Raman spectroscopy of type-I and type-VIII silicon clathrate alloys Sr8AlxGa16−xSi30

Raman spectra of type-I and type-VIII silicon clathrates have been measured at ambient temperature and pressure for Sr8AlxGa16−xSi30 alloys prepared by changing the Al/Ga ratio. Although the broadening of Raman bands appeared, due to the disorder of the host framework by replacing the Si sites by Al and Ga atoms, the phase transition from type-I to type-VIII (x=fromx=from 7 to 8) was confirmed from the following changes; in type-VIII phase, (1) Sr guest vibrations shift toward higher frequencies by the decrease in the size of host cage and (2) the appearance of sharp and strong peak of Sr vibration at about 75 cm−1. All Sr vibrational frequencies are consistently compared with the Einstein temperatures estimated from the atomic displacement parameters (ADPs) in X-ray diffraction (XRD) data.