Direct evidence of soft mode behavior near the Burns' temperature in PbMg$_{1 / 3}$Nb$_{2 / 3}$O$_{3}$ (PMN) relaxor ferroectric

TL;DR

This study provides direct neutron scattering evidence of the soft mode behavior in PMN relaxor ferroelectric near the Burns temperature, linking phonon dynamics with dielectric properties.

Contribution

It offers the first direct observation of the soft mode in PMN near the Burns temperature using inelastic neutron scattering, confirming theoretical models.

Findings

Soft mode frequency exhibits a minimum near 650K.

Results align with previous estimates of soft mode parameters.

Supports the coupling model of soft and transverse optic modes.

Abstract

Inelastic neutron scattering measurements of the relaxor ferroelectric PbMg$_{1 / 3}$Nb$_{2 / 3}$O$_{3}$ (PMN) in the temperature range 490~K$<$T$<$880~K directly observe the soft mode (SM) associated with the Curie-Weiss behavior of the dielectric constant $\varepsilon $(T). The results are treated within the framework of the coupled SM and transverse optic (TO1) mode and the temperature dependence of the SM frequency at q=0.075 a* is determined. The parameters of the SM are consistent with the earlier estimates and the frequency exhibits a minimum near the Burns temperature ($\approx $ 650K)