Date of Degree

9-2017

Document Type

Dissertation

Degree Name

Ph.D.

Program

Physics

Advisor(s)

Yuhang Ren

Committee Members

Steve Greenbaum

Ying-Chih Chen

Jun Ouyang

Yu Zhang

Subject Categories

Ceramic Materials | Optics | Physics

Keywords

Second Harmonic Generation, Defect Chemistry, Dielectric, Ferroelectric, Perovskite, Crystal Structure

Abstract

In order to improve future generations of dielectric capacitors a deeper understanding of voltage-induced dielectric breakdown and electrical energy storage limitations is required. This dissertation presents the use of far-field optical second harmonic generation (SHG) polarimetry for probing structural defects and polar domains in linear and nonlinear perovskite dielectric ceramics. We investigated the formation of electric field-induced structural distortions at pristine Fe-doped SrTiO3 (Fe:STO) electrode interfaces, structural defect and strain formation due to oxygen vacancy migration in electrodegraded Fe:STO single crystals, and mixed tetragonal and rhombohedral phase domains in ferroelectric Zr-doped BaTiO3 (BZT) films exhibiting excellent energy storage performances. Local oxygen vacancy concentration and diffusion are demonstrated to influence field-induced electrostriction effects. We further show that long-range oxygen vacancy migration results in strain formation across electrocoloration boundaries and structural inhomogeneity at electrodegraded metal-dielectric interfaces. Furthermore, our study of substrate and thickness effects on coexisting tetragonal and rhombohedral phases in ferroelectric BZT films provides significant insights into the strain engineering of heterophase polydomain structures for high energy performance. We show how the formation of second-order rhombohedral nanodomains leads to considerable P-E hysteresis reduction resulting in increased recyclable energy densities and decreased energy losses during charge-discharge cycles.

 
 

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