鈣鈦礦化合物（通式為ABX3）是一類功能豐富的材料，在催化、電子裝置、感測器和能量儲存等領域具有廣泛應用。通常，鈣鈦礦的性質對微小的結構變化十分敏感，例如：金屬陰離子八面體的旋轉、變形和傾斜。在氧硫化鈣鈦礦中（或更廣泛地在異質陰離子鈣鈦礦中），B-位八面體配位受兩個或多個陰離子控制。原則上，給定金屬離子周圍的不同陰離子構型可能導致不同級別的晶體場強度、鍵合特性和區域性極化，進而決定了基態的結構和功能。儘管混合陰離子鈣鈦礦具有豐富的潛在結構-性質關係，但是，對混合硫族化物鈣鈦礦中陰離子順序的研究仍然很少。
來自美國洛斯阿拉莫斯國家實驗室的Pilania博士及其合作者，利用第一性原理研究了AB(O0.5S0.5)3鈣鈦礦中A = Ca、Sr、Ba和B = Ti、Zr、Hf的陰離子有序。他們首先分析了20個原子構成的AB(O0.5S0.5)3超胞中所有246個獨特對稱性構型，並提煉出控制其相對能量和帶隙變化的各種因素。證明了陰離子排序始終是圍繞HfO3S3八面體的陰離子全順式排列。這種有序趨勢的起源可追溯到電子、彈性和靜電作用的綜合穩定效應。這些定性概念也可以使用最新的機器學習模型進行量化。他們進一步研究了所確定的有序排列的相對穩定性，該相對穩定性是A和B位點化學的函式。他們還探測了材料的電子結構和功能性依賴於化學反應的趨勢。值得指出的是，他們發現確定的基態陰離子有序打破了反演對稱性，從而建立了一個宏觀極化大於30 μC/cm2的氧硫化物鐵電體家族，對電子材料應用具有重要的前景。
該文近期發表於npj Computational Materials 6: 71 (2020)，英文標題與摘要如下，點選https://www.nature.com/articles/s41524-020-0338-1可以自由獲取論文PDF。
Anion order in oxysulfide perovskites: origins and implications
Ghanshyam Pilania, Ayana Ghosh, Steven T. Hartman, Rohan Mishra, Christopher R. Stanek & Blas P. Uberuaga
Heteroanionic oxysulfide perovskite compounds represent an emerging class of new materials allowing for a wide range of tunability in the electronic structure that could lead to a diverse spectrum of novel and improved functionalities. Unlike cation ordered double perovskites—where the origins and design rules of various experimentally observed cation orderings are well known and understood—anion ordering in heteroanionic perovskites remains a largely uncharted territory. In this contribution, we present and discuss insights that have emerged from our first-principles-based electronic structure analysis of a prototypical anion-ordered SrHf(O0.5S0.5)3 oxysulfide chemistry, studied in all possible anion configurations allowed within a finite size supercell. We demonstrate that the preferred anion ordering is always an all-cis arrangement of anions around an HfO3S3 octahedron. As a general finding beyond the specific chemistry, the origins of this ordering tendency are traced back to a combined stabilization effect stemming from electronic, elastic, and electrostatic contributions. These qualitative notions are also quantified using state-of-the-art machine learning models. We further study the relative stability of the identified ordering as a function of A (Ca, Sr, Ba) and B (Ti, Zr, Hf) site chemistries and probe chemistry-dependent trends in the electronic structure and functionality of the material. Most remarkably, we find that the identified ground-state anion ordering breaks the inversion symmetry to create a family of oxysulfide ferroelectrics with a macroscopic polarization >30 μC/cm2, exhibiting a significant promise for electronic materials applications.
【來源：知社學術圈】
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