Extrusion-printed La_3-xTe₄ legs with interlocking Ni electrode for high-temperature thermoelectric devices.

Abstract

Thermoelectric materials, despite their desirable heat-to-electricity conversion properties, have seen limited commercial viability due to their labor-intensive and high-cost conventional synthesis and assembly processes. Here, we demonstrate an ink printing/sintering approach which unlocks cost-effective fabrication of high-performing, geometrically-complex La_3-xTe₄ thermoelectric legs with high relative densities and phase purity. LaTe_1.47 legs are created by ink-extrusion printing of pre-alloyed powders, followed by debinding and sintering at high temperature; they achieve a high figure of merit (zT = 1.49 ± 0.24 at 1250 K), on par with state-of-the-art LaTe_1.46 synthesized via traditional hot pressing. Furthermore, the ink printing methodology enables printing and diffusion bonding of non-flat interfaces between a LaTe_1.47 leg and a Ni electrode, which are designed to achieve high mechanical interlocking with minimal chemical interdiffusion. After measuring creep properties on dense La_3-xTe₄, we perform simulations of the thermomechanical stress at these LaTe_1.47/Ni interlocking interfaces during operation; this demonstrates the importance of creep in relaxing the stress state of both phases and the potential for designed interfaces to mitigate crack propagation at the thermoelectric-metal junction. This additive approach addresses the key challenges with thermoelectric device fabrication, enabling thermoelectric devices which are economical, scalable and thermomechanically-robust at very high temperatures.