Dielectric properties depend on the crystal structure of perovskite-type RbTaO3 synthesized at high pressure

Abstract

We successfully synthesized perovskite-type RbTaO₃ at 1173 K under 4 GPa. RbTaO₃ crystalized as a cubic system (Pmm space group (SG), a = 4.04108(3) Å) at 300 K in contrast to the orthorhombic perovskite-type RbNbO₃ prepared under the same conditions. During the cooling process, it reversibly transformed into a tetragonal phase (SG: P4mm) at 270 K, and into an orthorhombic phase (SG: Amm2) at 80 K. Corresponding to the phase transition, the relative permittivity showed a peak at 270 K with a maximum value of approximately 2000 and a kink at 80 K. This transition scheme is analogous to well-known displacement-type ferroelectrics of BaTiO₃ and KNbO₃. This is in contrast to KTaO₃, which retains a cubic system and quantum paraelectric properties at the lowest temperature.