The Structure And Thermoelectric Performance Of β-Cu₂Se By The Secondary Phase Incorporating And Elements Doping

Thermoelectric materials(TE) as a new energy materials attract the attention for scientist. The p-type β-Cu2 Se has an inherently complex crystal structure and “phonon-liquid electrion-crystal”(PLEC) characteristics and became a promising TE materials. In this thesis,β-Cu2 Se based alloys were incorporated Sn Se and Cu3 Sb Se3 as the second phases, were substituted Cu with Mn or Se with Te, the structure and TE performance of such serials of samples were investigated in de-tail. The main results are present as below:(1) A small amount of Sn atoms replaced the Cu atoms in the structure of β-Cu2 Se for(Cu2Se)1-x(Sn Se)x(x = 0, 0.01, 0.03, 0.05, 0.07, 0.10) serials of samples, which increased the lattice parameter of β-Cu2 Se, decreased resistivity and Seebeck coefficient owning to the decrease of the carrier concentration. The power factor was optimazed, and lattice thermal conductivity was reduced by subsititution of Cu by Sn. While the Sn Se second phase can increasing the thermal conductivity with negative effects on the TE performance of of β-Cu2 Se. A highest ZT value of 1.41 was achieved for the sample of(Cu2Se)0.97(Sn Se)0.03 at 823 K. which is about 20% higher than that of un-doped β-Cu2 Se sample.(2) A small amount of Sb atoms replaced the Cu atoms in the structure of β-Cu2 Se for(Cu2Se)1-x(Cu3Sb Se3)x(x = 0, 0.003, 0.006, 0.01, 0.015, 0.02, 0.03) serials of samples, which increased the lattice parameter of β-Cu2 Se, decreased resistivity and Seebeck coefficient owning to the decrease of the carrier mobility. The power factor was optimazed, and lattice thermal conductivity even the total thermal conduc-tivity was reduced by subsititution of Cu by Sn. Owning to the low thermal conduc-tivity of Cu3 Sb Se3, the Cu3 Sb Se3 second phase decreased the thermal conductivity of the samples. A highest ZT value of 1.31 was achieved for the sample of(Cu2Se)0.98(Cu3Sb Se3)0.02 at 775 K.(3) The subsititution of Se by Te gradully increased the lattice parameter of β-Cu2 Se, which increased the carrier concentration, reduced resistivity and Seebeck coefficient. But the power factor has not been improved. Meanwhile, doping of Te decreased the lattice thermal conductivity. Due the large increase of carrier thermal conductivity, The subsititution cannot improve the TE performance of β-Cu2 Se.(4) Doping of Mn on Cu reduced the hole carrier concentration of β-Cu2 Se, which resulted in the increase of the resistivity and Seebeck coefficient, and also dra-maticly decreased the lattice thermal conductivity and total thermal conductivity. A highest ZT value of 1.3 was achieved for the sample of Cu1.99Mn0.01 Se at 823 K.