应变诱导外延Ba0.6Sr0.4TiO3薄膜铁电介电性能的频率依赖特性

基于修正的Landau-Devonshire唯象理论和Landau-Khalatnikov方程，研究了不同失配应变下外延Ba_0.6Sr_0.4TiO₃薄膜相稳定性和频率依赖的铁电介电性能。结果表明:室温下铁电c相、正交aa相和顺电相为稳态相且均为二级相变；在0.1 kHz的外加电场频率下，压应变增加了c相的面外剩余极化强度(P_r)和矫顽场(E_c)，而拉应变增加了aa相的面内剩余极化强度和矫顽场。此外，随着频率的增加，相界处P_r和E_c均增加，介电常数呈先快速后缓慢的下降趋势，最大调谐率逐渐减小且相应失配应变逐渐趋于零，这主要归因于频率的增加导致相变温度(ΔT_c)升高。进一步计算显示，面外的失配应变移动、调谐率降低和ΔT_c分别为0.017%、10.6%、7.3 ℃，其与面内结果(0.019%，9.7%，7.7 ℃)相近。

The Frequency-dependent Ferroelectric and Dielectric Properties of Strain-induced Epitaxial Ba0.6Sr0.4TiO3 Thin Films

Phase stability and frequency-dependent ferroelectric and dielectric properties of epitaxial Ba_0.6Sr_0.4TiO₃ thin films under different misfit strains were investigated using a modified Landau-Devonshire phenomenological theory combined with Landau-Khalatnikov equation. The phase diagram analysis indicates that ferroelectric tetragonal (c), orthogonal (aa) and paraelectric phases are stable at room temperature and all phase transitions are of second order. The compressive misfit strain increases out-of-plane remnant polarization (P_r) and coercive field (E_c) in c phase while the tensile misfit strain augments in-plane P_r and E_c in aa phase at an electric field frequency of 0.1 kHz. Moreover, it is found that both polarization and coercive field increase with increasing frequency while the dielectric constant decreases rapidly first and then slowly. The maximum tunability decreases and the corresponding misfit strain gradually approaches zero, which is attributed to the enhancement of phase transition temperature (ΔT_c). The further calculation results reveal that the shift of misfit strain, decrease in tunability and ΔT_c are 0.017%, 10.6% and 7.3 ℃ respectively in the out-of-plane case, which are comparable to 0.019%, 9.7% and 7.7 ℃ respectively for the in-plane case.