Carrier tuning of type-I clathrate single crystals

A method to precisely control the carrier properties for single crystalline type-I clathrate is investigated. Polycrystalline samples are synthesized first according to the theoretical ratio for carrier control, and followed by Ga flux single crystal growth process. The composition of single crystals was determined by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP), and the detailed structure was determined by using high-resolution X-ray diffraction. The carrier type and concentration can be tuned by changing the Ba/Ga composition for Ba8Ga16Ge30 (BGG), while only n-type carrier can be achieved in Sr8Ga16Ge30 (SGG). X-ray diffraction analysis shows that the different occupancy factors of the endohedral chemical species may be the reason for this carrier difference between BGG and SGG. (C) 2009 Elsevier Ltd. All rights reserved.