Solid-state thermoelectric technology uses electrons or holes as the working fluid for heat pumping and power generation and offers the prospect for novel thermal-to-electrical energy conversion technology that could lead to significant energy savings by generating electricity from waste industrial heat.The key to the development of advanced TE technologies is to find highly efficient TE materials.In current commercial materials,the zTs are limited to values around unity.Recently,several novel concepts have been proposed to enhance the efficiency of TE materials and laboratory results suggest that high zT values can be realized in several families of bulk materials.In this presentation,the thermoelectric properties of bulk copper chalcogenides(Cu2-δX)are reported in a wide temperature range,where X could be S,Se,or Te.We will show these materials possess extremely abnormal thermoelectric properties with very low thermal conductivity and good thermoelectric figure of merit.In particularly Cu2-δSe is taken as an example to demonstrate the abnormal properties of the low temperature phase,the high temperature phase,and the transition states during the phase transitions.The physical mechanisms behind these abnormal thermoelectric properties will also be discussed to show the possibility of realization of ultrahigh thermoelectric figure of merit.