Carrier control in Ba₈Ga₁₆Ge₃₀ single crystals

Carrier control of p and n in type-I crystal clathrates Ba ₈Ga₁₆ Ge₃₀'s (BGG's) is studied for their single crystals. The polycrystalline precursors with regulated various stoichiometric compositions are employed for single crystal growth under excess amount Ga as a flux. Hall coefficient measurements prove that both p and n type BGG single crystals are produced by modifying the relative ratios between the endohedral alkaline-earth atoms and the Ga atoms residing in the framework. ICP analyses together with Rietveld refinement based on the high resolution synchrotron X-ray diffraction suggests that the occupancy of Ba is less than one, and this explains the reason why p type can be possible in BGGs in contrast to the fact only n type is obtained in Sr₈Ga₁₆Ge ₃₀'s. Superconductivity is not observed when the high doping levels are searched.