Effect Of Sintering Process On Thermoelectric Properties Of N-type Mg₃Sb₂ Based Materials

The n-type Mg3Sb2-based thermoelectric material,as a potential medium temperature thermoelectric material,has a low ZT value near room temperature,which limits the improvement of conversion efficiency.In this paper,the n-type Mg3Sb2-based material is taken as the research object.By adjusting the sintering process,such as increasing the sintering temperature and prolonging the sintering time,grain size can be increased so as to reduce the scattering effect of grain boundary on carriers and further improving the thermoelectric property near room temperature.The effects of different sintering process on the thermoelectric properties of Mg3.05(Sb0.3Bi0.7)1.99Te0.01 and MgB2-doped Mg3.17B0.03Sb1.5Bi0.49Te0.01 were systematically studied,and obtained the following research results:For Mg3.05(Sb0.3Bi0.7)1.99Te0.01 material,increasing sintering temperature can not only effectively increase grain size,but also weakens the scattering of grain boundary on carriers and optimizes electrical performance to boost the power factor.In addition,the increased electron concentration suppresses the intrinsic excitation and widens the temperature range of the material's high ZT value.Finally,the sample sintered at 1063 K obtains the highest ZT value of 1.15 and the average ZT value of 0.95 between 300 and 623 K.With the increase of sintering temperature,both the output power density and conversion efficiency increase.When the sintering temperature is 1063 K and the hot-end temperature is 625 K,the maximum output power density and conversion efficiency achieve 3.27 W cm-2 and 10.7%,respectively.For the Mg3.17B0.03Sb1.5Bi0.49Te0.01 sample doped with MgB2,the increased sintering temperature can effectively increase the grain size and weaken the carrier scattering by grain boundary to improve the power factor.However,prolonging the sintering time will reduce the conductivity of the MgB2 doped samples at low temperature and decrease the absolute value of the Seebeck coeff-icient.Therefore,the power factor in the low temperature section is reduced significantly.Together with the decrease of the total thermal conductivity,the ZT value decreases in the low temperature section and increases in the high temperature section after prolonging sintering time.The doping of MgB2 enhances the carrier concentration,which effectively improves the electrical properties of the material at low temperatures.However,the doping of MgB2 causes high thermal conductivity,leading to the results that the ZT value increases in the low temperature section and decreases in the high temperature section.In addition,increasing the sintering temperature is beneficial to boosting the output power density and conversion efficiency of the material.Therefore,when the sintering temperature is 1063 K and the hot-end temperature is 725 K,the maximum output power density and conversion efficiency achieve 4.2 W cm-2 and 13.2%,respectively.