Dynamic Stereochemical Activity of the Sn2+ Lone Pair in Perovskite CsSnBr3
Dynamic Stereochemical Activity of the Sn2+ Lone Pair in Perovskite CsSnBr3
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DOI：
10.1021/jacs.6b06287
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发表时间：
2016-09-14
影响因子：
15
通讯作者：
Seshadri, Ram
中科院分区：
文献类型：
--
作者：
Fabini, Douglas H.;Laurita, Geneva;Seshadri, Ram
S(2)重主族元素上处于较低氧化态的稳定孤对电子驱动了一系列重要的现象，例如在某些铁性材料中出现了极性基态。在这里，我们研究钙钛矿型卤化物CsSnBr3，作为更广泛的材料类的体现。我们发现由于Sn2+S(2)孤子对引起的孤子对立体化学活动导致晶体中隐藏的局域扭曲态在升温时出现，这种现象以前被称为强调。在300~420K温度范围内获得的同步辐射X射线对分布函数揭示了最近邻的锡-溴关联中出现的不对称性，这与动态的Sn2+偏离中心是一致的，尽管没有证据表明偏离平均立方结构。基于密度泛函理论的计算支持了晶格不稳定性的发现：与配位环境中Sn2+的动态偏心有关。光致发光测量表明，随着温度的升高，出现了不寻常的蓝移，这与结构的演变密切相关。在低温下，这些结构反映了八面体旋转的影响。在250K附近，发现了从正交结构(Pnma，编号62)到四方结构(P4/MBM，编号127)的连续转变，并在286K时发生了最终的一级转变为立方结构(Pm(3))，通过巴姆，编号221)。
Stable s(2) lone pair electrons on heavy main-group elements in their lower oxidation states drive a range of important phenomena, such as the emergence of polar ground states in some ferroic materials. Here we study the perovskite halide CsSnBr3 as an embodiment of the broader materials class. We show that lone pair stereochemical activity due to the Sn2+ s(2) lone pair causes a crystallographically hidden; locally distorted state to appear upon warming, a phenomenon previously referred to as emphanisis. The synchrotron X-ray pair distribution function acquired between 300 and 420 K reveals emerging asymmetry in the nearest-neighbor Sn-Br correlations, consistent with dynamic Sn2+ off-centering, despite :there being no evidence of any deviation from the average cubic structure. Computation based on density functional theory supports the finding of a lattice instability associated: with dynamic off-centering of Sn2+ in its coordination environment. Photoluminescence measurements reveal an unusual blue shift with increasing temperature, closely linked to the structural evolution. At low temperatures, the structures reflect the influence of octahedral rotation. A continuous transition from an orthorhombic structure (Pnma, no. 62) to a tetragonal structure (P4/mbm, no. 127) is found around 250 K, with a final, first-order transformation at 286 K to the cubic structure (Pm (3) over barm, no. 221).