Structural and Electronic Properties of Type I Clathrates M8Ga16Ge30 (M = Ba, Sr, Yb) from First-Principles Calculations

In this work, the effects of filling atoms on the structural and electronic properties of type I clathrates M8Ga16Ge30 (M = Ba, Sr, Yb) have been investigated by first-principles calculations. It is found that these alloys are all indirect-gap semiconductors, among which Yb8Ga16Ge30 possesses the smallest band gap and the largest bulk modulus, and a unique feature of a sharp peak in the density of states (DOS) near the Fermi level, implying good potential as a thermoelectric material for band engineering. Moreover, calculations indicate direct chemical bonds between Yb and the nearest host Ga/Ge atoms, which can play an important role in the reduction of the lattice thermal conductivity via large off-center rattling of the Yb in the larger cage of the clathrate structure, suggesting that Yb8Ga16Ge30 is of interest for future thermoelectric applications.