Unified DC-AC transport analysis of few Ni-substituted Pr_0.7Ca_0.3MnO₃: from polaron dynamics to time-temperature superposition principle

The influence of low nickel substitution on the structural and electrical properties of the Pr_0.7Ca_0.3Mn_0.98Ni_0.02O₃ manganite compound has been investigated. The novelty of this work lies in demonstrating that even a very low Ni substitution level is sufficient to tune the charge transport behavior while preserving the single-phase orthorhombic Pnma structure, as confirmed by room-temperature X-ray diffraction analysis. DC resistance measurements reveal semiconducting behavior over the entire investigated temperature range. The electrical transport mechanism evolves with temperature, being governed by the Small Polaron Hopping (SPH) model at high temperatures, the Shklovskii–Efros Variable Range Hopping (SE-VRH) model at intermediate temperatures, and the Mott Variable Range Hopping (Mott-VRH) mechanism at low temperatures. The frequency-dependent conductance spectra are successfully interpreted using the double Jonscher power law, the single Jonscher power law, and the Drude model, highlighting the coexistence of hopping and tunneling conduction processes. The temperature dependence of the derivative of the Average Normalized Change (ANC) parameter reveals the presence of multiple trapping centers. The first and second ANC levels are activated at the first activation temperature (T_ANC1) and the second activation temperature (T_ANC2), respectively, corresponding to transitions between different conduction regimes. In addition, the decrease in the blocking factor with increasing temperature indicates improved charge carrier mobility. The time–temperature superposition principle (TTSP) is validated using the scaling approach; however, a deviation from Summerfield scaling is observed at high frequencies. These findings provide deeper insight into the role of low Ni substitution in controlling the structural stability and charge transport mechanisms of manganite systems, highlighting their potential for future electronic and energy-related applications.