发表机构
Chalmers University of Technology; University of Birmingham（查尔姆斯理工大学; 伯明翰大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过机器学习势模拟发现，混合卤化物钙钛矿中的卤素有序性显著影响结构相变温度，是决定其相稳定性的关键因素。
AI 中文摘要
混合卤化物钙钛矿是高度多功能的半导体，在光伏、发光二极管和光电探测器等领域具有应用前景。理解其热力学相行为对于指导组分设计和提高器件稳定性至关重要。在此，我们基于密度泛函理论参考数据，为CsxRb1-xPbBr3yI3-3y、CsxRb1-xPbBr3yCl3-3y和CsxRb1-xPbCl3yI3-3y卤化物钙钛矿训练了机器学习原子间势（MLIPs），从而能够进行大规模混合蒙特卡罗-分子动力学模拟，同时采样构型和振动自由度。所有三种二元卤化物体系均表现出混溶间隙，其范围与卤化物离子尺寸失配相关。Br-Cl和Br-I的间隙在低温下闭合，而Cl-I的间隙则延伸至室温以上。在高于混溶间隙的温度（200 K至500 K）下，所有体系均表现出层状卤化物有序化的趋势，卤化物物种优先占据八面体的顶点或赤道位点。在CsPbBr3yI3-3y中，这种有序化发生在与器件相关的温度区间，并与结构相变相关联，使相变温度相对于随机混合结构移动高达100 K。我们将实验观察到的正交-四方相边界强烈的非线性组分依赖性（先线性下降后出现平台）归因于卤化物有序化。在A位引入Rb会削弱卤化物有序化并消除非线性行为，同时缩小Br-I和Br-Cl体系的混溶间隙。这些结果确立了卤化物有序性是混合卤化物钙钛矿结构相稳定性的关键决定因素。
英文摘要
Mixed halide perovskites are highly versatile semiconductors with applications in photovoltaics, light-emitting diodes, and photodetectors. Understanding their thermodynamic phase behavior is central to guiding compositional design and improving device stability. Here, we train machine-learned interatomic potentials (MLIPs) on density functional theory reference data for CsxRb1-xPbBr3yI3-3y, CsxRb1-xPbBr3yCl3-3y, and CsxRb1-xPbCl3yI3-3y halide perovskites, enabling large-scale hybrid Monte Carlo-molecular dynamics simulations that sample both configurational and vibrational degrees of freedom. All three binary halide systems exhibit a miscibility gap, the extent of which correlates with halide ion size mismatch. The gaps in Br-Cl and Br-I close at low temperatures, while the Cl-I gap extends above room temperature. At temperatures above the miscibility gap (200 K to 500 K), all systems show a tendency toward layered halide ordering, with halide species preferentially occupying apical or equatorial octahedral sites. In CsPbBr3yI3-3y, this ordering occurs in a device-relevant temperature regime and is linked to the structural phase transitions, shifting transition temperatures by up to 100 K relative to randomly mixed structures. We attribute the strongly non-linear composition dependence of the orthorhombic-tetragonal phase boundary observed experimentally (a linear decrease followed by a plateau) to halide ordering. Introducing Rb on the A-site weakens halide ordering and eliminates the non-linear behavior, while narrowing the miscibility gap in both the Br-I and Br-Cl systems. These results establish halide ordering as a key determinant of structural phase stability in mixed-halide perovskites.
