Effects of Ga content on thermoelectric properties of P-type Ba8Ga16+xZn3Ge27-x type-I clathrates

P-type Ba8Ga16+xZn3Ge27−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 Np of p-type Ba8Ga16+xZn3Ge27−x clathrates increases remarkably compared with that of Ba8Ga16Zn3Ge27 compound, which results in the increases of electrical conductivity although carrier mobility μH slightly decreases. The thermal conductivity κ of all samples increases with the increase of Ga content. Ba8Ga16.2Zn3Ge26.8 compound exhibits the highest ZT value of 0.43 at 700 K, which is increased by 13% compared with that of Ba8Ga16Zn3Ge27 compound.