Ab initio calculations of phonon spectra in ATiO3 perovskite crystals (A = Ca, Sr, Ba, Ra, Cd, Zn, Mg, Ge, Sn, Pb)

TL;DR

This study uses ab initio density functional theory to calculate phonon spectra of various ATiO3 perovskite crystals, analyzing lattice instabilities, phase energies, and ferroelectricity origins.

Contribution

It provides a comprehensive first-principles analysis of phonon spectra, lattice distortions, and ferroelectric mechanisms across multiple ATiO3 perovskites, highlighting the role of atomic size and electronic structure.

Findings

Identification of unstable phonon modes indicating possible lattice distortions.

Determination of phase energies related to lattice instabilities.

Insights into the atomic factors influencing ferroelectricity.

Abstract

The phonon spectra of calcium, strontium, barium, radium, cadmium, zinc, magnesium, germanium, tin, and lead titanates with the perovskite structure are calculated from first principles within the density functional theory. By analyzing the unstable modes in the phonon spectra, the possible lattice distortions are determined and the energies of the corresponding phases are calculated. From analyzing the phonon spectra, force constants, and eigenvectors of TO phonons, a conclusion is drawn on the origin of the ferroelectricity in considered crystals. It is shown that the main factors determining the possible off-centering of atoms in the A position are the geometric size and electronic configuration of these atoms.