An innovative approach of structural instabilities in tetragonal tungsten bronze crystals through the concept of rigid unit modes

TL;DR

This paper explores the rigid unit modes in tetragonal tungsten bronze crystals, linking theoretical predictions with experimental data to understand structural instabilities and potential phase transformations.

Contribution

It provides a comprehensive analysis of RUMs in TTB structures and predicts possible crystal structures resulting from mode condensation.

Findings

Identification of all RUMs in ideal TTB lattice

Correlation between RUMs and ferroelastic transformations

Experimental data supports theoretical predictions

Abstract

Tetragonal tungsten bronze (TTB) oxides are one of the most important classes of ferroelectrics. Many of these framework structures undergo ferroelastic transformations related to octahedron tilting deformations. Such tilting deformations are closely related to the Rigid Unit Modes (RUMs). This paper discusses the whole set of RUMs in an ideal TTB lattice and possible crystal structures which can emerge owing to the condensation of some of them. Analysis of available experimental data for the TTB-like niobates lends credence to the obtained theoretical predictions.