退极化场对Ba_(0.5)Sr_(0.5)TiO_(3)外延薄膜的铁电和介电性能的影响

The Effect of Depolarization Field on Ferroelectric and Dielectric Properties of Ba_(0.5)Sr_(0.5)TiO_(3) Epitaxial Thin Films

基于Ginzburg-Landau-Devonshire唯象理论,定性研究了在有或无退极化场情形下外延Ba_(0.5)Sr_(0.5)TiO_(3)薄膜的铁电和介电性能随厚度的依赖特性。结果表明:与无退极化场相比,退极化场的存在使薄膜极化强度空间分布更均匀,抑制了系统的平均极化强度,降低了相变温度(ΔT_(c)),但增加了临界厚度(Δh_(c)、Δh_(m))和调谐率(Δφ),尤其在电极弱补偿情况下更加显著,厚度为100 nm时薄膜的ΔT_(c)、Δh_(c)、Δh_(m)和Δφ分别约为-57.5℃、15 nm、40 nm和20%;外延薄膜的介电性能取决于极化强度对外加电场的响应能力,而非极化本身,这一观点可从完全相反的极化强度和调谐率厚度依赖性趋势充分证明。

Based on the Ginzburg-Landau-Devonshire phenomenological theory,the thickness-dependent ferroelectric and dielectric properties with and without depolarization field in epitaxial Ba_(0.5)Sr_(0.5)TiO_(3) films were qualitatively studied.The results show that,compared with non-depolarization field,depolarization field makes the spatial distribution of polarization more uniform and inhibits the average polarization of the system,with the phase transition temperature(ΔT_(c))reduced but the critical thickness(Δh_(c),Δh_(m)),and tunability(Δφ)increased,especially in the case of weak electrode compensation.With the 100-nm-thickness thin film,the values ofΔT_(c)、Δh_(c)、Δh_(m) andΔφare about-57.5℃,15 nm,40 nm and 20%,respectively.Moreover,the dielectric properties of epitaxial films depend on the ability of polarization to respond to external applied electric field rather than polarization itself,which can be fully proved by the completely opposite trends of thickness-dependent polarization and tunability.