Effect of rare-earth substitution at La-site on structural, electrical and thermoelectric properties of La^sub 0.7-x^RE^sub x^Sr^sub 0.3^MnO^sub 3^ compounds (x?=?0, 0.2, 0.3; RE?=?Eu, Gd, Y)

In the present communication, we present results on the effect of rare-earth (RE) substitution at La-site on the structural, electrical and thermoelectric properties of La0.7−xRExSr0.3MnO3 compounds. The lattice parameters are observed to decrease with RE-doping which is attributed to the fact that the substituted RE ions (RE = Eu, Gd and Y) are smaller than that of La ion. In high temperature semiconducting regime, small polaron hopping (SPH) model is valid, whereas, variable hopping model is valid in low temperature metallic region. The resistivity in the entire temperature range follows percolation model. All the samples exhibit sign reversal in thermopower, S. From temperature dependent S data, it is seen that SPH model is applicable in high temperature regime.