Study On Improving The Combination Properties Of Te Based Thermoelectric Joints

Thermoelectric material is a new type of energy material which can realize the mutual conversion between heat energy and electric energy through carrier motion.The integrated device has the advantages of small volume,light weight and simple structure.In the process of device service,the performance of the interface between thermoelectric material and electrode is the key to determine the conversion efficiency of the device.Therefore,in the process of device development,the research on the interface behavior of thermoelectric joint is as important as the performance of thermoelectric material.Solving the problems in the process of improving the interface performance is of great significance for the application of thermoelectric devices.Owing to its special quasi one dimensional band nesting structure and relatively complex crystal structure,Te has become a potential thermoelectric material.However,the research on Te based thermoelectric joint has been rarely reported.In this paper,Te based thermoelectric joint was taken as the research object.The carrier concentration in the material was improved by doping element Sb in Te,and then the performance of thermoelectric material was optimized.Meanwhile,Fe Te compound and metal Ni were introduced as barrier layer in the process of interface structure design.The joints Te/Fe Te/Fe,Te_0.985Sb_0.015/Ni/Al and Te_0.985Sb_0.015/Ni/Cu with optimized properties were successfully prepared.The purpose of this paper is to solve the problem of excessive mutual diffusion of interface elements and improve the service stability of thermoelectric devices from the perspective of interface structure design.It is considered that the introduction of a suitable barrier layer between thermoelectric materials and electrode materials can effectively inhibit the diffusion of interface elements and form a stable interface between materials.For material optimization,the electrical properties of Te based thermoelectric materials were obviously improved after doping with Sb.The sample Te_0.985Sb_0.015showed the optimal power factor,which can reach 15μWK^-2cm^-1 around 500K.For research on thermoelectric joint,in the early stage of the experiment,the Te/Fe joint prepared by SPS method showed the problems of serious interdiffusion of interface elements and structural defects.Fe Te prepared by mechanical alloying method as a barrier layer was introduced into the interface.The prepared gradient bonding structure showed a high quality bonding interface and a stable Fe Te₂ reaction layer was formed at the Te/Fe Te interface.After 15 days of annealing,the contact resistance of the two interfaces is about 45μΩ·cm² and the shear strength is above 10MPa,which meets the application requirements of the joint.In order to solve the interface problems of Te/Al joint,Ni was used as the barrier layer.The Te_0.985Sb_0.015/Ni/Al joint appeared structure quality with high quality and uniform composition distribution.However,after annealing at 573K,Al Ni₃ was enriched at the interface of Al/Ni and diffused to Al matrix in the way of corroding grain boundary,causing serious weakness to the joint structure performance.When the Al electrode in the joint was replaced by Cu,the interface microstructure showed excellent thermal stability.The interface properties of Te_0.985Sb_0.015/Ni/Al and Te_0.985Sb_0.015/Ni/Cu joints before and after annealing were compared.Before annealing,the interfacial shear strength of Te_0.985Sb_0.015/Ni/Al joint is slightly higher than that of Te_0.985Sb_0.015/Ni/Cu joint because of the sufficient element diffusion at the interface.With the extension of annealing time,the grain boundary defects appeared in the Al matrix and the mechanical properties of the joint decreased significantly.The interfacial shear strength of Te_0.985Sb_0.015/Ni/Cu was maintained at about 16MPa because of the element diffusion on both sides of the Cu/Ni interface was gradually sufficient with annealing time.The interface contact resistance of the two kinds of joints kept about 15μΩ·cm² after annealing for 30 days,which is only twice as large as that before annealing.The conversion efficiency and output power of joints were tested in the study.The results showed that Te_0.985Sb_0.015/Ni/Cu had better stability and the conversion efficiency of Te_0.985Sb_0.015/Ni/Cu could reach about 0.4%when the temperature difference is around 170K.