Heat capacity studies on rattling vibrations in Ba–TM–Ge type I clathrates Original Research Article

Type I clathrates have a cage structure formed by IV group elements and can encapsulate alkali or rare alkali atoms inside the cages. The potential inside the cages strongly depends on the cage formation and encapsulated atoms. In this paper, we studied the heat capacity of Ba–TM–Ge clathrates. We found that with increase of the disorder in the framework, the lattice constant increases, giving larger free space inside the cages. This change decreases the Einstein energies of the encapsulated atoms and increases the rattling states.