Enhancement of the thermoelectric figure of merit in M ∕ T ∕ M ( M = Cu or Ni and T = Bi 0.88 Sb 0.12 ) composite materials

The resultant thermoelectric figure of merit Z T of M ∕ T ∕ M ( M = Cu or Ni and T = Bi 0.88 Sb 0.12 ) composite materials welded with Bi-Sb alloy was measured at 298 K as a function of relative thickness of Bi-Sb alloy and compared with Z T values calculated by treating it as an electrical and thermal circuit. It was first clarified experimentally that the observed Z T values of composite materials have a local maximum at an optimum volume fraction (corresponding to the thickness) of Bi-Sb alloy in spite of macroscopic composite materials, owing to a significant enhancement in the Seebeck coefficient. It is sure that the enhancement in α is caused by the boundary Seebeck coefficient generated at the interface between Bi-Sb alloy and a metal. It was thus clarified that the interface effect appears clearly in macroscopic systems. The observed maximum Z T values at 298 K reached a surprisingly great value of 0.44 at a relative thickness of approximately 0.7, which corresponds to approximately 1.7 times as large as 0.26 of Bi 0.88 Sb 0.12 alloy and to about half of 0.8-0.9 of commercially utilized bismuth telluride compounds. So enhanced Z T may not be utilizable for a Peltier module, but is available for generators.