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김상주(Kim Sang-Joo),김주홍(Kim Ju Hong) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
A commercially available PZT wafer that is poled in thickness direction is used to investigate the variations of thermo-electrical material properties of ferroelectric ceramics at high temperatures. The electric displacement in thickness direction and the in-plane strain of the wafer are measured at various high temperatures. From the measurements, the piezoelectric coefficient, permittivity, and pyroelectric coefficient are obtained as functions of temperature and remanent polarization. Finally, the piezoelectric equations giving electric displacement in thickness direction and in-plane strain under a through thickness electric field are proposed.
김상주(Sang-Joo Kim),Stefan Seelecke 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
A three-dimensional model is proposed which can predict the nonlinear behavior of piezoelectric single crystals under electric field or mechanical stress. In the proposed model, six free energy potentials in which six distinct types of tetragonal variants reside are given as quadratic functions of polarization vector and strain tensor. Energy barrier between two energy wells is given as a function of thermodynamic driving force associated with the energy wells. The predictions of the model are compared with recent observations on a ferroelectric single crystal BaTiO₃. The effects of applied stress, 90- and 180-switching processes are discussed in detail.
인장하중을 받을 때 PZT 웨이퍼의 크립 거동 : 실험과 모델링
김상주(Kim Sang-Joo),이창환(Lee Chang-Hoan) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.1
두께방향으로 분극처리되어 있는 상업용 PZT 웨이퍼가 폐쇄회로와 개방회로의 두 가지 전기적 경계조건에서 길이 방향으로 일정한 크기의 인장하중을 받는다. 하중과정 동안 두께 방향으로의 전기밀도와 평면내 변형률의 시간에 따른 변화를 측정한다. 두 가지 전기적 경계조건에서의 서로 다른 거동 특성을 시편 내부에서 발생하는 전기장과 분극역전 현상으로 설명한다. 마지막으로 관측된 크립 거동을 예측하기 위한 정규분포 형식을 가지는 자유에너지 함수를 도입하고 모델의 예측과 실험결과를 비교한다. A commercially available soft PZT wafer that is poled in thickness direction is subjected to longitudinal tensile stress loading in both short and open-circuit conditions. Variations of electric displacement in thickness direction and in-plane strains are measured over time during the loading. Different material responses in the two electrical boundary conditions are explained by the effects of piezoelectrically produced internal electric field on linear material moduli and domain switching mechanisms. Finally, a free energy model of normal distribution is introduced to explain the observed creep behavior, and its predictions are compared with experimental observations.
김상주(Sang-Joo Kim),신준호(Joonho Shin),김윤재(Yun-Jae Kim) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
A two-dimensional finite element model for polarization switching in ferroelectric materials developed by Kim and Jiang<SUP>(1)</SUP> and Sang-Joo Kim<SUP>(2)</SUP> is used to predict the formation of domains in a ferroelectric thin film. Initially the ferroelectric film is poled upward and the bottom electrode is grounded. A strong downward de field is imposed on a point of the top surface of the film. A region of switched domains with downward polarization is nucleated and is grown with time. It is found that initially the shape of the nucleated domains is that of a bulgy dagger, but later it turns into the shape of a reversed cup with the lower part wider than the upper part. It can also be concluded that the size of nucleated domains increases with the period of applied electric potential. The present results are qualitatively consistent with experimental observations.
페로브스카이트 타입 단결정체의 상변태 및 분역스위칭 거동에 대한 모델링
김상주(Sang-Joo Kim) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
A rate-dependent thermo-electro-mechanical free energy model for perovskite type single crystal materials is proposed. The proposed free energy model consists of seven energy wells corresponding to six different types of ferroelectric variants and one paraelectric cubic phase in the ten-dimensional space of electric displacement vector, strain tensor, and temperature. A phase transition or domain switching is described as a jumping process between energy wells, which is governed by thermal activation theory. Various interesting features of the materials under thermo-electro-mechanical environments are calculated and discussed.
김상주(Kim Sang-Joo),이창환(Lee Chang-Hoan) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
A commercially available soft PZT wafer that is poled in thickness direction is subjected to longitudinal tensile stress loading in both short and open-circuit conditions. Variations of electric displacement in thickness direction and in-plane strains are measured over time during the loading. Different material responses in the two electrical boundary conditions are explained by the effects of piezoelectrically produced internal electric field on linear material moduli and domain switching mechanisms. Finally, a free energy model of normal distribution is introduced to explain the observed creep behavior, and its predictions are compared with experimental observations.
김상주(Sang-Joo Kim) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
A ferroelectric(called piezoelectric afterwards) wafer has been widely used as a key component of actuators or sensors of a layer type. According to recent researches, the piezoelectric wafer behaves in a nonlinear way under excessve electro-mechanical loadings. In the present paper, one-dimensional constitutive equation for the nonlinear behavior of a piezoelectrie wafer are proposed based on the prineiples of thermodynamics and a simple viscoplasticity theory, The predictions of the developed model are compared with experimental observations.