Thermoelectric Properties Of The Doped CdO And The Ca₃Co₄O₉ Co-doped With Sm,Ni And Fe

Thermoelectric material is a kind of material which can be used to realize the direct transformation between electric energy and heat energy by the using internal carriers movement in solid. The current development of thermoelectric material and the fundamental theory about thermoelectric materials were reviewed and discussed in this dissertation. In the present work, the synthesis and characterization of properties about doped CdO and Sm, Ni, Fe co-doped Ca3Co4O9+δ oxides thermoelectric materials were studied. The influences of reaction process, the doped quantum on their properties and the possible mechanism were discussed.Cadmium oxide and Ca3Co4O9 based thermoelectric materials had been prepared by the solid state reaction sintering method and the self propagating method respectively. X-ray diffraction analysis, thermoelectric performance test and cross section scanning analysis were carried out on the prepared materials. The main achievements are listed as followings:(1)The solid state reaction method was used to prepare oxide thermoelectric materials Cd1-xSmxO (x=0,0.001,0.005,0.01,0.05), Cd1-XYxO (x=0,0.005,0.01,0.02); Ca2.95Sm0.05Co3.995-xNi0.005FexO9+δ (x=0,0.10,0.15,0.20) powders were successfully synthesized by the self propagating method, then the bulk materials were prepared by powder metallurgy technology.(2)X-ray diffraction analysis of Cd1-xSmxO indicated that the solubility limit of Sm3+ ion was small, Sm2O3 existed with x value of 0.05. The test results showed that with the increase of Sm content, the density the resistivity and Seebeck coefficient decreased, but the total thermal conductivity increased. Cd1-xSmxO materials achieved higher thermoelectric properties at 973K, the power factor reached 6.68 × 10-4 Wm-1 K-2 and the figure of merit was 0.24 with x value of 0.005.(3)Through the analysis of the performance test of Cd1-xYxO, the density of the samples decreased with the incorporation of Y elements. The resistivity got the minimum value 3.3μΩ·m with the amount of Y doped 0.01. The Seebeck coefficient increased with the increase of temperature, and decreased with the increase of Y content. The thermal conductivity increased with the incorporation of Y3+. The best thermoelectric performance was obtained at 973K with x value of 0.005, the power factor was 2.9 × 10-3 Wm-1 K-2 and the ZT value achieved 0.35.(4)The preparation and analysis of Ca2095Sm0.05Co3.995-xNi0.005FexO9+δ results showed that synthetic powder particle size distribution in 0.2μm to 91.2μm, average particle size of 23.1 μm and more thick. The shape data of this system were in good agreement with the Huang Peiyun equation, the nonlinear exponent m was 2.074, and the modulus of compaction was 1.86MPa. The conductivity and Seebeck coefficient increased with the increase of temperature, but the thermal conductivity decreased. The maximum power factor value P was 3.20 × 10-4 Wm-1 K-2, and ZT value reached 0.13 at 973K with x value of 0.1.