Columnar shifts as symmetry-breaking degrees of freedom in molecular perovskites
Columnar shifts as symmetry-breaking degrees of freedom in molecular perovskites
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DOI：
10.1039/c6cp05730f
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发表时间：
2016-01-01
影响因子：
3.3
通讯作者：
Goodwin, Andrew L.
中科院分区：
文献类型：
--
作者：
Bostrom, Hanna L. B.;Hill, Joshua A.;Goodwin, Andrew L.
我们引入柱状位移-集体刚体平移-作为与分子钙钛矿ABX(3) （X =分子阴离子）相行为相关的结构自由度。与传统钙钛矿众所周知的八面体倾斜一样，移位也保留了分子钙钛矿中b位阳离子的八面体配位几何形状，因此易于影响这些局部体系的低能动力学和位移相变。我们对移位激活和晶体对称性破缺之间的相互作用进行了定性概述，并引入了一个通用术语来描述简单的移位畸变，类比于八面体倾斜的“格雷泽符号”。我们将我们的方法应用于解释叠氮化物和甲酸钙钛矿结构的代表性选择，并讨论了在负热膨胀材料和杂化铁电体中位移自由度的功能开发的含义。
We introduce columnar shifts-collective rigid-body translations-as a structural degree of freedom relevant to the phase behaviour of molecular perovskites ABX(3) (X = molecular anion). Like the well-known octahedral tilts of conventional perovskites, shifts also preserve the octahedral coordination geometry of the B-site cation in molecular perovskites, and so are predisposed to influencing the low-energy dynamics and displacive phase transitions of these topical systems. We present a qualitative overview of the interplay between shift activation and crystal symmetry breaking, and introduce a generalised terminology to allow characterisation of simple shift distortions, drawing analogy to the "Glazer notation'' for octahedral tilts. We apply our approach to the interpretation of a representative selection of azide and formate perovskite structures, and discuss the implications for functional exploitation of shift degrees of freedom in negative thermal expansion materials and hybrid ferroelectrics.