Charge transport mechanism and percolation model in La_0.75Ca_0.25−xNa_xMnO₃ (0 ≤ x ≤ 0.10) manganites

In this communication, La_0.75Ca_0.25−xNa_xMnO₃ (0 ≤ x ≤ 0.10) samples were synthesized by the Flux method and their structural and electrical properties were systematically undertaken. X-ray diffraction of the samples showed an orthorhombic structure with a Pbnm space group. Furthermore, to get a better understanding of the electrical properties, the resistivity ρ(T) as a function of temperature was measured by a standard four-probe method. The maximum resistivity values decreased and the insulator–metal transition temperature (T_M–SC) increased with increasing magnetic field. At low-temperature region (T < T_M–SC), ρ (T) was fitted by the equation ρ (T) = ρ₀ + ρ₂T² + ρ_4.5T^4.5, which indicates that the transport mechanism is governed by a combination of electron–electron, electron–magnon, and electron–phonon scattering processes. Also, at the high-temperature (T > T_M–SC) region, the transport mechanism was explained using the adiabatic small polaron hopping and the variable-range hopping models. Then, to get insights into the change in the resistivity plots, in entire temperature, ρ(T) was fitted by the percolation model. Interestingly, it is important to note that the activation energy (Ea) decreased with increasing Na⁺ content, which indicates the enhancement of the double-exchange (DE) interaction. Moreover the magnetoresistance (MR %) effect was studied.