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Polarization canting in ferroelectric diisopropylammonium-halide molecular crystals: a computational first principles study†
Journal of Materials Chemistry C ( IF 6.4 ) Pub Date : 2018-01-19 00:00:00 , DOI: 10.1039/c7tc03732e
Lydie Louis 1, 2, 3, 4 , Krishna Chaitanya Pitike 1, 2, 3, 4 , Ayana Ghosh 1, 2, 3, 4 , Shashi Poddar 4, 5, 6, 7 , Stephen Ducharme 4, 5, 6, 7 , Serge M. Nakhmanson 1, 2, 3, 4, 8
Affiliation  

We report the results of a computational first-principles study of the structural and electrical properties of three ferroelectric diisopropylammonium halides containing chlorine, bromine, and iodine. Calculations were carried out using density-functional theory with maximally-localized Wannier functions utilized for computing electrical polarization within the Modern Theory of Polarization formalism. For each of the crystals, the polar properties for all of the relevant polymorphs were evaluated and decomposed into contributions from individual positive diisopropylammonium and negative halogen-ion charge centers. The calculations show that each diisopropylammonium-halide unit in the crystal possesses a substantial dipole moment with magnitude of 10 to 15 Debye, but that these dipoles are arranged in a mutually opposing manner, leading to full cancellation in the paraelectric phase. In the ferroelectric phase, the dipoles cant along a common polar axis, inducing a small net dipole moment in the crystallographic unit cell, with spontaneous polarization ranging from 5 μC cm−2 for the iodide to 6 μC cm−2 for the bromide and 7 μC cm−2 for the chloride, suggesting no strong dependence of the polarization on the chemical identity of the halide counter ion. We propose that structural modifications of the diisopropylammonium-halide system aimed at stabilization of large unit-dipole cantings could produce molecular crystals with greatly increased spontaneous polarization.

中文翻译:

铁电二异丙基卤化铵分子晶体中的极化倾斜:计算第一性原理研究

我们报告了计算的第一性原理研究的结果,其中包含氯,溴和碘的三种铁电二异丙基卤化铁的结构和电性能。使用密度泛函理论和最大局部的Wannier函数进行计算,该函数用于现代极化理论中的极化计算。对于每种晶体,评估了所有相关多晶型物的极性,并将其分解为单个正二异丙基铵和负卤素离子电荷中心的贡献。计算表明,晶体中的每个二异丙基卤化铵单元都具有一个很大的偶极矩,幅度为10到15德拜,但是这些偶极以彼此相对的方式排列,导致顺电阶段完全消除。在铁电相中,偶极子沿着共同的极轴倾斜,从而在晶体学晶胞中产生小的净偶极矩,自发极化范围为5μCcm-2为碘化物至6μC厘米-2的溴化物和7μC厘米-2的氯化物,表明极化对卤化物抗衡离子的化学特性没有很强的依赖性。我们提出,旨在稳定大的单位偶极子倾斜的二异丙基卤化铵系统的结构修饰可以产生具有大大增加的自发极化的分子晶体。
更新日期:2018-01-19
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