Structure and bonding in PbZrO 3 –PbTiO 3 (PZT) alloys

Abstract

Alloys of PbZrO₃–PbT iO₃ (PZT) exhibit a complex series of ferroic lattice instabilities that depend on the Zr/Ti ratio and give rise to exceptional pyroelectric and piezoelectric properties. An approach based on energetics and crystal chemical systematics is discussed that relates structure and bonding in PZT to its subsolidus phase diagram. Heats of formation, heat contents and contributions to lattice energies across the phase diagram are correlated with the perovskite tolerance factor and with displacements of Pb and (Zr, Ti) cations f rom their high symmetry positions. It is shown that at 973 K the cubic phase contains precursors of the lattice instabilities and the differing displacements of Ti and Zr inferred for the lower symmetry phases at lower temperatures. Modulations in local structure, revealed in the ratio of Pb to (Zr, Ti) cation displacements, are related to the transition temperature from the paraelectric cubic phase to the ferroic phases.