Thermoelectric properties of Mo/sub 6/Se/sub 8/-based chevrel phase with semiconducting properties

Mo/sub 6/Se/sub 8/-based Chevrel phase compounds with inserted cations into cavities are interesting as a new candidate of PGEC (Phonon Glass Electron Crystal) thermoelectric materials. From band structure calculations, the compositions including TiMo/sub 6/Se/sub 8/ have been found to be semiconductor or semimetal, and therefore are expected to have good Seebeck coefficient besides low thermal conductivity. However it had been apparent that insertion of enough cations to the cavities in Mo/sub 6/Se/sub 8/ with simple process was difficult due to secondary phase and oxide appearance. We present in this paper an estimation of the effect of two inserted cations experimentally and theoretically in order to improve thermoelectric properties of Chevrel phases. The thermoelectric properties are significantly enhanced by Cu-addition, and the dimensionless figure of merit, ZT=0.22 is estimated for nominal Cu/sub 0.3/Ti/sub 1.0/Mo/sub 6/Se/sub 8/ sample at 800/spl deg/C. It is found from band structure calculations by the self-consistent Korringa-Kohn-Rostoker (KKR) method that the Fermi level tends to shift to upper state by Cu-addition. Cu-addition can compensate a loss of Ti and control carrier concentration instead of Ti.