npj:二维五边形结构:极化材料设计的新架构
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来自北京交通大学物理系的郭亚光副教授与西安交大周健教授和北京大学王前教授合作,将五边形密铺平面的数学模型引入极化材料的设计,提出了二维五边形结构 “不等价三配位原子”的设计方案,并由此开发了一种基于对称性比较的高通量结构搜索方法,在Materials Project数据库中筛选出8种稳定的具有面内永久极化的二维五边形过渡金属化合物。这些材料在1500 K时仍可保持良好的热稳定性,从而规避了高温下铁电极化消失的问题。
通过第一性原理计算,该工作还系统研究了这些单层极性材料在机电转换和光电转换方面的性质,结果表明:
1) 相比于单质和二元五边形材料,三元结构面内的中心对称性被打破,使得正负电荷在空间上的分离不受二维材料厚度的限制,进而应力诱导的压电响应提高了3个数量级;
2) 三元五边形结构具有优异体光伏效应 (bulk photovoltaic effect),其位移电流 (shift current) 在可见光区域最高可达300 μAV-2,这源于体系非点式对称操作(二重螺旋轴)诱导能带在X→M路径上发生二重简并,从而提升了带间跃迁的效率。该工作不仅有效增加了热释电材料的种类,同时在能量转换领域也拓展了二维五边形材料的应用范围。
该文近期发表于npj Computational Materials 8: 40 (2022),英文标题与摘要如下,点击左下角“阅读原文”可以自由获取论文PDF。
Screening transition metal-based polar pentagonal monolayers with large piezoelectricity and shift current
Yaguang Guo, Jian Zhou, Huanhuan Xie, Yanyan Chen, & Qian Wang*
Two-dimensional (2D) materials entirely composed of pentagon motifs are of interest for their wide applications. Here, we demonstrate that in-plane polar symmetry can exist in ternary pentagonal monolayers, where the induced electric polarization is not associated with specific conditions, such as ferroelectric phase transition, strain gradient, and layer stacking, but is an intrinsic structural property coming from the orderly arranged polar bonds. Based on our high-throughput screening method and first-principles calculations, we find eight stable 2D polar transition metal compounds with a number of intriguing properties. In particular, their piezoelectric coefficients are three orders of magnitude larger than those of 2D elemental and binary pentagonal structures, and the shift current can reach up to 300 μAV-2, superior to that of 2D conventional ferroelectric materials like GeS. Our identified pentagonal monolayers not only expand the family of 2D pyroelectric materials, but also hold potentials for energy conversions.
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