Raman spectroscopy study of type-I clathrates A8Sn44□2 (A = Rb, Cs) and Rb8Hg4Sn42

Vacancy(□)-induced localized Raman bands around 70 cm−1 were observed at ambient conditions for the group-14 defect-stabilized type-I Rb8Sn44□2 and Cs8Sn44□2 clathrates as indicated by the vertical arrows; no such bond occurs in the defect-free Rb8Hg4Sn42 clathrate.