Unusual local dipolar correlations in perovskite-based ferroelectrics

The goal of the 21st century crystallographic studies of materials is not limited to fingerprinting and quantifying phases of different symmetries, but more importantly, to expose, extract and quantify atomistic information to establish generic structure-property relationships of materials. In this context, total scattering method, commonly known as pair distribution function (PDF) analysis, has revolutionized the structural investigations for a wide range of functional materials by providing atomic-level structural correlations in ambient and non-ambient conditions. To this end, we have applied the total scattering method together with Raman spectroscopy to a series of popular ferroelectric solid solutions to understand the much-debated topic of composition-driven structural phase transitions leading to anomalous changes in physical properties with composition. Structural models implementing reverse Monte Carlo technique against the experimental PDFs were refined to depict the composition-induced structural changes in term of magnitudes and directions of the cationic dipolar displacements. Combined with the development of the phonon modes, the results not only revealed hitherto unexpected and unpredicted local structural features that can be related to the physical properties, but also a new approach to conceive the structure-property connections for complex ferroelectric systems.