Degree Type

Dissertation

Date of Award

2019

Degree Name

Doctor of Philosophy

Department

Materials Science and Engineering

Major

Materials Science and Engineering

First Advisor

Xiaoli Tan

Abstract

Developing materials with superior functional properties is the primary goal of materials engineering. Nonetheless, the stability of performance during practical service should be of equal importance. This is, with no doubt, also true for piezoelectric materials.

The working conditions of piezoelectric materials can lead to either gradual or abrupt degradation in their functional properties. First, fatigue. In analogy to structural materials under cyclic stresses, the piezoelectric properties deteriorate during the electric field cycling. Second, aging. While the service is paused and the piezoelectric material is sitting idle, the piezoelectric properties will decay over time. Third, thermal depolarization. Electronic devices are not necessarily working at room temperature. The piezoelectric properties may fluctuate with temperature change, or even vanish above a threshold value.

These three major forms of performance instability of piezoelectric materials have been studied for decades. Exploring the microstructural origins can help to find approaches to mitigate the degradation. The current dissertation aims to investigate the micromechanisms of electric fatigue, polarization aging, and thermal depolarization in lead-free piezoelectric ceramics. Electric field in-situ transmission electron microscopy (TEM) is utilized to directly monitor the microstructure evolution during electric cycling, aging, and temperature rise.

Copyright Owner

Zhongming Fan

Language

en

File Format

application/pdf

File Size

123 pages

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