Study On The Process For The Preparation And Thermoelectric Properties Of Cazn₂Sb₂Based Zintl Phase Thermoelectric Materisls

Zintl compound CaZn₂Sb₂is one of the most promising thermoelectric materials forits high Seebeck coefficient and high electrical conductivity. These two parameters arecritical in determining the ability of the a compound converting heat into electricity.Moreover, due to its simple structure, we can reduce its thermal conductivity by dopingand substituting.In this thesis, through the control of temperature, time and pressure, high pressuresintering （HPS） combining with Spark Plasma Sintering （SPS） methods were employed tocalcine and sinter Ca pieces, Zn powder and Sb powder stoichiometric mixture （1:2:2）.X-ray power diffraction and scanning electron microscopy （SEM） were used for structuralanalysis. The CaZn₂Sb₂bulk compounds were synthesis as following steps: HPS at first950℃for30min, and then second HPS at30hrs under pressure4GPa, the resulting bulkswere gound and SPS at650℃for30min. By analysis of the TE properties for thesamples with the2ndHPS sintered at680℃,850℃,900℃respectively, it is concludedthat high pressure sintering can improve the material’s electrical performance, and highpressure sintering to change lattice thermal conductivity effect is not obvious.Comparing the SPS samples for the axis of parallel with that of perpendicular to thedirection of pressure, the SPS unidirectional pressure sintering CaZn₂Sb₂resistivity hasobvious orientation, Seebeck coefficient and thermal conductivity has weak orientation,perpendicular to the pressure shaft direction ZT value in the whole temperature interval ishigher than the parallel pressure shaft direction ZT value.By analysing the TE parameters of CaZn₂Sb₂prepared with the traditional meltingmethod and HPS+SPS method, although ZT of the latter reaches the highest value0.54at740℃lower than the former reaches0.56, the preparation period of the novel HPS+SPSmethod was remarkably shortened from7to8days by traditional method to less than5hours, and can ensure the CaZn₂Sb₂material in the medium temperature area goodapplication.