Tunable charge carriers and thermoelectricity of single-crystal Ba8Ga16Sn30

We have grown single crystals of the type-VIII intermetallic clathrate Ba8Ga16Sn30 from both Sn and Ga fluxes, evaluated their compositions through electron microprobe analysis and studied their transport properties through measurements on the temperature dependent resistivity, thermopower and Hall coefficient. Crystals grown in SIT flux show n-type carriers and those from Ga flux show p-type carriers, whereas all measured compositions remain very close to the stoichiometric 8:16:30 proportion of Ba:Ga:Sn, expected from charge-balance principles. Our results indicate a very high sensitivity of the charge carrier nature and density with respect to the growth conditions, leading to relevant differences in transport properties which point to the importance of tuning this material for optimal thermoelectric performance.