Observation of rattling vibrations in clathrate under high pressure and low temperature

Abstract

An experimental system for low-frequency Raman measurements at low temperatures and high pressures was constructed in order to research low frequency vibrations of guest atoms in guest-host materials such as semiconductor clathrates. Raman measurements in the range to 10 cm-1 were attained under low temperature and high pressure by arranging a diamond anvil cell fixed on a cryostat in a quasi-back-scattering geometry. Raman spectra of a clathrate compound Eu8Ga16Ge30 were measured using this experimental system. The low frequency Eu vibration so called the rattling vibration located at ∼20 cm-1 was clearly observed under high pressures and low temperatures.