Temperature-dependent influence of disorder on the thermodynamic properties of Sn20.5□3.5As20I8, a vacancy-driven superstructure of the type-I clathrate

A polycrystalline sample of the Sn20.5□3.5As22I8 clathrate was synthesised by a standard ampoule method from elements. Temperature dependencies of the heat capacity Cp(T) and unit cell parameter a(...