Microstructure And Properties Of Zn-Sb Based Thermoelectric Materials

β-Zn₄Sb₃ is one of the state-of-the-art thermoelectric materials used in medium temperatures,due to its complex structure and low thermal conductivity,but it is hard to preapre becauseof its brittleness.Therefore,the investigations have been made in the present work to improve its thermoelectric properties which involve the works done below:1.The evaluation of ternary Zn_4-xM_xSb(Cu,Al)alloys which were prepared by spark plasma sintering(SPS)technique.Measurements show that a proper Cu substitution for Zn can improve its thermoelectric performance. With molar fraction x increasing from 0 to 0.4,the Seebeck coeffcient of ternary alloys Zn_4-xM_xSb₃ raises rapidly,the maximum dimensionless figure of merit ZT value of 0.7 can be obtained at the temperature of 654 K,being approximate 0.23 higher than that ofβ-Zn₄Sb₃ at the corresponding temperature.2.Zn_4-xCu_xSb_3-xBi_x,alloys with proper Cu and Bi substitutions for Zn and Sb respectively,prepared by the same technology,show superior thermoelectric performance toβ-Zn₄Sb₃.The maximum dimensionless figure of merit ZT of 0.53 is achieved at 574 K atx=0.4.3.Pseudo-bianry alloys(Cu₂Sb)_x(Zn₄Sb₃)_1-xwere prepared and the ZT value of 0.72 for the(Cu₂Sb)_x(Zn₄Sb₃)_1-xalloy with x=0.05 is obtained at 654 K,which is 0.25 higher than that ofun-dopedβ-Zn₄Sb₃.4.Condersidering the fact that a major phase such as ZnSb with low thermoelectric property and a minor phase Cu₅Zn₈ were formed in the Cu₂Sb-added Zn-Sb based alloys,the ZnSb phase can be a determining factor in controlling the thermoelectric properties,the minor phase Cu₅Zn₈ palys an important role in modulating the thermoelectric performance, therefore,Cu₅Zn₈ was specially introduced to form pseudo-binary alloys (Cu₅Zn₃)_x(Zn₄Sb₃)_1-x(x=0.005-0.04)in order to enhance the possibility of the formation of typicalβ-Zn₄Sb₃ phase.The analysis using XRD confirms that a mojor phaseβ-Zn₄Sb₃ is formed after a proper Cu₅Zn₈ addition(x<0.02),a significant thermoelectric performance has been achieved with the ZT value of 0.84 at 636 K,which is approximate 1.8 times that ofβ-Zn₄Sb₃ at the corresponding temperature,proving that the current approach to the determination of the composition of Zn-Sb based alloys is worthing recommendation in improving the medium-temperature thermoelectric properties.