Neutron scattering study of PbMg$_{1/3}$Ta$_{2/3}$O$_3$ and BaMg$_{1/3}$Ta$_{2/3}$O$_3$ complex perovskites

TL;DR

This neutron scattering study investigates the structural properties of two complex perovskites, revealing no phase transitions but identifying anomalies and lead displacements in PbMg$_{1/3}$Ta$_{2/3}$O$_3$ related to relaxor behavior.

Contribution

The paper provides detailed neutron scattering analysis showing persistent lead displacements and diffuse scattering in PbMg$_{1/3}$Ta$_{2/3}$O$_3$, linking structural anomalies to relaxor ferroelectric properties.

Findings

PbMg$_{1/3}$Ta$_{2/3}$O$_3$ exhibits anomalies in lattice parameter related to dielectric peaks.

Lead ions are displaced at all temperatures, indicating short-range order.

Diffuse scattering correlates with lead displacements and relaxor behavior.

Abstract

Neutron scattering investigations were carried out in PbMg$_{1/3}$Ta$_{2/3}$O$_3$ and BaMg$_{1/3}$Ta$_{2/3}$O$_3$ complex perovskites. The crystal structure of both compounds does not show any phase transition in the temperature range 1.5 -- 730 K. Whereas the temperature dependence of the lattice parameter of BaMg$_{1/3}$Ta$_{2/3}$O$_3$ follows the classical expectations, the lattice parameter of relaxor ferroelectric PbMg$_{1/3}$Ta$_{2/3}$O$_3$ exhibits anomalies. One of these anomalies is observed in the same temperature range as the peak in the dielectric susceptibility. We find that in PbMg$_{1/3}$Ta$_{2/3}$O$_3$, lead ions are displaced from the ideal positions in the perovskite structure at all temperatures. Consequently short-range order is present. This induces strong diffuse scattering with an anisotropic shape in wavevector space. The temperature dependences of the diffuse neutron scattering intensity and of the amplitude of the lead displacements are similar.