One-Phonon Spectra and Effective Phonon Density-of-States in CaGa2S4
One-Phonon Spectra and Effective Phonon Density-of-States in CaGa2S4
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CaGa2S4 中的一声子谱和有效声子态密度
DOI：
10.7567/jjaps.39s1.307
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发表时间：
2000
影响因子：
1.5
通讯作者：
Kazutoshi Iwai
中科院分区：
文献类型：
--
作者：
N. Mamedov;S. Iida;T. Aoki;A. Kato;M. Yamazaki;N. Yamamoto;T. Shishido;Kazutoshi Iwai
对晶态和非晶态CaGa_2S_4进行了室温拉曼研究。使用高抑制双单色仪和氩离子激光的5 14.5nm谱线在背散射几何结构中获得了斯托克斯和反斯托克斯光谱。除了偏振特性外，多晶CaGa 2 S 4的拉曼光谱在布里渊区的中心代表单声子谱。该谱由18条谱线组成，而不是由因子群分析给出的84条拉曼活性谱线。单声子态密度从ωmin=74.7cm-1到ωmax= 412.7cm-1的分布呈现出199.8cm-1到284.7cm-1的频率间隙。从非晶CaGa 2 S 4的拉曼光谱得到的布里渊区的有效声子态密度与单声子谱的峰密度分布略有不同。CaGa_2S_4中德拜近似的上限为21.7 cm ~（-1）。分子方法的适用性的拉曼光谱的CaGa 2 S 4进行了讨论。研究表明，两种不同的结构单元在频率间隙以上产生最强烈的284.7cm-1和360.7cm-1振动。
Room temperature Raman study of the crystalline and amorphous CaGa2S4 was done. Stokes and Anti-Stokes spectra were obtained in back-scattering geometry using a high rejection double monochromator and the 5 14.5nm line of an argon ion laser. Except for polarization characteristics, the Raman spectra of the polycrystalline CaGa2S4 represent one-phonon spectra at the center of the Brillouin zone. The spectra consist of 18 lines rather than 84 Raman-active lines given by the factor-group analysis. The distribution of the one-phonon density-of-states from ωmin=74.7cm-1 to ωmax=4 12.7cm-1 exhibits a frequency gap between 199.8 cm-1 and 284.7cm-1. The effective phonon density-of-states across the Brillouin zone, which was derived from the Raman spectrum of the amorphous CaGa2S4, exhibits somewhat different distribution of the peak densities compared to one-phonon spectra. The upper limit for Debye approximation in CaGa2S4 is found at 21.7 cm-1. The applicability of the molecular approach to the Raman spectra of CaGa2S4 is discussed. It is proposed that two different structural units generate the most intense 284.7cm-1- and 360.7cm-1 -vibrations above the frequency gap.