摘要: 外延生长铁电薄膜中基底失配应变能够调控微观铁电畴结构和宏观铁电性能。本文选择了三种相结构（四方相、四方和菱方混合相、菱方相）PbZr(1-x) TixO3 (x=0.8, 0.48, 0.2) 铁电薄膜，利用相场模拟研究了在不同基底失配应变(εsub)作用下，三种成分铁电薄膜中微观畴结构的演化以及宏观极化-电场回线。随着应变从-1.0%变化到1.0%，三种相结构铁电薄膜的矫顽场、饱和极化值和剩余极化值全都降低，其中PbZr(1-x) TixO3 (x=0.48)薄膜的饱和极化值和剩余极化值比另外两种薄膜降低更快。模拟结果表明拉应变能提高铁电薄膜储能效率，其中准同型相界处应变提升储能效率最快。本工作揭示了应变对PbZr(1-x) TixO3铁电薄膜中畴结构、电滞回线以及储能等方面的影响，为铁电功能薄膜材料的实验设计提供了理论基础。
Phase field simulation of misfit strain manipulating domain structure and ferroelectric properties in PbZr(1-x)TixO3 thin films
- Received Date:
28 February 2020
Abstract: Ferroelectric domain structure and ferroelectric properties in the hetero-epitaxially constrained ferroelectric thin films can be manipulated by substrate misfit strain. In this work, three kinds of phase structures of PbZr(1-x)TixO3 thin films, including tetragonal, tetragonal- rhombohedral-mixed and rhombohedral phases, are investigated. Firstly, ferroelectric domain structures at different substrate misfit biaxial strains are obtained by phase-field simulation. Then we calculated the polarization-electric field hysteresis loops at different misfit strains, and obtained the coercive field, saturation polarization, and remnant polarization. In tetragonal PbZr(1-x)TixO3 (x=0.8) thin films, compressive strain contributes to the formation of out-of-plane c1/c2 domain, and tensile strain favors in-plane a1/a2 domain formation. With the increase of compressive strain, tetragonal-rhombohedral phases coexist in PbZr(1-x)TixO3 (x=0.48) films near the morphotropic phase boundary, while tensile strain decreases the rhombohedral domain size. In rhombohedral PbZr(1-x)TixO3 (x=0.2) films, the rhombohedral domains are steady states under compressive and tensile strains. As the misfit strain changes from -1.0% to 1.0%, the value of the coercive field, saturation polarization and remnant polarization decrease. Among them, for tetragonal-rhombohedral mixed phase, the reductions of saturation field and remnant polarization are larger than tetragonal and rhombohedral phases. The coercive field of mixed phase decreases rapidly under compressive strain, while deceases slowly under tensile strain. It is worth noting that the remnant polarization decrease faster than saturation polarization in three components of ferroelectric thin films. Due to the electromechanical coupling, when x=0.48 at the morphotropic phase boundary shows that the remnant polarization reduction is faster than that of the other two types ferroelectric thin films, and the small coercive field are obtained in large tensile strain. Therefore, tensile strain can effectively improve the energy storage efficiency in ferroelectric thin films, and the efficiency of x=0.48 thin film increases significantly comparing with x=0.8 or 0.2. Both the ratio of rhombohedral/tetragonal phase and the domain size will play a significant role on ferroelectric performance. Therefore, our results contribute to understand the electromechanical coupling mechanism of PbZr(1-x)TixO3, and provide guidance for the experimental design of ferroelectric functional thin film materials.