Effects of Cr doping in electron-doped manganites La 0.9Te 0.1MnO 3

Abstract

The effects of Cr doping on Mn sites in the electron-doped manganites La 0.9Te 0.1MnO 3 have been studied by preparing the series La 0.9Te 0.1Mn 1− x Cr x O 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 .