Raman scattering investigation ofRB6(R=Ca,La, Ce, Pr, Sm, Gd, Dy, …

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.