ICT2014 Abstracts

Worldwide efforts to searching for good thermoelectric materials are frequently focusing on normal states in crystalline semiconductors such as Bi₂Te₃, PbTe, clathrates, filled skutterudites, et al. Copper Selenide was a good candidate thermoelectric material years ago, while new study on this system demonstrates that the figure of merit of Cu₂Se comes up to 1.5 at 1000 K with very low thermal conductivity, due to a liquid-like effect of copper ions superionic characteristics. There undergoes a structure phase transition from a monoclinic to cubic around 400 K in Cu₂Se. In this talk, we report detailed TE transport measurements during the phase transition in Cu₂Se and iodine doped Copper Selenide, which was carefully carry out on electrical resistivity and thermopower with newly developed equipment and thermal transport with laser flash method. And we detected significantly abnormal thermoelectric properties with sharply enhanced Seebeck coefficient and electrical resistivity during the phase transitions, while thermal conductivity was rapidly reduced near to critical temperature. This abnormal phenomenon with electron and phonon critical scattering leads to the improvement in zT above 1 during phase transition, a factor of 3 to 7 times larger than the figure of merit of the normal states, and the highest zT climbs up to 2.3 at 400 K. In addition, doping by iodine shifts the transition temperature TC towards to room temperatures from 400 K to 360 K. Also, the extensively improved zT values during the phase transitions were confirmed by measuring the cooling ability in a device with a single-pair of legs.