Clathrates are extraordinary thermoelectric materials due to their low thermal conductivity. However, it is generally assumed that the atoms captured in the cages, so-called the guests, act as “rattlers” inducing disordered lattice dynamics and unusual thermal properties. Here, the isotope Ge-76 has an evident influence on the phonons and the heat capacity of Ba8Ga16Ge30 (BGG) by using ab initio lattice dynamics calculations. The results verify the intense coupling between the guest and host lattice which contributesto the anomalous specific heat. This finding paves the way for understanding the microscopic mechanism of clathrates and designing the thermoelectric materials with high performance.
