Raman scattering investigation of RB6 (R=Ca, La, Ce, Pr, Sm, Gd, Dy, and Yb)
Raman scattering investigation of RB6 (R=Ca, La, Ce, Pr, Sm, Gd, Dy, and Yb)
复制标题
DOI：
10.1103/physrevb.68.224305
复制
发表时间：
2003-12
影响因子：
3.7
通讯作者：
N. Ogita;S. Nagai;N. Okamoto;M. Udagawa;F. Iga;M. Sera;J. Akimitsu;S. Kunii
中科院分区：
文献类型：
--
作者：
N. Ogita;S. Nagai;N. Okamoto;M. Udagawa;F. Iga;M. Sera;J. Akimitsu;S. Kunii
测量了 RB 6 晶体（R=Ca 2 + 、La 3 + 、Ce 3 + 、Pr 3 + 、Sm 2 . 6 + 、Gd 3 + 、Dy 3 + 和 Yb 2 + ）的拉曼散射光谱的激发能、偏振和温度依赖性。在CaB 6 和YbB 6 的二价晶体中，Eg声子显示双峰，而对于三价情况，线形是宽的单峰。在三价晶体中，除了拉曼活性声子和晶体电场（CEF）激发之外，在200 cm - 1 附近和1400 cm - 1 附近清晰地观察到两种额外峰。 200 cm - 1 附近的峰强度显示出随着温度降低而异常降低，并且这种温度依赖性与 R 离子的均方位移相关。此外，由于B 6 ，它们的能量随着笼空间的增加而降低。这些峰源自声学声子的二阶激发。 1400 cm - 1 附近的宽峰被指定为 T 2 g 声子的二阶激发。对于T 2 g声子，三价和二价晶体之间的能量差及其线形变化表明电子-声子相互作用的存在。我们观察到了 PrB 6 中的 CEF 激发，并获得了 x=0.94 和 W=9.2 K 的 Lea、Leask 和 Wolf 参数。
The excitation-energy, polarization, and temperature dependeces of Raman scattering spectra have been measured for the RB 6 crystals (R=Ca 2 + , La 3 + , Ce 3 + , Pr 3 + , Sm 2 . 6 + , Gd 3 + , Dy 3 + , and Yb 2 + ). In the divalent crystals of CaB 6 and YbB 6 , the Eg phonon shows doublet, while the line shape is a broad single peak for the trivalent case. In the trivalent crystals, two kinds of the extra peaks have been clearly observed at around 200 cm - 1 and at around 1400 cm - 1 in addition to the Raman-active phonons and crystal electric-field (CEF) excitations. The peak intensities at around 200 cm - 1 show the anomalous decrease with decreasing temperature, and this temperature dependence correlates with that of the mean-square displacement of the R ion. Furthermore, their energies decrease with the increase of the cage space due to B 6 . These peaks are originated from the second-order excitation of acoustic phonons. The broad peak at around 1400 cm - 1 is assigned as the second-order excitation of the T 2 g phonon. For the T 2 g phonon, the energy difference and its line-shape change between the trivalent and divalent crystals suggests the existence of electron-phonon interaction. We have observed the CEF excitation in PrB 6 and have obtained the Lea, Leask, and Wolf parameters with x=0.94 and W=9.2 K.