Investigation On The Thermoelectric Properties Of MnSe-based Semiconductors

As a new type of green energy conversion material,thermoelectric(TE)semiconductor materials can realize the direct conversion between electric energy and waste thermal energy,and have huge development potential in fields such as thermoelectric cooling and thermoelectric power generation.Studies have shown that Mn Te-based binary transition metal chalcogenide thermoelectric materials can obtain outstanding thermoelectric transport performance in the middle temperature range after a series of optimization designs.In order to further reduce the cost of commercial manufacturing and consider environmental factors,this article focuses on the thermoelectric properties of its alternative derivative,called MnSe.MnSe-based compounds have many excellent characteristics such as abundant reserves of constituent elements,simple preparation and non-toxicity,which makes it possible to become a medium-temperature thermoelectric semiconductor material for research.Unfortunately,pristine MnSe is a wide band gap semiconductor and its intrinsic carrier concentration is at an extremely low level,which makes its electrical transport performance very poor.Based on a brief introduction to the preparation process of MnSe-based compounds,this article uses defect engineering and band engineering strategies to adjust the carrier concentration of the matrix through single-element Ag atom doping in order to advance its PF and thermoelectric performance.In addition,the thermoelectric properties of the MnSe and Sb₂Te₃ composite system were also studied.The main contents of this paper are as follows:(1)The effects of Ag doping on pristine MnSe's phase composition,microstructure and thermoelectric properties have been studied.A series of samples with different Ag doping were prepared by vacuum melting method combined with spark plasma sintering(SPS)technology.The nominal stoichiometric ratio is Ag_xMn_1-xSe(x=0,0.01,0.02,0.03,0.04,0.05).The results show that Ag atoms can be successfully doped into the MnSe lattice during the melting process,and its content reaches saturation at about 3 at.%,and then the excess Ag will react an in-situ process during the cooling stage of melting to generate a small amount of Ag₂Se nano-second phase.The doped-Ag in Mn sites can effectively reduce the band gap of the pristine MnSe,and at the same time,it can introduce more vacancies to reduce its resistivity and achieve a greater increase in power factor.Finally,the maximum figure of merit value of 0.22 at 650 K was obtained at the Ag doping level of 3 at.%,which is significantly improved compared to the base substrate.(2)The effect of MnSe composite with Sb₂Te₃'s phase composition,microstructure and thermoelectric properties have been studied.The(MnSe)_1-x(Sb₂Te₃)_x(x=0,0.10,0.12,0.14,0.16,0.18,0.20)composites were prepared using the similar process as above.The addition of the composite phase Sb₂Te₃ can reduce the sintering temperature of the sample from 800?to 550?,so even at a relatively low temperature,a dense sample with low porosity(relative density of the sample>95%)can be sintered?Due to the higher carrier concentration of intrinsic Sb₂Te₃,the addition of Sb₂Te₃ can form a high-speed channel for carrier transport in the MnSe matrix,and ultimately achieving a lower resistivity and high power factor.Moreover,the intrinsic low lattice thermal conductivity of Sb₂Te₃ makes the thermal conductivity of the composites slightly lower than that of the matrix.Finally,Sample(MnSe)_0.8(Sb₂Te₃)_0.2 achieved the maximum figure of merit value of 0.07 at 800 K,which was also improved compared to the matrix.