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Raman study of phonons in CaMn_7O_(12): Effects of structural modulation and structural transition

机译：CaMn_7O_（12）中声子的拉曼研究：结构调制和结构转变的影响

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摘要

Polarized Raman spectra of oriented CaMn_7O_(12) single crystals have been studied in a broad temperature range (5-500 K) covering the crystallographic, ferroelectric, and magnetic transitions. From the spectra obtained at room temperature (RT) 10 out of the total 12 Raman active 6A_g + 6E_g modes of the trigonal R3 phase have been identified and assigned to definite atomic motions in close comparison to results of lattice-dynamics modeling. With the decrease in temperature below 250 K some Raman bands split, and additional spectral features, not expected for the R3 structure, arise well above the magnetic transitions near 90 and 50 K. Their appearance, however, correlates with the transformation due to incommensurate structural modulation revealed by recent x-ray and neutron-diffraction studies. As temperature increases above RT the intensity of the Raman lines strongly decreases, and entering the high-temperature Im3 phase the spectrum transforms its shape to that expected for a structure with disordered Jahn-Teller distortions.
机译：取向CaMn_7O_（12）单晶的极化拉曼光谱已在涵盖晶体学，铁电和磁跃迁的较宽温度范围（5-500 K）中进行了研究。从室温（RT）获得的光谱中，已识别出三角R3相的全部12个拉曼活性6A_g + 6E_g模式中的10个，并与晶格动力学建模结果进行了比较，并将其分配给确定的原子运动。当温度降低到250 K以下时，一些拉曼能带分裂，R3结构未预期的其他光谱特征会在高于90和50 K的磁跃迁上方出现。但是，由于结构不相称，它们的出现与转换有关最近的X射线和中子衍射研究揭示了这种调制。当温度升高到高于RT时，拉曼线的强度会大大降低，并进入高温Im3相，光谱的形状会转变为Jahn-Teller畸变结构的预期形状。

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  • 来源
    《Physical review》 |2014年第21期|214302.1-214302.6|共6页
  • 作者

    M. N. Iliev; V. G. Hadjiev; M. M. Gospodinov; R. P. Nikolova; M. V. Abrashev;

  • 作者单位

    Texas Center for Superconductivity and Department of Physics, University of Houston, Houston, Texas 77204-5002, USA;

    Texas Center for Superconductivity and Department of Mechanical Engineering, University of Houston, Houston, Texas 77204-5002, USA;

    Institute of Solid State Physics, Bulgarian Academy of Sciences, 1184 Sofia, Bulgaria;

    Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria;

    Instituto de Fisica, UFRGS, Porto Alegre, 91501-970 Rio Grande do Sul, Brazil,Faculty of Physics, University of Sofia, 1164 Sofia, Bulgaria;

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  • 关键词

    infrared and raman spectra; transition-metal compounds; theory, models, and numerical simulation;

    机译：红外和拉曼光谱;过渡金属化合物;理论;模型和数值模拟;

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