition, stress and temperature as the three independent thermodynamic variables. It has been shown that, with increasing tensile hydrostatic pressure, the para-ferro transition temperature increases but the transition temperature between the two ferroelectric rhombohedral phases (F-R(HT)-F-R(LT)) decreases, and the morphotropic phase boundary moves slightly toward the tetragonal-phase field. Contrary to these, opposite tendencies are predicted under a compressive stress. The thermodynamic computation of ferroelectric properties in the vicinity of the F-R(HT)-F-R(LT) phase transition further suggests that a first-order phase transition gradually becomes a continuous second-order transition with increasing tensile stress. (C) 1999 American Institute of Physics. [S0021-8979(99)02805-4].