Abstract The assignment of the optical phonons to the specific active modes of an arbitrary crystal structure provides important keys to establish a proper correlation between the structural changes, microstructural characterization and the properties of the material. A short-range force-field model is, therefore, applied to investigate the optical phonon distributions and complex behavior of atomic motions in distorted orthorhombic (space group: Pbnm) perovskites RCrO3 (R = La, Pr, Nd, Sm, Eu). The lattice dynamics calculations are performed taking account of the nine bond-stretching and seven angle-bending force constants within the framework of normal coordinate analysis. The model calculations provide good agreement between our theoretical and the previously observed Raman and infrared modes of orthochromites RCrO3. All of the total forty nine optical modes of these perovskites are assigned to the specific modes at Γ-point of the Brillouin zone simultaneously. The potential energy distribution (PED) coefficients have also been evaluated to investigate the contribution of each force constant to the calculated optical phonon modes. Depending on the bond strengths and PED of various coupling between ions forming bonds, complex behavior of several low-wave number Raman modes, namely, mode mixing and mode crossing, in the light of atomic movements are addressed for this series of orthochromites.

中文翻译：

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使用力场晶格动力学模型在畸变正交 RCrO3（R = La、Pr、Nd、Sm、Eu）钙钛矿区中心分配光学声子

摘要 将光学声子分配给任意晶体结构的特定活性模式，为在结构变化、微观结构表征和材料性质之间建立适当的相关性提供了重要的关键。因此，应用短程力场模型来研究畸变正交（空间群：Pbnm）钙钛矿 RCrO3（R = La、Pr、Nd、Sm、Eu）中原子运动的光学声子分布和复杂行为。晶格动力学计算是在法线坐标分析框架内考虑九个键拉伸和七个角度弯曲力常数进行的。模型计算在我们的理论和之前观察到的正铬铁矿 RCrO3 的拉曼和红外模式之间提供了很好的一致性。这些钙钛矿的全部 49 个光学模式同时分配给布里渊区 Γ 点的特定模式。还评估了势能分布 (PED) 系数，以研究每个力常数对计算出的光学声子模式的贡献。根据形成键的离子之间各种耦合的键强度和 PED，针对这一系列的正铬铁矿，根据原子运动解决了几种低波数拉曼模式的复杂行为，即模式混合和模式交叉。还评估了势能分布 (PED) 系数，以研究每个力常数对计算出的光学声子模式的贡献。根据形成键的离子之间各种耦合的键强度和 PED，针对这一系列的正铬铁矿，根据原子运动解决了几种低波数拉曼模式的复杂行为，即模式混合和模式交叉。还评估了势能分布 (PED) 系数，以研究每个力常数对计算出的光学声子模式的贡献。根据形成键的离子之间各种耦合的键强度和 PED，针对这一系列的正铬铁矿，根据原子运动解决了几种低波数拉曼模式的复杂行为，即模式混合和模式交叉。