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首页> 外文期刊>Physica, B. Condensed Matter >Infrared study of the phonon modes in PrMnO3 and CaMnO3
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Infrared study of the phonon modes in PrMnO3 and CaMnO3

机译：PrMnO3和CaMnO3中声子模的红外研究

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摘要

The infrared (IR) reflectivity spectra of orthorhombic manganese perovskites PrMnO3 and CaMnO3 are studied in the frequency range of optical phonon modes at temperatures varying from 300 to 4 K. The IR phonon spectra of these two materials are analyzed by a fitting procedure based on a Lorentz model, and assigned to definite vibrational modes of Pnma structures by comparison with the results of lattice dynamical calculations. The calculations have been performed in the framework of a shell model using short range Born-Mayer-Buckingham and long range Coulomb potentials, whose parameters have been optimized in order that the calculated Raman and IR active phonon frequencies, and lattice parameters match with their experimental values. We find a close correspondence between the values of the IR phonon frequencies of PrMnO3 and CaMnO3, which shows that the substitution of the Pr3+ ions with Ca2+ results in a reduction of the frequency of medium- and high-energy IR phonons, and an increase of the frequency of those of low-energy. Nevertheless, the experimentally obtained IR phonon amplitudes of the two materials appear to be unrelated. A comparative study of the vibrational patterns of these modes reveals that most of them correspond to complex atomic vibrations significantly different from PrMnO3 to CaMnO3 which cannot be assigned only to a given type of vibration (external, bending, or stretching modes). In particular, these results confirm that the structure of CaMnO3 is quite far from the ideal (cubic) perovskite structure.
机译：在300到4 K的温度下，在光声子模的频率范围内研究了正交晶的钙钛矿锰钙钛矿PrMnO3和CaMnO3的红外（IR）反射光谱。 Lorentz模型，并通过与晶格动力学计算结果进行比较，将其分配给Pnma结构的确定振动模式。计算是在壳模型的框架内使用短距离的Born-Mayer-Buckingham和长距离的库仑电势进行的，它们的参数已经过优化，以便计算出的拉曼和IR有源声子频率以及晶格参数与他们的实验相匹配。价值观。我们发现PrMnO3和CaMnO3的红外声子频率值之间存在密切的对应关系，这表明Pr3 +离子被Ca2 +取代导致中能和高能红外声子的频率降低，并且增加了那些低能量的频率。然而，两种材料的实验获得的IR声子振幅似乎无关。对这些模式的振动模式进行的比较研究表明，它们中的大多数对应于与PrMnO3至CaMnO3显着不同的复杂原子振动，这些振动不能仅分配给定类型的振动（外部，弯曲或拉伸模式）。特别地，这些结果证实CaMnO 3的结构与理想的（立方）钙钛矿结构相差很远。

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