## Theses and Dissertations

8-2013

Dissertation

#### Degree Name

Doctor of Philosophy in Physics (PhD)

Physics

Huaxiang Fu

#### Committee Member

Laurent Bellaiche

Gregory Salamo

Michael Lieber

Hameed Naseem

#### Keywords

Pure sciences; Applied sciences; Electron gas; Oxide electronics; Strontium titanate; Titanium; Zirconium

#### Abstract

In this Dissertation we begin with two introductions on: 1) ferroelectricity and related phenomena, and 2) novel properties of Oxide electronics and the generation of two dimensional electron gas. We then give theoretical background of density functional theory (including LDA+U) and pseudopotentials. The first part of research work is about structural, polarization, and dielectric properties of ferroelectric Lead Zirconate Titanate (PZT) solid solution in the form of a nanotube array, embedded in a matrix medium of different ferroelectric strengths. We use the effective Hamiltonian derived from first-principles and finite-temperature Monte Carlo methods to determine the various properties. We revealed different polarization phases of the system in the absence of an external electric field and explained these properties in microscopic detail. In the second part, we study the effects of compressive biaxial inplane strains on the electronic and structural properties of Lanthanum Oxide $\delta$-doped Strontium Titanate supercell. We use first-principles density functional calculations within the local density approximation including also on-site Coulomb interaction energy. We approached the problem by comparing the band structures, localization of electronic states, and cation-anion displacements of unstrained and strained systems. We found a critical strain above which there are abrupt changes in conduction band dispersions and cation-anion displacements, indicating that inplane biaxial strain can drastically tune the properties of this system, which may have potential technological applications.

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