Electromechanical phenomena in non-centrosymmetric materials subject to strain gradients = 반전대칭이 깨진 물질에서 변형구배에 의한 전기기계 현상

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The flexoelectric effect is a ubiquitous electromechanical phenomenon arising in any dielectric material. Despite of its ubiquitousness, it is relatively insignificant in the macroscopic scale because applying a large strain gradient without fracturing or cracking is a hard task. In nanoscale systems, however, huge gradients as much as $10^5$ ~ $10^7 m^{-1}$ are often present, and the flexoelectric effect becomes one of the major electromechanical couplings. In this work, the photocurrent enhancement at the interfaces bearing large strain gradients due to the flexoelectric effect is addressed. The morphotropic phase boundary of the bismuth ferrite thin film system is used as the model system. The vector piezoresponse force microscopy technique is developed to visualize the complex domain structures in the vicinity of the phase interfaces. The interfaces under large strain gradients show the dipolar feature implying the presence of the depolarization field originated by the flexoelectric effect. Based on the experimental observations and the phase field simulation, the non-linear flexoelectric effect arising at the non-centrosymmetric system is proposed. To deepen the understanding of the flexoelectricity, the ionic chain network model reproducing the flexoelectric effect is introduced. The conventional linear flexoelectric effect and the quadratic flexoelectric effect are manipulated by tuning the model parameters. In the model system, the difference in the interaction strengths among the same kind ions is responsible for the linear flexoelectric effect. Also the broken inversion symmetry generates the quadratic flexoelectric effect, and the marginal strain gradient that the linear and quadratic flexoelectric effects give the same magnitude of polarization is estimated.
Advisors
Yang, Chan-Horesearcher양찬호researcher
Description
한국과학기술원 :물리학과,
Publisher
한국과학기술원
Issue Date
2017
Identifier
325007
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 물리학과, 2017.2,[v, 101 p. :]

Keywords

Strain gradient▼aFlexoelectric▼anon-centrosymmetric▼avector Piezoresponse Force Microscopy▼aBismuth ferrite; 변형구배▼a플렉소전기▼a비반전대칭▼a벡터압전감응힘현미경▼a비스무트 페라이트

URI
http://hdl.handle.net/10203/264661
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=866908&flag=dissertation
Appears in Collection
PH-Theses_Ph.D.(박사논문)
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