Fujioka Yukari, Frantti Johannes, Kakihana Masato
Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.
J Phys Chem B. 2006 Jan 19;110(2):777-83. doi: 10.1021/jp054861b.
Polycrystalline Ba2MnWO6 (BMW) and Sr2MnWO6 (SMW) samples were studied between 80 and 1200 K by Raman scattering spectroscopy. In the case of BMW (space group Fmm), four Raman active vibrational modes, predicted by factor group analysis, were identified. Raman scattering studies with different wavelengths revealed a resonant bands between 300 and 800 cm-1. The origin of these bands was related to the Franck-Condon process. Line broadening versus temperature and phonon frequency were studied, and a qualitative explanation was proposed. SMW samples had considerably more complex Raman spectra. It was found that SMW transformed from tetragonal (room-temperature space group P42/n) to the cubic phase between 670 and 690 K; the phase transition temperature was dependent on sample preparation conditions, and it was considerably lower than in the case of large grain size powders. The role of grain size in phase transition is discussed. Mn ions were found to have a crucial role in the lattice dynamics of both materials.
采用拉曼散射光谱对多晶Ba2MnWO6（BMW）和Sr2MnWO6（SMW）样品在80至1200 K温度范围内进行了研究。对于BMW（空间群Fmm），通过因子群分析预测的四种拉曼活性振动模式被识别出来。不同波长的拉曼散射研究揭示了在300至800 cm-1之间的共振带。这些带的起源与弗兰克-康登过程有关。研究了线宽随温度和声子频率的变化，并提出了定性解释。SMW样品的拉曼光谱要复杂得多。发现SMW在670至690 K之间从四方相（室温空间群P42/n）转变为立方相；相变温度取决于样品制备条件，且远低于大晶粒尺寸粉末的情况。讨论了晶粒尺寸在相变中的作用。发现Mn离子在两种材料的晶格动力学中都起着关键作用。
