Improving interface properties of Te based thermoelectric materials and composite electrodes

Abstract

Owing to their excellent performances, Te-based thermoelectric materials have been extensively concerned. However little attention has been paid to the bonding interfaces with electrodes, which play an important role in their practical applications. Excessive element mutual diffusion occurs across the bonding interfaces when Te is connected with metallic electrode, such as copper, aluminum, iron, etc, which will impair its transport performance and life especially when they serve in the higher temperature environments. Seeking proper barriers is the key to solving the interface problem. In this work, a gradient bonding structure of Te/FeTe/Fe is prepared in one step by the spark plasma sintering (SPS) method, in which a metallic layer of FeTe, referred to as <i>β</i>(FeTe) phase, is introduced as barrier. The interface microstructure, element distribution, and new phases are analyzed, and the joint properties including contact resistance and shearing strength after being aged are evaluated. The results show that the introduction of <i>β</i>(FeTe) phase can promote the boding of Fe/<i>β</i>(FeTe)/Te and thus inhibiting the excessive element diffusion across the interfaces, which is due to the formation of <i>ε</i>(FeTe₂) phase between <i>β</i>(FeTe) phase and Te. The contact resistance of Fe/<i>β</i>(FeTe) and <i>β</i>(FeTe)/Te are 4.1 μΩ·cm² and 7.54 μΩ·cm², respectively, and the shearing strength are 16.11 MPa and 15.63 MPa, respectively. The annealing temperature has significant effect on the performance of the gradient bonding structure. It has been indicated that the whole joint still owns good performance after being annealed at 553 K for 15 days, while it decreases sharply when the temperature is increased to 573 K. Hence, the optimal service temperature of Te/<i>β</i>(FeTe)/Fe should not be higher than 553 K. The gradient bonding structure is successfully achieved, thus attaining the purposes of inhibiting interface elements from excessively diffuse, reducing interface residual stress, and improving interface working stability and service life. So the design ideas and research results in this work have great reference significance for the study on semiconductor devices.