One-step bonding of Ni electrode to n-type PbTe - A step towards fabrication of thermoelectric generators

PbTe-based thermoelectric materials are good candidates for harvesting waste heat at mid-range temperatures due to their high thermoelectric efficiencies. Excellent quality and reliability of the bonding between the thermoelectric material and the electrode at high temperatures are essential for manufacturing thermoelectric generators. Here, a technique has been developed to achieve high-quality bonding between PbTe and the electrode. We have successfully performed one-step sintering of nickel electrode to n-type PbTe powder using spark plasma sintering. The fabricated interphase, composed of nickel telluride, is continuous and homogeneous across the junction, without visible flaws on the electrode or in the interphase and PbTe. To evaluate the long-term thermal stability of the fabricated bond, an aging test was conducted at 823 K for 360 h under vacuum. The microstructures and chemical composition of the fabricated bonding and the aged sample were investigated in detail by scanning electron microscopy equipped with energy dispersive X-ray spectroscopy analysis. No excess reaction was observed between the electrode and the thermoelectric material after aging, supporting the formation of a chemically stable interphase, which acts as a diffusion barrier. Degradation of the PbTe was detected after aging, however. The fabricated interface meets the required criteria for maximum efficiency of PbTe materials.