Microscopic mechanisms behind hyperferroelectricity

M. Khedidji, D. Amoroso, H. Djani
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引用次数: 2

Abstract

Hyperferroelectrics are receiving a growing interest thanks to their unique property to retain a spontaneous polarization even in presence of a depolarizing field. Nevertheless, general microscopic mechanisms driving hyperferroelectricity, which is ascribed to the softening of a polar $LO$ mode, are still missing. Here, by means of phonons calculations and force constants analysis in two class of hyperferroelectrics, the ABO$_3$-LiNbO3-type systems and the prototypical hexagonal-ABC systems, we unveiled common features in the dynamical properties of a hyperferroelectric behind such $LO$ instability: negative or vanishing on-site force constant associated to the cation driving the $LO$ polar distortion, and destabilizing cation-anion interactions, both induced by short-range forces. We also predict possible enhancement of the hyperferroelectric properties by applying an external positive pressure; pressure strengthens the destabilizing short-range interactions. Particularly, the increase in the mode effective charges associated to the unstable $LO$ mode under pressure suggests an eventual enhancement of the $D$=0 polarization under compressive strain.
超铁电性背后的微观机制
超铁电体由于其独特的性质,即使在去极化场的存在下也能保持自发极化,因此受到越来越多的关注。然而,驱动超铁电性的一般微观机制(归因于极性$LO$模式的软化)仍然缺失。本文通过对两类超铁电体(ABO$_3$- linbo3型体系和典型六边形- abc体系)的声子计算和力常数分析,揭示了这种超铁电体不稳定性背后的动力学特性的共同特征:与驱动$LO$极性畸变的阳离子相关的负或消失的现场力常数,以及不稳定的阳离子-阴离子相互作用,都是由短程力引起的。我们还预测了施加外部正压可能增强超铁电性能;压力加强了破坏稳定的短程相互作用。特别是,与压力下不稳定的$LO$模式相关的模式有效电荷的增加表明,在压缩应变下,$D$=0极化最终会增强。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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