Metallization And Joining Mechanism Of N-type CoSb₃-based Thermoelectric Materials

CoSb₃ is one of the most promising thermoelectric materials in the middle temperature range?500?-550??,which has excellent mechanical properties and thermal stability.However,the preparation of reliable bonding joint between CoSb₃ and electrode is an indispensable step in the manufacturing process of thermoelectric devices.In addition,due to problems such as the large contact resistance,elemental diffusion,the preparation of reliable diffusion barrier layer on the surface of Skutterudite is also an indispensable step.In this paper,a new method to prepare barrier layer on the surface of Skutterudite and the subsequent bonding method for the n-type skutterudite are proposed.The Co Mo barrier layer was successfully prepared on the surface of Skutterudite by electroplating method.We then joined the metallized CoSb₃ to the Cu Mo electrode by nano silver and diffusion bonding method.In order to solve the problem of element diffusion at the CoSb₃ /Ag/Cu Mo interface,we fabricated a Co Mo barrier layer on the surface of CoSb₃ by electroplating.And after annealing at 450? for 30 min,a metallurgical bonding between Co Mo and CoSb₃ is achieved.The surface morphology of Co Mo layer is affected greatly by the current.when it is 0.09 A,the Co Mo layer has the smallest particle size of 200 nm.The coefficient of thermal expansion of the Co Mo layer was optimized by changing its chemical composition,which can be controlled by the electroplating temperature,current and the concentration of the Mo ions in the solution.The Mo content of Co Mo layer can be controlled between 10 wt.%-50 wt.%.And when the Mo content is between 30 wt.%-40 wt.%,the coefficient of thermal expansion of the Co Mo layer and the n-type Skutterudite is relatively matched.In addition,the growth rate of thickness of Co Mo layer is about 2.5?m/h.After that,nano silver is used to connect the metallized skutterudite to the Cu Mo electrode.There is no crack at the interface and the Co Mo layer effectively suppress the diffusion of Ag and Cu.It is found that when the bonding temperature is 400?,the sintered nano silver is most compact.The strength of the joint is about 15 MPa,and the contact resistance of the joint is only 4.16 ??.cm2.It is found that when the holding time is 30 minutes,the sintered nano silver is most compact.The strength of the joint is up to 15 MPa,and the contact resistance of the joint is only 4.16 ??.cm2.We also joined the metallized CoSb₃ to the Cu Mo electrode by a diffusion bonding method performed at 600°C and 1MPa for 10 min.The Co-Mo/CoSb₃ interface exhibit extremely low contact resistivity of 1.41 ??.cm2,which is the lowest value for the reported thermoelectric modules of any classes of materials.The metallization layer inhibited the elemental inter-diffusion to less than 11 ?m after annealing at 550 °C for 60 hours,indicating a good thermal stability.