Raman scattering investigation of Pr-based filled skutterudites

Temperature, pressure, and magnetic field dependence of the Raman scattering spectra of Pr-based filled skutterudites PrFe₄P₁₂ and PrOs₄Sb₁₂ have been measured. In the insulator phase of PrFe₄P₁₂ under a pressure, an additional peak is observed. On the other hand, in the A-phase below T=6.5 K at ambient pressure, no additional peak is observed. By means of a factor group analysis, we have evaluated the crystallographic symmetry of the insulator and A-phases as Immm and R3, respectively. In the spectra of PrOs₄Sb₁₂, the crystal field excitation and Einstein oscillations of Pr ion are observed in addition to the first order Raman active phonons. The Einstein oscillation is observed in the second-order Raman scattering spectrum owing to a strong anharmonicity of Pr vibration with the large displacement.