Ferroelectric properties of RbNbO3 and RbTaO3

TL;DR

This study uses first-principles calculations to explore the ferroelectric properties and phase stability of RbNbO3 and RbTaO3, revealing the ground state structure and the suppression of ferroelectricity in RbTaO3.

Contribution

It provides detailed first-principles analysis of phonon spectra, phase structures, and ferroelectric properties of RbNbO3 and RbTaO3, including comparisons with other ferroelectric materials.

Findings

R3m is the ground-state structure of RbNbO3.

Ferroelectric instability is suppressed in RbTaO3 by zero-point vibrations.

Calculated properties of RbNbO3 are comparable to KNbO3, LiNbO3, and BaTiO3.

Abstract

Phonon spectra of cubic rubidium niobate and rubidium tantalate with the perovskite structure are calculated from first principles within the density functional theory. Based on the analysis of unstable modes in the phonon spectra, the structures of possible distorted phases are determined, their energies are calculated, and it is shown that $R3m$ is the ground-state structure of RbNbO3. In RbTaO3, the ferroelectric instability is suppressed by zero-point lattice vibrations. For ferroelectric phases of RbNbO3, spontaneous polarization, piezoelectric, nonlinear optical, electro-optical, and other properties as well as the energy band gap in the LDA and GW approximations are calculated. The properties of the rhombohedral RbNbO3 are compared with those of rhombohedral KNbO3, LiNbO3, and BaTiO3.