1997 Volume 9 Issue 3-4 Pages 171-176
A new class of thermoelectric materials, skutterudites and filled skutterudites, has become a topic because the materials have a dimensionless thermoelectric figure of merit ZT of 1 at 800K. Skutterudites are binary semiconducting compounds with the general formula MX3 (where M is Co, Rh, Ir; and X is P, As Sb). Within these materials, the three isothermal antimonides such as IrSb3, RhSb3, and CoSb3 exhibit excellent electronic transport properties, including a high value of the hole mobility (8000cm2/Vs). For example, p-type CoSb3 has a hole mobility value of 3000cm2/Vs at room temperature, and ZT of Pd/Pt-doped CoSb3 is 0.85.
Filled skutterudite alloys with the general formula of RM′4X12, where R is La, Ce, Pr, Nd or Eu and M′ is Fe, Ru or Os, are particularly interesting, because formally they are isoelectric (that is, have the same number of valence electrons per unit cell) with the binary skutterudites such as CoSb3. Relative to CoSb3, the filled skutterudites exhibit a remarkable factor-of-ten decrease in the lattice thermal conductivity, which reaches a value at room temperature equal to that of vitreous silica (SiO2). This is believed to be due to the “rattling” effect of the rare earth atoms that scatters the heat-carrying phonons. For example, CeFe3CoSb12 or LaFe3CoSb12 has a low lattice thermal conductivity value of about 0.015W/cmK at near room temperature.
