Crystallographic Features and Tetragonal Phase Stability of PbVO₃, a New Member of PbTiO₃ Family

Abstract

Crystallographic features and stability of the tetragonal phase of PbVO3 were investigated under ambient and high pressure and compared with those of PbTiO3. PbVO3 is isotypic with PbTiO3 [at 300 K, space group P4mm; a = 3.803 91(5) Å and c = 4.676 80(8) Å, Z = 1]. Tetragonality (c/a) of PbVO3 was the largest among the PbTiO3-type compounds and increased monotonically with increasing temperature from 12 to 570 K without transition to cubic phase. The large tetragonality and the atomic position determined from synchrotron X-ray powder diffraction data suggest a large ferroelectric polarization above 100 μC/cm2. Above 570 K in air, PbVO3 was oxidized to Pb2V2O7. Application of high pressure prevented the oxidation and thus a tetragonal-to-cubic phase transition accompanied by an insulator-to-metal phase transition was observed from about 2 GPa at room temperature.