Role of point defects in Perovskite microwave resonators

Letourneau, Steven

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https://hdl.handle.net/2142/49472 Copy

Description

Title

Role of point defects in Perovskite microwave resonators

Author(s)

Letourneau, Steven

Issue Date

2014-05-30T16:45:58Z

Director of Research (if dissertation) or Advisor (if thesis)

Kriven, Waltraud M.

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• perovskite
• neutron diffraction
• defects
• vacancies

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.

Graduation Semester

2014-05

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http://hdl.handle.net/2142/49472

Copyright and License Information

Copyright 2014 Steven Letourneau

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