Influence of Te doping on the perovskite manganite La0.5Ca0.5MnO3

Systematic studies of resistivity ρ, thermoelectric power (TEP) S, and thermal conductivity κ have been performed on the perovskite manganite La0.5Ca0.5−xTexMnO3 (0≤x≤0.10). For the sample with x=0, S(T) exhibits a semiconducting behavior over the whole temperature range. However, for x>0 samples, an obvious peak in S(T) curves is observed. It is found that the temperature dependence of both in S(T) and ρ(T) in the high-temperature paramagnetic (PM) region follows the small polaron transport mechanism for all the samples. In the low-temperature insulating region, variable-range-hopping (VRH) model matches the experimental data better. But in the intermediate-temperature ferromagnetic (FM) region below Curie temperature TC, ρ(T) and S(T) of the samples with x>0 are well fitted by the formula: ρ = ρ 0 + ρ 2 T 2 + ρ 4.5 T 4.5 and S = S 0 + S 3 / 2 T 3 / 2 + S 4 T 4 , respectively, implying the importance of electron–magnon scattering. As to thermal conduction κ(T), the low-temperature peak is suppressed due to Te-doping. The decrease of κ with increasing Te-doping is suggested to come from the combined effect of the scattering of the Mn3+O6 Jahn–Teller (JT) distortion and the disorder to the phonon and enhanced phonon drag effect.