One dimensional compounds with large thermoelectric power:: Ca3Co2O6 and Ca3CoMO6 with M = Ir4+ and Rh4+

In the Ca-Co-O system. there exists at least two identified phases, Ca3Co4O9 and Ca3Co2O6 exhibiting 2D CoO2 planes and 1D Co-Co chains, respectively. Both oxides are characterized by large thermopower values at room temperature, the largest value being obtained for Ca3Co2O6 (Seebeck coefficient, S-300K = 450 muV K-1). However, the electrical resistivity of the latter is too large (typically 50 Omega cm) for applications as thermopower materials. Interestingly, the substitutions of Ir4+ or Rh4+ for one cobalt out of two in the chain do not greatly affect the electronic properties in contrast to the substitution by Sc3+ (3d(0)). This emphasizes that the Ir or Rh cations can play a similar role to that of the Co cations. This opens a new route for the search of new thermoelectric materials alternative to the cobaltites. (C) 2003 Elsevier B.V. All rights reserved.