Design And Thermoelectric Properties Of Transition Elements-Containing Metallic Telluride

Many kinds of telluride, such as Bi₂Te₃ and AgSbTe₂ and so on, have received extensive attention and research in thermoelectric materials areas. Metal telluride using in middle temperature area were analyzed in this dissertation. In the present work, Ga-containing telluride, AgSbTe₂ based telluride and InSnTe based telluride were prepared by vacuum smelting and spark plasma sintering techniques, their microstructures and thermoelectric properties were evaluated.Sn-added Ga₂Te₅ based compounds were prepared by spark plasma sintering and their microstructures and thermoelectric properties were evaluated in the temperature range from 319 to 549 K. Through XRD analysis, the main phase Ga₂Te₅, a small amount of SnTe and single element Te were observed. Measurements indicated that the Seebeck coefficients increase and the electrical and thermal conductivities decrease with the temperature in the entire temperature range. The highest thermoelectric figure of merit ZT of 0.16 can be achieved for Ga2SnTe5 at 549 K due to the relatively low thermal conductivity and high electrical conductivity.Ga element replaced Sb in the Ga₂Te₃ alloy with the same molar fraction and Ga1.9Sb0.1Te3 alloy was prepared by spark plasma sintering. Measurements reveal that the maximum Seebeck coefficient of the sample is about 240μV/K, much lower than that of single crystal Ga₂Te₃, and the electrical conductivity decreases from 3600 to 1740Ω^-1·m^-1 with temperature elevation to 649 K, being at least 17 times that of single crystal Ga₂Te₃ at the corresponding temperature. The maximum TE figure of merit (ZT ) value of 0.1 is obtained at 649 K, which is approximately 3 times that of single crystal Ga₂Te₃.The alloys (AgSbTe₂)_x(Sb₂Te₃)_y were prepared using spark plasma sintering techniques. Through XRD analysis, the single phase AgSbTe₂ was observed. Owing to the low lattice thermal conductivity and high electrical conductivity of the compound, the ZT value of x=0.385 smple reaches 1.1 at 547 K,and is approximately 2 times that of Ag_0.365Sb_0.558Te alloy, thus it can be seen thermoelectric performance improving through component proportion slightly adjusted.The pseudo-binary alloy (Ag_0.365Sb_0.558Te)_0.975 (GeTe)_0.025 was prepared using spark plasma sintering techniques and thermoelectric properties were evaluated over the temperature range 318～551K. If in comparison with the transport properties of Ag_0.365Sb_0.558Te, a little higher Seeeck coefficients and lower thermal conductivities were obtained at the no expense of electrical conductivities. The highest thermoelectric figure of merit ZT for the alloy (Ag_0.365Sb_0.558Te)_0.975 (GeTe)_0.025 is 0.69 at 551 K, whereas that of the ternary alloy Ag_0.365Sb_0.558Te is 0.61 at the corresponding temperature.In the present work In₂Te₃–SnTe compounds were prepared and their thermoelectric properties evaluated in the temperature range from 318～705 K. Measurements reveal that the transport properties are strongly dependent on the chemical composition In₂Te₃ content, and lattice thermal conductivity significantly reduces above a minimum In₂Te₃ concentration, which can possibly be explained by an introduction of the vacancy on the indium sublattice and periodical vacancy planes. The highest thermoelectric figure of merit ZT of 0.19 can be achieved at 705 K, and a big improvement of In₂Te₃ based alloys would be expected if a proper optimization to the chemical compositions and structures were made.Al element replaced In element with a given concentration in an In-Sn-Te based alloy and (In_1.9Al_0.1Te₃)_0.08(SnTe)_0.92 compound was prepared. Measurements reveal that although the Seebeck coefficient of the sample is almost unchanged, the electrical conductivity is about twice as much as that of the Al-free (In₂Te₃)_0.08(SnTe)_0.92 alloy at the corresponding temperatures. The highest ZT value of 0.28 was obtained at 668 K, enhancing by about a factor of 5 relative to that of the Al-free (In₂Te₃)_0.08(SnTe)_0.92 alloy at the corresponding temperature.On the side (In_1.9Al_0.1Te₃)_0.09(SnTe)_0.91 compound was prepared. Measurements reveal that the highest ZT value of 0.4 was obtained at 693 K, enhancing by about twice of the Al-free (In₂Te₃)_0.09(SnTe)_0.91 compound at the corresponding temperature.Cu element replaced In element with the same molar fraction in (In₂Te₃)_0.08(SnTe)_0.92 and (In_2-xCu_xTe₃)_0.08(SnTe)_0.92 (x=0.025, 0.05, 0.2) compounds were prepared by spark plasma sintering. Through XRD analysis, the main phase SnTe and second phase In1.15Cu2.29Te4 were observed, without single element Te. Measurements indicated that the electrical conductivity increased significantly and lattice thermal conductivity became very low after Cu-doped. The highest ZT value of 0.28 for the x=0.2 sample was obtained at 647 K, about 4.6 times of the Cu-free (In₂Te₃)_0.08(SnTe)_0.92 compound at the corresponding temperature.