Origin of the large phonon band-gap in SrTiO3 and the vibrational signatures of ferroelectricity in ATiO3 perovskite: First principles lattice dynamics and inelastic neutron scattering of PbTiO3, BaTiO3 and SrTiO3

TL;DR

This study combines first principles calculations and neutron scattering to explore phonon spectra and bonding in SrTiO3, PbTiO3, and BaTiO3, revealing how vibrational signatures relate to ferroelectricity and quantum paraelectric behavior.

Contribution

It provides new insights into the phonon band-gap and vibrational signatures associated with ferroelectricity in ATiO3 perovskites using combined computational and experimental methods.

Findings

SrTiO3 has a large 70-90 meV phonon band-gap unlike ferroelectric counterparts.

Giant anisotropies are observed in PbTiO3's phonon dispersion and electromechanical response.

Distinct bonding characteristics correlate with vibrational signatures and ferroelectric properties.

Abstract

We report first principles density functional perturbation theory calculations and inelastic neutron scattering measurements of the phonon density of states, dispersion relations and electromechanical response of PbTiO3, BaTiO3 and SrTiO3. The phonon density-of-states of the quantum paraelectric SrTiO3 is found to be fundamentally distinct from that of ferroelectric PbTiO3 and BaTiO3 with a large 70-90 meV phonon band-gap. The phonon dispersion and electromechanical response of PbTiO3 reveal giant anisotropies. The interplay of covalent bonding and ferroelectricity, strongly modulates the electromechanical response and give rise to spectacular signatures in the phonon spectra. The computed charge densities have been used to study the bonding in these perovskites. Distinct bonding characteristics in the ferroelectric and paraelectric phases give rise to spectacular vibrational signatures. While a large phonon band-gap in ATiO3 perovskites seems a characteristic of quantum paraelectrics, anisotropy of the phonon spectra correlates well with ferroelectric strength. These correlations between the phonon spectra and ferroelectricity, can guide future efforts at custom designing still more effective piezoelectrics for applications. These results suggest that vibrational spectroscopy can help design novel materials.