La3-xTe4 thermoelectric legs with interlocking electrode interface via ink extrusion printing and sintering of powders

Geometrically-complex thermoelectric legs of n-type LaTe1.47 with relative densities of ~82% and high phase purity are synthesized via ink-extrusion printing of pre-alloyed powders at ambient temperature, followed by debinding and sintering at high temperature. By using Te-rich powder, we offset Te sublimation during sintering to achieve LaTe1.47 legs with a high figure of merit value (zT = 1.49 ± 0.24 at 1250 K), on par with state-of-the-art LaTe1.46 synthesized via hot pressing. Also, the ink printing methodology enables printing and diffusion bonding between a LaTe1.47 leg and a Ni electrode with a non-flat interface designed to achieve mechanical interlocking with minimal interdiffusion. To simulate the thermomechanical stress at interlocking interfaces – from cooling following fabrication to heating to operation – we develop a finite-element model of the leg/electrode assemblies and demonstrate the importance of creep in relaxing the stress state of both phases, using creep properties measured on dense La3-xTe4 at 900-1000ºC. Additionally, these designed interfaces have the potential to mitigate crack propagation at the thermoelectric-metal junction caused by thermal expansion mismatch. The ink printing approach presented here enables scalable, cost-effective fabrication of high-performing La3-xTe4 thermoelectric legs which are conducive to designed electrode-leg interface bonding, towards efficient and thermomechanically-robust high-temperature thermoelectric devices.