Local symmetry and polarization in relaxor-based ferroelectric crystals

Kim, Kyou Hyun

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https://hdl.handle.net/2142/45292 Copy

Description

Title

Local symmetry and polarization in relaxor-based ferroelectric crystals

Author(s)

Kim, Kyou Hyun

Issue Date

2013-08-22T16:35:02Z

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

Zuo, Jian-Min

Doctoral Committee Chair(s)

Zuo, Jian-Min

Committee Member(s)

• Payne, David A.
• Dillon, Shen J.
• Martin, Lane W.

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Piezoelectric
• Relaxor-ferroelectric single crystal
• Morphotropic phase boundary
• Symmetry
• Convergent beam electron diffraction
• Nanodomain structure
• Transmission Electron Microscopy (TEM)

Abstract

Relaxor-ferroelectric single crystals, such as (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT), have the potential to transform technologies of medical imaging, actuation, and sensors, due to their extraordinary high piezoelectric effect. It has been suggested that polarization rotation driven by external electric fields is responsible for the large piezoelectric response. Polarization rotation is accompanied by a change in crystal symmetry and/or orientation. However, the nature of symmetry in PMN-xPT and other relaxor-ferroelectric crystals, despite extensive study by x-ray and neutron diffraction, is still controversial. Extensive studies have suggested the crystal symmetry varies on the nanoscopic scale and understanding the nature of local symmetry and its variations is thus critical to correlate the structure with polarization properties. In this thesis, the symmetry is measured based on the size of the crystal volume and the volume position in PMN-xPT single crystals. The study is enabled by the use of probes of different length scales to examine the symmetry of PMN-xPT single crystals. Local symmetry recorded by different probes is measured using quantitative convergent beam electron diffraction analysis (CBED) and transmission electron microscopy (TEM). Symmetry in CBED patterns is correlated with polarization direction with help of simulations. Furthermore, local symmetry fluctuation is observed using a new CBED method developed during this research. The technique enables the quantification of local symmetry development.

Graduation Semester

2013-08

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http://hdl.handle.net/2142/45292

Copyright and License Information

Copyright 2013 Kyou Hyun Kim

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