Microstructural evolution of the interfacial layer in the Ti-Al/Yb0.6Co4Sb12 thermoelectric joints at high temperature

A thermoelectric (TE) device is basically fabricated by joining p- and n-type thermoelectric materials with electrodes. For skutterudite (SKD) based TE devices, Ti and alloys like Co-Fe-Ni are widely used as the barrier layer joining the SKD and the electrode. In this paper, TE joints composed of Yb0.6Co4Sb12 (Yb-SKD) and a Ti-Al barrier layer with various Al contents (0-15 at.%) were fabricated by a one-step SPS process. The influence of the Al content on the evolution of the interfacial microstructure during accelerated aging at 600 degrees C was studied. During sintering and aging, Ti and Al diffused into each other and formed inert Ti-Al alloys, which hindered the interfacial diffusion and resulted in a lower growth rate of the diffusion layers. On the other hand, excess Al at the Ti-Al/Yb-SKD interface encouraged the interfacial diffusion. The interplay of the above two mechanisms decides the inter-diffusion behaviors at the interface. In this work, the two mechanisms reached balanced when the Al content was 6 at.%, which resulted in the best interfacial stability and the highest shear strength after aging. At the same time, with the increase of the Al content in the Ti-Al barrier layer, the CTE mismatch between the Yb-SKD and the Ti-Al barrier layer was reduced, consequently the interfacial integrity after aging was improved. As a result, the contact resistivity of the Ti-Al/Yb-SKD joints (Al: 6-12 at.%) remained below 12 mu Omega cm(2) after 16 days of aging. (C) 2014 Elsevier B.V. All rights reserved.