Possibility of controlling the conduction mechanism by choosing a specific doping element in a praseodymium manganite system

Abstract

Electrical properties of Pr_0.7Ca_0.3Mn_0.9X_0.1O₃ (X = Co, Ni, Cr and Fe) systems have been investigated using impedance spectroscopy measurements. The reported results confirmed the role of cationic disorder on the transport properties of the doped Pr_0.7Ca_0.3MnO₃ system. For the case of the substitution by Co and Ni and Fe transition metals, the lower temperature side has been marked by the activation of the hopping conductivity over the nearest sites. Moreover, the Shklovskii–Efros-variable range hopping conductivity mechanism has been observed in the case of the substitution by Cr element. In the high temperature range, the evolution of the resistance with temperature confirmed the activation of a hopping process. In such a temperature range, the conduction process of all the studied compounds is dominated by a thermally activated small polaron hopping mechanism. For the Pr_0.7Ca_0.3Mn_0.9Cr_0.1O₃ compound, AC studies have confirmed that the electrical conductance should be investigated in terms of an activated quantum mechanical tunneling process. At higher frequencies, the Pr_0.7Ca_0.3Mn_0.9Fe_0.1O₃ compound is characterized by the existence of a high frequency plateau. For the Pr_0.7Ca_0.3Mn_0.9Fe_0.1O₃ ceramic, the dispersive region of the spectrum has confirmed the activation of the correlated barrier hopping mechanism. Thus, the conductance is found to follow the double Jonscher power law only for the temperature range of [80 K, 200 K]. For the Pr_0.7Ca_0.3Mn_0.9Ni_0.1O₃ compound, the evolution of the frequency exponent has confirmed the activation of two conduction mechanisms. The non small polaron tunneling mechanism was activated at lower temperatures. Accordingly, the activation of the correlated barrier hopping mechanism was detected for the high temperature range. For Pr_0.7Ca_0.3Mn_0.9Co_0.1O₃ manganite, the coexistence of two conduction mechanisms (correlated barrier hopping and the non small polaron tunneling) is noticed. The latter's were activated in the whole of the explored temperature range. Using the scaling model, the spectra of both Pr_0.7Ca_0.3Mn_0.9Cr_0.1O₃ and Pr_0.7Ca_0.3Mn_0.9Ni_0.1O₃ compounds merge into a single master curve, which confirms the validity of the time temperature superposition principle.