A First-principles Study On Semiconductor Thermoelectric Materials Of AgKTe,MCoBi?M=Ti,Zr,Hf?,AgIn₅Te₈

In recent years,as a result of the energy crisis and the consequent environmental pollution,the search for sustainable clean energy has become a worldwide challenge.Thermoelectric materials can directly convert thermal energy into electrical energy without any pollution.It is a new energy material with great potential,which has been widely concerned by people.In order to achieve a wider range of thermoelectric applications,the most challenging aspect is to improve the efficiency of thermoelectric materials.Therefore,the search for semiconductor materials with high ZT value is the effective way to obtain high thermoelectric conversion efficiency.Based on the first-principles,we calculate each thermoelectric related transport coefficient of the semiconductor,comprehensively evaluate the thermoelectric conversion efficiency of the materials,and provide a theoretical basis for the experimental design,preparation and improvement of the performance for thermoelectric materials.There are mainly the following aspects of research:Firstly,we investigated the electronic properties of AgKTe by using meta-GGA+MBJ potential based on the density functional theory?DFT?.On this basis,we predict the relaxation time and carrier mobility of the material by using deformation potential theory,and evaluate the electron transport coefficient of the material by combined the semi-classical Boltzmann transport theory,meantime,we also evaluated the lattice thermal conductivity based on the Debye-Callaway model.The results show that AgKTe exhibits a typical direct narrow-band gap semiconductor structure,and the relaxation time of the n-type system is obviously better than that of the p-type system.We also found that for both n-type and p-type systems,the ZT values of AgKTe semiconductor materials could reach 1.7 at room temperature by adjusting carrier concentration,and such ZT value was also higher than some typical room-temperature thermoelectric materials.Therefore,we predicte that AgKTe might become a potentially good room-temperature thermoelectric material,which is worth further experimental research.Secondly,we studied the comprehensive thermoelectric performance of MCoBi?M=Ti,Zr,and Hf?.The phonon dispersion curves of the MCoBi three systems are calculated.No imaginary mode phonon in the phonon dispersion,which indicates they have well dynamic stability.Then,GGA+PBE method was used to study their electronic structure properties,and it was found that all the three MCoBi systems presented indirect semiconductor characteristics.After that,we further calculated the electronic transport coefficient of MCoBi,and found that M element significantly affected the electronic transport property of MCoBi,especially for their n-type system.In addition,Slack model is used to evaluate the lattice thermal conductivity of MCoBi based on the elastic property of the system.The overall results show that the p-type system of MCoBi has better thermoelectric performance than the n-type system.Among them,the p-type ZrCoBi reaches the maximum ZT value of 1.7 at 800K,and the maximum ZT value of p-type TiCoBi and HfCoBi is 1.4 and 1.5,respectively.This provides a valuable reference for the design and development of efficient MCoBi compound thermoelectric materials.Finally,we investigated the electronic structure property and thermoelectric transport performance of AgIn₅Te₈ based on DFT,combined with semi-classical Boltzmann theory,deformation potential theory and Slack model.We found that the anisotropic behavior of electricity and heat transport of AgIn₅Te₈ supported the observed phenomenon in the experiment,and the calculated lattice thermal conductivity was in good agreement with the experimental value.Finally,by adjusting carrier concentration and temperature,p-type AgIn₅Te₈ can obtain the maximum thermoelectric figure of merit of 2.28 in the direction of xx.The results of this paper provide a theoretical basis for further research on the thermoelectric performance of AgIn₅Te₈,and more ideas for improving the thermoelectric conversion efficiency of AgIn₅Te₈.