Dynamic Displacement Disorder of Cubic BaTiO$_3$

TL;DR

This study combines synchrotron X-ray experiments and molecular dynamics simulations to clarify the nature of diffuse scattering in cubic BaTiO$_3$, revealing that narrow diffuse sheets result from overdamped soft phonons, supporting a displacive phase transition model.

Contribution

It provides a detailed analysis linking diffuse scattering features to soft phonon dynamics in BaTiO$_3$, confirming a displacive transition mechanism.

Findings

Diffuse scattering sheets are caused by overdamped soft phonons.

The results support a displacive model of the cubic phase.

The study clarifies the disorder in paraelectric BaTiO$_3$.

Abstract

The three dimensional distribution of the X-ray diffuse scattering intensity of BaTiO$_3$ has been recorded in a synchrotron experiment and simultaneously computed using molecular dynamics simulations of a shell-model. Together these have allowed the details of the disorder in paraelectric BaTiO$_3$ to be clarified. The narrow sheets of diffuse scattering, related to the famous anisotropic longitudinal correlations of Ti ions, are shown to be caused entirely by the overdamped anharmonic soft phonon branch. This finding demonstrates that the occurrence of narrow sheets of diffuse scattering agrees with a displacive picture of the cubic phase of this textbook ferroelectric material.