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Title:Role of point defects in Perovskite microwave resonators
Author(s):Letourneau, Steven
Advisor(s):Kriven, Waltraud M.
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
neutron diffraction
Abstract:Perovskite ceramics are used in a plethora of applications, including electroceramics, superconductors, semiconductors, refractories, catalysts, magnetoresistors, proton conductors, and substrates for semiconductor heteroepitaxy. Engineering defective structures in an attempt to modify properties is a long-established technique in materials chemistry; yet, no models exist which can predict the structure of perovskite compounds containing extrinsic point defects such as vacancies. An empirical approach is used here to develop a predictive model based solely on chemical composition and published ionic radii. Effective vacancy sizes were derived both empirically from an existing model for pseudocubic lattice-constants, as well as experimentally, from average bond lengths calculated from neutron diffraction data. Compounds of strontium-doped magnesium titanate were synthesized by the inorganic-organic steric-entrapment method with vacancies engineered on both the A- and B-sites. Effective vacancy sizes were then used in empirical models to predict changes in lattice constants. Interestingly, using experimentally refined bond lengths in the derivation of effective vacancy size seemed to overestimate the effect of these point defects. However, the use of calculated vacancy sizes, derived from previously reported prediction models, showed significant improvements in the prediction of the pseudocubic perovskite lattice.
Issue Date:2014-05-30
Rights Information:Copyright 2014 Steven Letourneau
Date Available in IDEALS:2014-05-30
Date Deposited:2014-05

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