Recovery of harmonic-like behaviour of the polar mode in BaTiO$_3$ at high pressure

TL;DR

This study investigates the local structural behavior of BaTiO₃ under high pressure using neutron scattering, revealing a shift towards harmonic behavior at pressures up to 4.18 GPa, contrasting with its high-temperature phase.

Contribution

It provides new insights into the pressure-induced local structural changes in BaTiO₃, highlighting a transition towards harmonic behavior not previously characterized.

Findings

High-pressure BaTiO₃ exhibits harmonic-like local structure.

Suppression of mode amplitude and isotropy at high pressure.

Loss of sensitivity to Ti displacements under pressure.

Abstract

The local structure of high pressure BaTiO$_3$ has been interrogated by neutron total scattering methods, up to pressures of 4.18 GPa at ambient temperature. Competitive refinements of cubic, tetragonal and rhombohedral distortion modes against pair distribution functions indicate contrasting local structure behaviour of temperature- and pressure-induced cubic BaTiO$_3$. Suppression of the mode amplitude, isotropy of the order parameter direction and loss of sensitivity to correlated Ti displacements at high pressure all suggest a high-pressure local structure that is more consistent with the harmonic approximation, rather than an order-disorder model which better describes high-temperature cubic BaTiO$_3$ in the vicinity of the tetragonal phase transition.