Linking local structural distortions to global symmetry-breaking in hexagonal BaTiO3

Ferroelectric (FE) ceramics comprise critical components of contemporary electronic devices due to their appealing electromechanical properties. BaTiO3 is one of the most renowned FE materials owing to its complex sequence of phase transitions away from cubic symmetry, which we have recently been shown to be compatible with an order-disorder mechanism rather than the more traditional displacive mechanism invoked previously. However, it is currently unclear how such a mechanism may be compatible with more complex chemical architectures which do not exhibit such high symmetry as the perovskite aristotype. We have recently revisited the crystal structure of the FE six-layer hexagonal (6H) polytype of BaTiO3, which possesses a contrasting structural topology compared to the cubic polytype. Several signatures of local structural distortions have been previously evidenced to occur in this material, though no local structural studies have ever been performed to corroborate these findings. We expect global symmetry-breaking distortions in 6H-BaTiO3 will be anticipated by local structural distortions as our recent insight into the cubic polytype has demonstrated, so we seek to perform a bespoke total scattering experiment on Polaris to study the transferability of the order-disorder model of ferroelectricity to 6H-BaTiO3. This will inform how similarly appealing FE functionalities may be realised through local symmetry-breakings across a much broader array of material architectures.