Crystal structure and thermoelectric properties of the type-I clathrate compound Ba8Ge43 with an ordered arrangement of Ge vacancies

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The crystal structure of the type-I clathrate compound Ba8Ge43 has been investigated by x-ray diffraction and transmission electron microscopy. The thermoelectric properties of Ba8Ge43 have also been investigated. The crystal structure of Ba8Ge43 is different from that reported for the usual type-I clathrate compounds with the space group of Pm3¯n but is a superlattice structure based on the usual type-I clathrate structure due to the ordering of Ge vacancies in half the 6c sites of the usual type-I clathrate structure. The crystal structure of Ba8Ge43 belongs to the space group of Ia3¯d and Ge vacancies exclusively occupy the 24c sites. The thermoelectric properties of Ba8Ge43 are not particularly good, as exemplified by the rather low ZT value of 0.057 because of the high value of electrical resistivity, which may arise from the existence of Ge vacancies.