AI 中文总结
本研究通过DFT计算揭示，甲脒铅卤化物钙钛矿的对称性降低对力学与振动性能的影响随卤化物种类变化，为高机械稳定性光电材料设计提供了微观依据。
AI 中文摘要
基于甲脒的混合卤化物钙钛矿（FAPbX₃，X为Cl、Br、I）因具备优异的光学与电子性能，在光电应用领域已受到广泛关注。然而，晶体对称性降低对其力学行为与稳定性的影响尚未得到全面理解。本研究采用密度泛函理论（DFT）计算，探究了FAPbX₃的立方相与准立方相的结构、弹性、动力学及非线性力学性能；评估了弹性常数、体积模量、剪切模量、杨氏模量、泊松比、声速与德拜温度，并将其与拉伸及压缩载荷下的第二皮奥拉-基尔霍夫应力-应变响应相关联。结果表明，对称性降低的影响强烈依赖于卤化物组分：对于FAPbCl₃与FAPbBr₃，从立方相到准立方相的转变会降低晶格刚度、减小声学声子速度并降低德拜温度；而FAPbI₃则呈现相反趋势。应力-应变分析进一步揭示了显著的非线性、各向异性与非对称力学行为，表明对称性降低可根据卤化物种类激活或抑制应变适配机制，从而调控力学稳定性与结构软化的起始过程。这些发现为甲脒基卤化物钙钛矿中晶体对称性、晶格动力学与非线性力学响应之间的关系提供了微观视角，为机械鲁棒型光电材料的设计提供了有益指导。
英文摘要
Formamidinium-based hybrid halide perovskites (FAPbX3, X = Cl, Br, and I) have attracted considerable attention for optoelectronic applications owing to their outstanding optical and electronic properties. However, the influence of crystal symmetry reduction on their mechanical behavior and stability has not yet been comprehensively understood. In this work, density functional theory (DFT) calculations were performed to investigate the structural, elastic, dynamical, and nonlinear mechanical properties of the cubic and ps-cubic phases of FAPbX3. The elastic constants, bulk, shear, and Young's moduli, Poisson's ratio, sound velocities, and Debye temperature were evaluated and correlated with the second Piola-Kirchhoff stress-strain response under tensile and compressive loading. The results reveal that the effect of symmetry reduction is strongly dependent on the halide composition. For FAPbCl3 and FAPbBr3, the transition from the cubic to the ps-cubic phase reduces the lattice stiffness, decreases the acoustic phonon velocities, and lowers the Debye temperature, whereas the opposite trend is observed for FAPbI3. The stress-strain analysis further reveals pronounced nonlinear, anisotropic, and asymmetric mechanical behavior, demonstrating that symmetry reduction can either activate or suppress strain-accommodation mechanisms depending on the halide species, thereby governing the mechanical stability and the onset of structural softening. These findings provide microscopic insight into the relationship between crystal symmetry, lattice dynamics, and nonlinear mechanical response in formamidinium-based halide perovskites, offering useful guidance for the design of mechanically robust optoelectronic materials.
