Enhancement of the thermoelectric performances of In2O3 by the coupled substitution of M2+/Sn4+ for In3+

The thermoelectric properties of air-prepared cosubstituted indium oxide based compounds belonging to the series In(2-2x)M(x)Sn(x)O(3) (M=Zn, Cu, or Ni) have been studied. X-ray diffraction studies show that the solubility limit x(max) increases from x(max)=0.35 for M=Cu to x(max)=0.45 for M=Zn and x(max)=0.55 for M=Ni. The lattice parameters, following the Vegard law with increasing substitution rates are in good agreement with the divalent oxidation state for the M cations. Compared to the undoped In(2)O(3) prepared in air, the electrical resistivity of the cosubstituted phases (M=Zn,Cu) is strongly decreased and exhibits a metallic behavior. A more complex behavior is observed for the Ni/Sn cosubstituted samples whose resistivity first decreases and then increases with x. The lowest resistivity values do not exceed 0.5 m Omega cm at room temperature. Despite the lower values of the thermopower in cosubstituted samples, the thermoelectric power factor is significantly higher than that of the undoped In2O3, leading to values exceeding 5.10(-4) W m(-1) K(-2). Furthermore, as the lattice thermal conductivity is strongly reduced by the cosubstitution due to mass fluctuation scattering of the phonons, promising thermoelectric figure of merit ZT is observed, close to 0.3 at 1273 K in In(1.6)Zn(0.2)Sn(0.2)O(3). Thus, this study emphasizes the important role of cosubstitution to improve the thermoelectric properties of these n-type oxides. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2986148]