The Optimization Studies On Thermoelectric Properties Of β-Cu₂Se By CuGaSe₂ And M（M=Zn, Ni, Fe, In, Sm）Doping

With the energy crisis and the increasing environment problem, thermoelectric（TE） materials can realize conversion between thermal energy and electric energy, and it plays an more and more important role, and attracts the attentions of the researchers as a kind of environmentally friendly new energy materials. β-Cu₂ Se is a kind of p type potential thermoelectric materials with a very complex crystal structure, and a kind of “electronic crystal- phonon glass” material with a good electric conductivity and a low thermal conductivity. The very low lattice thermal conductivity owns to the highly disordered copper ions around the Se sublattice and super ionic with liquid-like mobility in the β-Cu₂Se crystal structure. In this thesis, CuGaSe₂ was introduced into β-Cu₂ Se as the second phases and five kinds of element（Zn, Ni, Fe, In, Sm） were doped at Cu site. The effects on crystal structure and thermoelectric performance of β-Cu₂Se compounds was investigated.For serials of（Cu₂Se）₁-x（CuGaSe₂）_x samples, the experimental results show that the dissolved Ga in the crystal structure of β-Cu₂ Se reduced the resistivity, optimized the powder factor and reduced the thermal conductivity, and further improved the thermoelectric figure of merit of β-Cu₂Se. But the Cu GaSe₂ phase significantly increased the resistivity and thermal conductivity, with the negative effects on the TE performance of β-Cu₂Se. The sample of x = 0.0075 has the highest z T value among these samples. It reaches 1.4 at 823 K,is about 39.7% improvement comparing to the value of the un-doped sample.For the Cu₁.99A₀.01Se（A = Zn, Ni, Fe, In, Sm） samples, the doping of A except the In resulted in the decrease of resistivity, owning to the increase of the carrier concentration and the decrease of the carrier mobility, thus the improvement of the powder factor, and the thermal conductivity of the samples decreases except In doping. Ni is the most effective doping element among these to the improvement of z T.The lattice parameter of β-Cu₂Se is decreased due to the replacement of Cu by Ni, and is increased due to the replacement of Cu by Sm. Doping of Ni or Sm increased the resistivity of the sample significantly, owning to the increase of the carrier concentration and the decrease of the carrier mobility, and the powder factor is optimized. Moreover, the lattice thermal conductivity of all samples decreased by Ni or Sm doping. The sample of x = 0.0075 has the highest z T value among the Ni-doping samples, it reaches 1.51 at 823 K. The sample of x = 0.015 has the highest z T value among the Sm-doping samples, it reaches 1.17 at 823K...