Effects of Cr doping in electron-doped manganites La0.9Te0.1MnO3

The effects of Cr doping on Mn sites in the electron-doped manganites La0.9Te0.1MnO3 have been studied by preparing the series La0.9Te0.1Mn1−xCrxO3 (0.05≤x≤0.20). Upon Cr doping, both the Curie temperature TC and magnetization M are suppressed. The resistivity measurements indicate that there exists a weak metal–insulator (M–I) transition for the sample with x=0.05, with an increase in the doping level, the M–I transition disappears and the resistivity increases. Thermopower S(T) exhibits a maximum near TC for all samples. By fitting the S(T) and ρ(T) curves, it is found that the temperature dependences of both S(T) and ρ(T) in the high temperature paramagnetic (PM) region follow the small polaron conduction (SPC) mechanism for all samples. The fitting parameters obtained imply changes of both the average-hopping distance of the polarons and the polaron concentration with Cr doping in our studied samples. In the case of the thermal conductivity κ(T), the variation of κ(T) is analyzed based on the combined effects due to the suppression of the local Mn3+O6 Jahn–Teller (JT) lattice distortion because of the substitution of Cr3+ for Mn3+ ions, which results in the increase in κ, and the introduction of the disorder due to Cr-doping, which contributes to the decrease in κ.