Effects of Ga content on thermoelectric properties of P-type Ba₈Ga_{16+ x} Zn₃Ge_{27− x} type-I clathrates

摘要

P-type Ba₈Ga_16+x Zn₃Ge_27−x (x = 0.1, 0.2, 0.3, and 0.4) type-I clathrates were synthesized by combining solid-state reaction with spark plasma sintering (SPS) technology. The effects of slight increase of Ga content on thermoelectric properties have been investigated. The results show that at room temperature the carrier concentration N _p of p-type Ba₈Ga_16+x Zn₃Ge_27−x clathrates increases remarkably compared with that of Ba₈Ga₁₆Zn₃Ge₂₇ compound, which results in the increases of electrical conductivity although carrier mobility μ _H slightly decreases. The thermal conductivity κ of all samples increases with the increase of Ga content. Ba₈Ga_16.2Zn₃Ge_26.8 compound exhibits the highest ZT value of 0.43 at 700 K, which is increased by 13% compared with that of Ba₈Ga₁₆Zn₃Ge₂₇ compound.