Strong Influence of the diffuse component on the lattice dynamics in Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$

TL;DR

This study investigates how the diffuse scattering component influences lattice dynamics in Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$, revealing strong coupling effects that vary across different Brillouin zones and impact the interpretation of phonon behavior.

Contribution

It demonstrates the significant influence of diffuse scattering on lattice dynamics and highlights the zone-dependent coupling effects in Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$, providing new insights into its phonon behavior.

Findings

Weak diffuse component zones show coupled harmonic oscillator dynamics.

Strong diffuse component zones exhibit strong coupling between diffuse and acoustic modes.

Coupling to the central peak explains conflicting interpretations of lattice dynamics.

Abstract

The temperature and zone dependence of the lattice dynamics in Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$ is characterized using neutron inelastic scattering. A strong correlation between the diffuse and phonon scattering is measured. The lattice dynamics in Brillouin zones where the diffuse scattering is strong is observed to display qualitatively different behavior than those zones where the diffuse scattering is weak. In the (220) and (200) zones, where there is a weak diffuse component, the dynamics are well described by coupled harmonic oscillators. Compared with SrTiO$_{3}$, the coupling is weak and isotropic, resulting in only a small transfer of spectral weight from one mode to another. A comparison of the scattering in these zones to the (110) zone, where a strong diffuse component is present, reveals a strong coupling of the diffuse (or central) component to the acoustic mode. We speculate that the coupling to the central peak is the reason for several recent conflicting interpretations of the lattice dynamics based on data from zones with a strong diffuse component.