Last five years we have mainly investigated phonons in the following cage compounds by Raman scattering: RT4X12, A 8Ga16Ge30, La3Pd20Ge 6, RB6, KOs2O6. From this systematic investigation we have clarified the following dynamical properties of the guest ion trapped in the large cages. The vibration of the guest ion is highly anharmonic due to weak atomic interaction between the guest ion and cage atom. This anharmonicity universally decreases the vibration energy of the guest ion with decreasing temperature. The existence of carriers decreases the interaction between the guest atoms and changes the dispersion curve of the guest ion mode to flat, which is the experimental evidence of the weak interaction between the guest atoms. For thermoelectricity, it is found in A8Ga 16Ge30 that the off-center rattling decreases lattice thermal conductivity.
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