柴国钟，周　挺，吴化平，张　征，董晨晨

(浙江工业大学 特种装备制造与先进加工技术教育部重点实验室， 浙江 杭州 310014)

挠曲电效应对超薄铁电薄膜物理性能的调控

柴国钟，周挺，吴化平，张征，董晨晨

(浙江工业大学 特种装备制造与先进加工技术教育部重点实验室， 浙江 杭州 310014)

摘要：具有量子隧穿及阻变存储效应的超薄铁电薄膜引起了广泛的关注.在超薄铁电薄膜中，应变及应变梯度效应十分明显，因此由应变梯度所产生的挠曲电效应不可忽视.挠曲电效应是指应变梯度或非均匀应变场能局部地破坏反演对称，从而导致晶体产生电极化的效应.基于朗道热力学理论，建立了考虑挠曲电效应的超薄铁电薄膜相变的理论模型.通过该模型研究了挠曲电效应对纳米尺度超薄BaTiO3薄膜相变温度、铁电性能以及热释电系数的影响.研究结果表明：挠曲电效应提高铁电薄膜的电极化值和临界厚度，降低薄膜的相变温度.利用挠曲电效应可有效调控超薄铁电薄膜的相变温度及热释电系数。

关键词：挠曲电效应；铁电薄膜；热力学理论；应变梯度；热释电系数

The effect of flexoelectricity on the phase transition and physics properties

of ultrathin ferroelectric films

CHAI Guozhong, ZHOU Ting, WU Huaping, ZHANG Zheng, DONG Chenchen

(Key Laboratory of Special Purpose Equipment and Advanced Manufacturing Technology, Ministry of Education,

Zhejiang University of Technology, Hangzhou 310014, China)

Abstract:Recently, ultrathin ferroelectric films with quantum tunneling and resistance change storage effect have attracted widespread attention. Strain and strain gradient in ultrathin ferroelectric films is extremely significant so that the flexoelectricity cannot be ignored. Flexoelectricity describes that strain gradient or inhomogeneous strain breaks the inversion symmetry and induces polarization in crystals. Based on the Landau thermodynamic theory, phase transition model of ultrathin ferroelectric films including flexoelectricity is established. Using this theoretical model, the effect of flexoelectricity on phase transition temperature, ferroelectric properties and pyroelectric coefficients of ultrathin BaTiO3films are studied. The result shows that flexoelectricity increase the polarization and critical thickness while decrease the phase transition temperature in epitaxial BTO films. Thus the phase transition temperature and pyroelectric coefficients of ultrathin ferroelectric films can be effectively adjusted by flexoelectricity。

Keywords:flexoelectricity; ferroelectric films; thermodynamic theory; phase transition; pyroelectric coefficient

挠曲电效应是指应变梯度或非均匀应变场能局部地破坏反演对称，从而导致晶体，甚至中心对称晶体产生电极化[1].Kogan等[2]最早就报道了应变梯度和电场之间的耦合关系.Indenbom等[3]在其基础上，首次提出了“挠曲电”这一物理概念，然而由于块体材料的非局部应变场往往很小，早期的研究中挠曲电……