Local atomic order and hierarchical polar nanoregions in a classical relaxor ferroelectric.

The development of useful structure-function relationships for materials that exhibit correlated nanoscale disorder requires adequately large atomistic models which today are obtained mainly via theoretical simulations. Here, we exploit our recent advances in structure-refinement methodology to demonstrate how such models can be derived directly from simultaneous fitting of 3D diffuse- and total-scattering data, and we use this approach to elucidate the complex nanoscale atomic correlations in the classical relaxor ferroelectric PbMgNbO (PMN). Our results uncover details of ordering of Mg and Nb and reveal a hierarchical structure of polar nanoregions associated with the Pb and Nb displacements.

Coupling of emergent octahedral rotations to polarization in (K,Na)NbO ferroelectrics.

Perovskite potassium sodium niobates, KNaNbO, are promising lead-free piezoelectrics. Their dielectric and piezoelectric characteristics peak near x = 0.5, but the reasons for such property enhancement remain unclear.

Reverse Monte Carlo refinements of local displacive order in perovskites: AgNbO3 case study.

Reverse Monte Carlo refinements with combined input from neutron/x-ray total scattering and extended x-ray absorption fine structure (EXAFS) were applied to analyze local atomic displacements in perovskite-related AgNbO(3). This compound exhibits complex displacive order-disorder behavior that determines the unique dielectric properties of AgNbO(3)-based ceramics. Our results revealed that the total scattering and EXAFS data collected from polycrystalline samples were insufficient to reproduce the correlated local Nb displacements which are evident from the diffuse scattering observed in electron diffraction.