Preparation And Performance Optimization Of AgSbSe₂-based Thermoelectric Materials

Thermoelectric material is a kind of functional material that can realize the mutual conversion between heat and electricity.It has great application prospects in the fields of waste heat recovery and utilization,solid-state refrigeration and so on.AgSbSe₂shows promising for thermoelectric material in the middle temperature region due to the advantage of a extremely low thermal conductivity,a large Seebeck coefficient and the lead/tellurium-free components.However,the intrinsic low carrier concentration leads to poor electrical transport properties of AgSbSe₂,which makes its thermoelectric performance low.In this paper,AgSbSe₂-based thermoelectric materials,prepared by vacuum melting+quenching in air+annealing+hot-press sintering,are used as the research object.Different methods are used to increase the carrier concentration to improve the electrical transport properties of AgSbSe₂,thus making a great enhancement of thermoelectric performance.The main contents of this paper are as follows:1.Ag vacancies are introduced for the first time to optimize the carrier concentration of AgSbSe₂,and the influence of Ag vacancies on the electrical-and thermal-transport properties of AgSbSe₂is investigated.After the introduction of Ag vacancies,the carrier concentration of the Ag_1-xSb Se₂(x=0.005-0.025)sample increases and its resistivity decrease significantly,and consequently the electrical transport property has a considerable improvement.At the same time,the introduced vacancies can form high-frequency phonon scattering center,which is beneficial to reduce the lattice thermal conductivity of AgSbSe₂.The final Ag_0.98Sb Se₂sample achieved the best ZT value of 1.02 at 673 K.2.The effects of Cu and Ag doping on the thermoelectric properties of AgSbSe₂were studied.It is found that the carrier concentration of AgSbSe₂increases with the substitution of Cu/Ag for Sb,and the intrinsic resistivity of AgSbSe₂decreases obviously,and the thermoelectric properties of AgSbSe₂are greatly improved.The results show that the best ZT value of Ag Sb_0.98Cu_0.02Se₂reaches?1.17 at 673 K,which is 4.9 times higher than that of the matrix.Ag_1.015Sb_0.985Se₂achieves the highest ZT value of?1.15(@673 K)and the average ZT value of 0.71(300-673 K).We compared and analyzed the Cu/Ag doped AgSbSe₂samples by the method of single parabolic(SPB)model fitting and first-principles calculation.We found that the thermoelectric properties of Ag doped samples were improved more obviously when the doping concentration was the same compared with that of Cu-doped samples.Based on SPB model calculation,we analyzed the transport characteristics of Cu/Ag doped AgSbSe₂samples.The results show that Ag doped AgSbSe₂samples have relatively low carrier effective mass and lower polarity,and thus the higher mobility when the carrier concentration is similar.Therefore,better electrical transport performance is obtained.At the same time,the point defects introduced by doping enhance the phonon scattering,so that the lattice thermal conductivity of the lattice is slightly optimized.The thermoelectric properties of Cu and Ag doped samples are improved significantly due to the optimization of thermal and electrical transport.