Total Scattering and the Local Structure of Polar Inorganic Materials

Katharine Page, University of California, Santa Barbara

Polar materials play an important role in science and engineering, and efforts to understand, characterize, design and engineer them is driven by a continued demand for smaller and more robust ferroelectrics as well as a quest for practical multiferroics. As in most functional inorganics, the properties of polar materials are intricately tied to their crystal structures. However, many local atomic configurations - critically important from the viewpoint of technology - are not necessarily described using conventional crystallography. A combination of Rietveld analysis and real-space atomic pair distribution function (PDF) methods for neutron and synchrotron X-ray total scattering data are used to investigate the role local structure plays in the properties of several polar inorganic materials. Examples will include a series of BaTiO3 nanoparticles of different sizes, a family of perovskite oxynitride materials (Ba/Sr/Ca)TaO2N, and Nb-substitution in SrTiO3 (STO) and BaTiO3 (BTO). Total scattering analysis of the nanoparticle data reveals increasing bond distortions with decreasing particle size, contrary to some reports. Local studies in the oxynitride family explore the influence of anion ordering and cation displacements on unusual dielectric properties. In Nb-substituted STO and BTO, subtle yet crucial differences in local structure suggest why the former is metallic while the latter is insulating. The work will demonstrate that combined approaches in reciprocal and real-space often provide unique insight into atomic configurations that influence polar properties.

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