Expanding an Empirical Models of Perovskites
Faculty Mentor Information
Rick Ubic
Presentation Date
7-2017
Abstract
Perovskites are ubiquitous in modern devices because their wide compositional range and structural variability gives rise to useful properties like piezoelectricity, pyroelectricity, ferroelectricity, superconductivity, colossal magnetoresistance, proton conduction, catalysis, and spin-dependent transport. While a few theoretical models exist for some perovskite structures, few are suited to the doped ceramics used in commercial devices. An entirely new empirical modelling technique, which can easily accommodate these phenomena, was recently developed; and this work expands the validity limits of that model. Specifically, the goal is to extend the model to accommodate perovskites containing cuboctahedrally-coordinated cations which are smaller than 1.34 Å (Ca2+). Toward that end, some of the Ca2+ in Ca1-3xLa2xTiO3 has been replaced with Mg2+ (~1.2 Å). Lattice constants were determined via Rietveld refinements of x-ray diffraction data, and from them the effective sizes of both ions and vacancies, as well as effective tolerance factors, were calculated. A new model for the effective tolerance factor – a key structural indicator – has been proposed.
Expanding an Empirical Models of Perovskites
Perovskites are ubiquitous in modern devices because their wide compositional range and structural variability gives rise to useful properties like piezoelectricity, pyroelectricity, ferroelectricity, superconductivity, colossal magnetoresistance, proton conduction, catalysis, and spin-dependent transport. While a few theoretical models exist for some perovskite structures, few are suited to the doped ceramics used in commercial devices. An entirely new empirical modelling technique, which can easily accommodate these phenomena, was recently developed; and this work expands the validity limits of that model. Specifically, the goal is to extend the model to accommodate perovskites containing cuboctahedrally-coordinated cations which are smaller than 1.34 Å (Ca2+). Toward that end, some of the Ca2+ in Ca1-3xLa2xTiO3 has been replaced with Mg2+ (~1.2 Å). Lattice constants were determined via Rietveld refinements of x-ray diffraction data, and from them the effective sizes of both ions and vacancies, as well as effective tolerance factors, were calculated. A new model for the effective tolerance factor – a key structural indicator – has been proposed.