单畴外延铁电薄膜的相结构与稳定性

PHASE STABILITY OF SINGLE DOMAIN EPITAXIAL FERROELECTRIC FILMS

论文采用动态金茨堡-朗道(DGL)方程研究了薄膜厚度与错配应变对(0 0 1)取向单畴外延PbTiO3(PTO)铁电薄膜相结构与稳定性的影响.结合平面内松弛应变(等效应变)、表面效应与退极化场等机电耦合边界条件,通过数值求解DGL方程获得外延单畴铁电薄膜错配应变-厚度相图和错配应变-温度相图.数值分析结果显示,由于生成的界面位错松弛了薄膜内错配应变,在理论高应变区相图与传统分析结果有较大差别,文中发现在更广的理论错配拉应变区出现稳定的四方相(c相)结构和单斜相(r相)结构.结果也显示,随着薄膜厚度的减小,表面效应与退极化效应会把顺电相扩展到更低温度区域,从而压缩稳定的铁电相存在的温度区域.

The phase stability of single domain ferroelectric PbTiO3 （PTO） epitaxial thin film as a function of the misfit strain and film thickness is studied and discussed systematically using the dynamic Ginzburg-Landau （DGL） equation by taking surface eigenstrain relaxation and depolarization field. Misfit strain film thickness phase diagrams for various temperatures and misfit strain-temperature phase diagrams for various film thicknesses are obtained, respectively. The numerical results show that the phase diagrams in high strain zone are markedly different from previous thermodynamic predictions due to misfit disloca- tions. Especially,we present that there are c-phase and rotational r-phase in a broader misfit tensile strain zone. The results also express that effects of surface and depolarization field obviously shift the paraelectric phase to lower temperature and shrink the ferroelectric phase with decreasing thickness of the films.