Dynamics of cubic-tetragonal phase transition in KNbO$_3$ perovskite

TL;DR

This study investigates the vibrational spectrum of KNbO$_3$ in its cubic phase, revealing coupled phonon and diffuse scattering components that evolve with temperature, shedding light on the phase transition dynamics.

Contribution

It provides new insights into the coupling between acoustic phonons and diffuse scattering components during the cubic-tetragonal phase transition in KNbO$_3$.

Findings

Identification of two diffuse scattering components with different origins.

Evidence of coupling between quasi-elastic scattering and acoustic phonons.

Growth of susceptibility near the transition temperature T$_C$.

Abstract

The low-energy part of the vibration spectrum in KNbO$_3$ was studied by cold neutron inelastic scattering in the cubic phase. In addition to acoustic phonons, we observe strong diffuse scattering, which consists of two components. The first one is quasi-static and has a temperature-independent intensity. The second component appears as quasi-elastic scattering in the neutron spectrum indicating a dynamic origin. From analysis of the inelastic data we conclude that the quasi-elastic component and the acoustic phonon are mutually coupled. The susceptibility associated with the quasi-elastic component grows as the temperature approaches T$_C$.