Pressure-induced structural transformations in (1-x)Na0.5Bi0.5TiO3-xBaTiO3 at the morphotropic phase boundary

Pressure-induced structural transformations up to 8.9 GPa in the perovskite-type (ABO3) (1-x)Na0.5Bi0.5TiO3-xBaTiO3 (NBT-xBT) at the morphotropic phase boundary (MPB), xMPB = 0.048, were studied by means of polarized Raman spectroscopy and single-crystal x-ray diffraction. Raman spectroscopic analysis was also performed on reference undoped NBT to reveal the effect of chemical composition on the response of the atomic dynamics to isotropic elastic stress. Our results demonstrate that, like Pb-based relaxors and pure NBT, NBT-0.048BT undergoes multistep structural alteration to a high-pressure state consisting of reduced off-centered displacements of B-site cations, enhanced antipolar order of off-centered shifts of A-site cations, and induced BO6 tilt order. The comparison between NBT and NBT-0.048BT reveals that Ba doping at the level of the MPB composition smears out the pressure range of ongoing structural transformations, slows down the suppression of off-centering for both A- and B-site cations, and hardens the A-cation subsystem but softens the B-cation subsystem. The larger volume compressibility of NBT-0.048BT with respect to NBT suggests that the softening of the B-cation subsystem due to the substitution of Ba controls the bulk compressibility at the MBP.

Automated summary

This study investigated the effect of Ba doping on the structural transformations and properties of perovskite-type composite materials at the morphotropic phase boundary. The results showed that Ba doping reduces the pressure range of structural transformations and slows down the suppression of off-centering for both A- and B-site cations, indicating that Ba doping affects the elasticity and stability of the material.