Preparation And Thermoelectric Properties Of Cu₂Se Based Compounds

Over the past decade there has been heightened interest in the field of thermoelectric materials and related thermoelectric energy conversion applications due to the facts that thermoelectric materials can convert thermal energy directly into electrical energy, and in addition they accomplish this without any moving parts or greenhouse gas emissions. With good electrical properties and an inherently complex crystal structure, Cu2-xSe is a potential "phonon-glass electrion-crystal" (PGEC) thermoelectric material that has previously not attracted much interest. The crystal structure of Cu2-xSe compounds has beed intensively investigated due to its complexity. However, the thermoelectric transport properties of Cu2-xSe compounds has not yet been sysmeticly investigated. Therefore, in order to develop the application for Cu2-xSe based thermoelectric materials, we sysmeticly investigate the thermoelectric transport properties and phase transition of Cu2-xSe compounds in the temperature range of 300-800 K.In this thesis, Cu2-xSe bulk materials with different Cu content have been successfully prepared by melting-quenching method combining with spark plasma sintering. The effect of Cu content on the thermoelectric transport properties and phas transition of Cu-poor Cu2-xSe (0≤x≤0.25) and Cu-rich Cu2+xSe (0≤x≤0.04) compounds have been studied. The measurement results show that Cu2.o4Se compound possess the best thermoelectric properties. Based on that results, we chose S as doping element and investigated the effect of S content on the thermoelectric properties of Cu2.04Se1-δSδ(8=0,0.01,0.03,0.05) compounds.The XRD results show that the Cu2-xSe compounds with Se at% of 33.3-33.8% possessα-phase (monoclinic) and the Cu2-xSe with Se at% of 35.3-36.4% possess mix phases of theα-phase (monoclinic) and theβ-phase (cubic) at the room temperature. With increase of Cu content, the temperature ofα-βphase transition inceases. When x=0, the phase transition temperature is about 373 K; and when the temperature is higher than 373 K, the Cu2Se compound will possess single p-phase structure. For the Cu-rich Cu2+xSe (0≤x≤0.04), the x shoud be less than 4%, otherwise Cu particles will be observed on the surface of melting ingots. The Cu-rich Cu2+xSe (0