挠曲电效应对超薄铁电薄膜物理性能的调控

The effect of flexoelectricity on the phase transition and physics properties of ultrathin ferroelectric films

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.

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 BaTiO3 films 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.