Transport behavior of yttrium substituted polycrystalline La_0.7Pb_0.3MnO₃

The transport properties in La_0.7-xY_xPb_0.3MnO₃ (0.0 ≤ x ≤ 0.2) is investigated. The substitution of La³⁺ ions by smaller nonmagnetic Y³⁺ leads to greater spin disorder and induces variations in the magnetotransport behavior. From resistivity versus temperature curves a metal-insulator transition phenomenon is observed at the transition temperature, T_P, decreases as the Y content increases. The resistivity is well fitted using the equation ρ(T) = ρ_nexp[(T^*/T)ⁿ] with n = 1/4 and n = 1/2 at high and intermediate temperatures, respectively. The characteristic temperature T^* varies with Y content in a manner consistent with the localization model of variable range hopping. Below T_P, resistivity varies as a function of power law contributions, ρ = ρ₀ + ρ₂T² + ρ_5/2T^5/2, corresponding to the electron scattering processes in the ferromagnetic phase.