Enhanced size-dependent piezoelectricity and elasticity in nanostructures due to the flexoelectric effect
Enhanced size-dependent piezoelectricity and elasticity in nanostructures due to the flexoelectric effect
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DOI：
10.1103/physrevb.77.125424
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发表时间：
2008-03-01
影响因子：
3.7
通讯作者：
Cagin, T.
中科院分区：
文献类型：
--
作者：
Majdoub, M. S.;Sharma, P.;Cagin, T.
晶体压电材料在施加均匀机械应变时发生电致变色。然而，非均匀应变局部破坏反演对称性，甚至可能破坏非压电（中心对称）的对称性。挠曲电性-应变梯度与极化的耦合-由于应变梯度与结构特征尺寸的缩放，预计将显示出强烈的尺寸依赖性。在这项研究中，使用原子和理论的方法相结合，我们调查的“有效”的尺寸依赖的非均匀应变非压电和压电纳米结构的压电和弹性行为。特别是，为了获得分析结果和梳理出物理见解，我们分析了一个典型的纳米悬臂梁。我们发现，在本质上是压电的材料，挠曲电和压电效应不添加线性和表现出非线性的相互作用。后者导致一个强大的尺寸依赖性增强的表观压电系数，导致，例如，一个“巨人”500%的增强，在BaTiO 3的体特性为5 nm的光束厚度。相应地，对于非压电材料，增强也是不平凡的（e。例如，在一个实施例中，在顺电BaTiO 3相中，对于5 nm尺寸为80%）。挠曲电性也改变了纳米结构的表观弹性模量，表现出1/h（2）的渐近缩放，其中h是特征尺寸。我们的主要预测验证了量子力学推导的力场为基础的分子动力学的两个阶段（立方和tetraquartz）的钛酸钡。
Crystalline piezoelectric dielectrics electrically polarize upon application of uniform mechanical strain. Inhomogeneous strain, however, locally breaks inversion symmetry and can potentially polarize even nonpiezoelectric (centrosymmetric) dielectrics. Flexoelectricity-the coupling of strain gradient to polarization-is expected to show a strong size dependency due to the scaling of strain gradients with structural feature size. In this study, using a combination of atomistic and theoretical approaches, we investigate the "effective" size-dependent piezoelectric and elastic behavior of inhomogeneously strained nonpiezoelectric and piezoelectric nanostructures. In particular, to obtain analytical results and tease out physical insights, we analyze a paradigmatic nanoscale cantilever beam. We find that in materials that are intrinsically piezoelectric, the flexoelectricity and piezoelectricity effects do not add linearly and exhibit a nonlinear interaction. The latter leads to a strong size-dependent enhancement of the apparent piezoelectric coefficient resulting in, for example, a "giant" 500% enhancement over bulk properties in BaTiO3 for a beam thickness of 5 nm. Correspondingly, for nonpiezoelectric materials also, the enhancement is nontrivial (e. g., 80% for 5 nm size in paraelectric BaTiO3 phase). Flexoelectricity also modifies the apparent elastic modulus of nanostructures, exhibiting an asymptotic scaling of 1/h(2), where h is the characteristic feature size. Our major predictions are verified by quantum mechanically derived force-field-based molecular dynamics for two phases (cubic and tetragonal) of BaTiO3.