Off-diagonal thermoelectric effect in tilted layered materials

Off-diagonal thermoelectric effect is an unconventional thermoelectric phenomenon which emerges in layered materials with tilted alignment. Here, we report development of unique functionalities using the off-diagonal thermoelectric effect in two different material systems; (i) tilted-oriented thin films of layered cobaltite Ca_xCoO₂, and (ii) artificial tilted multilayer of Bi/Cu and Bi_0.5Sb_1.5Te₃/Ni. Ca_xCoO₂ thin films enabled generation of an extremely large film in-plane voltage of 1 V by introducing a unit temperature difference in the film out-of-plane. On the other hand, Bi/Cu multilayer showed enhanced power factor of 50.1 μW/cmK², which was ~1.5 times larger than that of the constituent Bi alone. We also realized high electrical power generation of 1.3 W in the Bi_0.5Sb_1.5Te₃/Ni multilayer fabricated in a tubular structure. These features provide potential applications to sensitive optical/thermal sensors and high-power thermoelectric generators.