Preparation And Thermoelectric Performance Optimization Of Fe₂TiSn-based Compounds

Today,with the increasing energy shortage,people pay more attention to clean energy.Among them,thermoelectric materials are well known as a clean new renewable energy material.It has the advantages of low loss,almost no pollution,high reliability,and is expected to greatly improve energy efficiency and thus alleviate environmental pollution.Fe₂TiSn is a member of the full-Heusler alloy and is also predicted to have good room temperature thermoelectric properties.However,the conventional preparation method uses the arc melting method for synthesis,has high energy consumption,long preparation time and certain requirements for instruments and equipment.At the same time,the thermoelectric properties of the synthesized intrinsic samples are poor,mainly due to the lower Seebeck coefficient of the sample and the high thermal conductivity.This limits the practical application of Fe₂TiSn-based full-Heusler alloy in the field of thermoelectricity.In view of the problems in the preparation of Fe₂TiSn-based full-Heusler alloys,this paper firstly optimized the synthesis method.The conventional arc melting synthesis method has high energy consumption and costs long time.In this paper,high-temperature self-propagation synthesis method is adopted,and high-purity Fe,Ti,Sn and other elements are used as raw materials for self-propagation at high temperature,and then the sample is subjected to feed annealing.A single-phase Fe₂TiSn-based full-Heusler alloy was successfully prepared,and the preparation time was shortened from 2 weeks as reported in the original literature to several hours.Since the high temperature self-propagation only needs to be ignited by the hand-held welding torch,the subsequent reaction is completed by itself,thereby greatly reducing the energy consumption.Since the self-propagating reaction produces a large number of non-equilibrium microstructures?nanostructures,gaps,metastable phases?,thereby reducing the thermal conductivity of the sample,a material with better thermoelectric properties can be obtained.The problem of the thermoelectric properties of the Fe₂TiSn-based full-Heusler alloy is based on the previous literature analysis because the band-gap of the Fe₂TiSn-based full-Heusler alloy is too narrow,which is quite different from the theoretical calculation.It boldly predicts that Si can enter the Sn position to generate Fe₂TiSn1-x Si X compound,and then optimize the band-gap to a reasonable value to optimize the Seebeck coefficient of the sample.In this paper,a series of Fe₂TiSn1-x Si Xcompounds were prepared and their thermoelectric properties were characterized.Due to the entry of Si,the Seebeck coefficient of the sample is improved.When the Si ratio is 0.3%,the sample obtains the best ZT value of 0.014,which is about 100%higher than the intrinsic sample.The intrinsic sample was then heavily doped with Co and Ni.The intention is that after the n-type doping according to the band structure,the sample may have a larger Seebeck coefficient.Therefore,a batch of Fe2-2x M2 x Ti Sn?M=Co and Ni,x=0.1,0.2,0.3,0.4,0.5?samples were synthesized by self-propagating high-temperature synthesis technology,and their thermoelectric properties samples were characterized.Since Co and Ni have one more electron than Fe,the heavily doped samples are all n-typed,and the Seebeck coefficient is improved.And because of the difference in the elemental radius between the Co atom and the Fe atom,the thermal conductivity of the sample is simultaneously optimized.Therefore,the final ZT value of the sample reached a maximum at 50% of Co,which was 0.0225,which was about 200% higher than the intrinsic sample.