Flash combustion synthesis of electron doped-CaMnO3 thermoelectric oxides

Nano-crystalline particles of calcium manganite Ca-1 (-) xRxMnO3 (R = Yb, Dy, Sm and Bi, with x = 0.0 and 0.1), having a complex orthorhombic-perovskite structure, have been successfully synthesized by flash combustion method. The powders obtained were thoroughly characterized by scanning electron microscopy and thermal analyses. The average crystallite size is found in the range between 100 and 200 nm. The crystallization was followed by in situ high-temperature X-ray diffraction in air. The XRD analyses show that the cell volume of the orthorhombic-perovskite structure for Ca0.9R0.1MnO3 increased with a rise in the ionic radius of the R3+ cations. The stoichiometry of the samples was confirmed by energy dispersive spectroscopy analysis. The temperature dependence of thermoelectric properties was measured from 75 to 400 degrees C and the R-dopant effects were investigated. The electrical resistivity is strongly dependent on the nature of the substituent ions. All the samples exhibit negative values of the thermopower, which indicates that the electrons are the predominant charge carriers (n-type conduction). Finally, the highest power factor of 165 mu W.m(-1) K-2 has been obtained at 400 degrees C for Ca0.9Yb0.1MnO3. In this paper, we suggest to use the fine grains of Ca0.9R0.1MnO3 as promising candidates for thermoelectric applications. (C) 2014 Elsevier B.V. All rights reserved.