Authors: T. Mori, T. Nishimura and Y. Bando
Affilation: National Institute for Materials Science, Japan
Pages: 536 - 539
Keywords: thermoelectric, high temperature, waste heat, microstructure
The search for thermoelectric materials is being carried out with great intensity because of the huge possibilities for useful energy conversion of waste heat. There is obviously a particular need to develop materials which can function at high temperatures. Boron-rich cluster compounds are attractive materials for their stability under high temperature, typically exhibiting melting points of above 2300 K. REB50-type compounds and a homologous series of RE-B-C(N) compounds were synthesized. Seebeck coefficients in excess of 200 V/K are observed at T>1000 K for REB50-type compounds. Strikingly, n-type behavior was observed for RE-B-C(N) compounds which have fewer boron icosahedral layers. Up to now, non-doped B12 icosahedral compounds have all been p-type and this discovery of an n-type compound is important in terms of development of this class of compounds as viable thermoelectric materials. Control of the microstructure was utilized in an attempt to increase the figure of merit of these compounds. Hot press conditions were varied in detail and we find that the change in microstructure improves the high temperature properties whereas the behavior at T<600 K remains unchanged. Substantial increase of the power factor P =  up to a factor of 3 at T=1000 K could be achieved.