Eur. Phys. J. Appl. Phys. (2013) 64: 30101
https://doi.org/10.1051/epjap/2013130254

Preparation and study of the structural and electronic properties of the type-I clathrate phase Ba₈Ga₁₆Mg_xGe_30-x

¹ College of Optoelectronic Engineering, Yunnan Open University, Kunming, Yunnan Province 650223, P.R. China
² Education Ministry Key Laboratory of Renewable Energy Advanced Materials and Manufacturing Technology, Yunnan Normal University, Kunming, Yunnan Province 650092, P.R. China
³ Department of Applied Physics, Chongqing University, Chongqing 400044, P.R. China

^a e-mail: lidecong666888@126.com

Received: 25 May 2013
Revised: 2 October 2013
Accepted: 9 October 2013
Published online: 9 December 2013

Abstract

Polycrystalline Ba₈Ga₁₆Mg_xGe_30−x compounds were synthesized by combining solid-state reaction with spark plasma sintering (SPS) method. The structural and electronic properties of Mg-substituted Ge type-I clathrate phase Ba₈Ga₁₆Mg_xGe_30−x (x = 1, 2, 3, 4) were investigated experimentally and theoretically. Theoretically structural and electronic properties of Ba₈Ga₁₆Mg_xGe_30−x were calculated by first-principles method based on the density-functional theory. The results indicate a strong preference for the occupation of the 6c sites by Mg. It is found that Mg substitution for Ge can lower the melting points and bulk modulus of this system. The formation energies and the binding energies decrease with increasing Mg content, suggesting that the Mg-doped Ba₈Ga₁₆Ge₃₀ clathrates are stable in a limited range of composition. The calculated results show that these alloys are all indirect gap semiconductors and the values of band gap increase with the increase of Mg content. All specimens exhibit the behavior of the p-type conduction, which is originated from the presence of a shallow acceptor energy level. The electrical conductivity and the room-temperature carrier mobility decrease with increasing Mg content, while the room-temperature carrier concentration increases with increasing Mg content.