Effects of Cr doping in electron-doped manganites La_(0.9)Te_(0.1)MnO_3

摘要

The effects of Cr doping on Mn sites in the electron-doped manganites La_(0.9)Te_(0.1)MnO_3 have been studied by preparing the series La_(0.9)Te_(0.1)Mn_(1-x)Cr_xO_3 (0.05 ≤ x ≤ 0.20). Upon Cr doping, both the Curie temperature T_C 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 T_C 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 Mn~(3+)O_6 Jahn-Teller (JT) lattice distortion because of the substitution of Cr~(3+) for Mn~(3+) 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.