Optimizationthe Properties Of ZrNiSn Half-heusler Alloy Thermoelectric Materials By Multielement And Multisite Doping

As a functional material that can convert thermal energy and electrical energy directly,thermoelectric materials have been regarded as a new material with broad application prospects since its discovery.Today,with the increasing energy crisis,research on thermoelectric materials has become more practical,especially in the areas of waste heat,waste heat power generation and replacing traditional refrigeration equipment.Thermoelectric materials utilize the Seebeck effect and the Peltier effect to achieve both power generation and cooling functions.In this paper,medium temperature ZrNiS n based half-Heusler alloy thermoelectric materials are selected as research objects.The suspension alloy is combined with a long time high temperature annealing to obtain a desired alloy sample with a spark plasma sintering process.Multielement and multisite-doping strategies optimize the thermoelectric properties of the material and reduce the cost of material preparation.The following main conclusions are drawn:1.Study on the influence of P-type doping?Sc?,isoelectronic doping?Ti,Hf?and N-type doping?V,Nb and Ta?on the thermoelectric properties of materials by Zr sites:P-type doping Miscellaneous,the semiconductor properties of the material change from N-type to P-type,which will greatly damage the thermoelectric properties of the materia l.The isoelectronic doping is beneficial to reduce the lattice thermal conductivity of the material due to the introduced massand stress fluctuation.The thermoelectric properties of the material are improved due to the N-type doping significantly increases the carrier concentration of the material,improves the electrical conductivity of the material,which also plays an important role in suppressing the thermal conductivity of the lattice.The approximate effect of each doping element on the thermoelectric parameters of the material is as follows:Conductivity:Sc<Hf<Ti<Zr<V<Ta<Nb,power factor:Sc<Ti<Zr<V<Hf<Nb<Ta,lattice thermal conductivity:Sc<Zr<Ti<Hf<Ta<V<Nb.2.The multi-element M(Ti_0.25Hf_0.25V_0.25Nb_0.25)doping in the Zr position improves the thermal conductivity of the material while improving the thermal conductivity of the material and optimizing the thermal conductivity of the material finally.It is mainly due to the decrease in the lattice thermal conductivity of the material caused by the introduction of mass fluctuations and stress fluctuations?point defects?,when the optimal doping amount of the N-type doping element to the material is 5%,the power factor of the sample reached 4180?W/m/K,ZT value reached 0.76.3.Sb partial replacement of Sn introduces additional carriers?electrons?,which increases the conductivity of the material.When the introduction amount is 1%,the material's power factor is optimized to 4760?W/m/K²;The Sb ionic radius is larger than the ionic radius of Sn.Therefore,the doping also brings additional lattice defects and local distortion of the crystal lattice,which is beneficial to lower the lattice thermal conductivity and the ZT value of the material,is further increased to 0.84.4.The energy filtering effect is introduced by the Full-Heusler alloy phase formed by self-doping of the Ni site,so that low-energy carriers are scattered,the Seebeck coefficient of the material is increased,the thermoelectric properties of the material are optimized,and the phonon scattering is simultaneously performed.Reinforcement,the lattice thermal conductivity of the material is suppressed;combined with the ball milling process to obtain finer grains,the additional grain boundary scattering after grain refinement further reduces the lattice thermal conductivity of the material to 0.99 W/m/K,the material achieved an optimum ZT value of about 1.2 finally.In addition,under the premise of achieving the same high performance,the amount of Hf element used in this paper is lower than that reported in most literature reports,which directly reduce the preparation cost of the material.