Effect of chromium concentration on the structural, magnetic and electrical properties of praseodymium-calcium manganite

The influence of Cr doping on magnetic, magnetocaloric and electrical properties in a polycrystalline sample of Pr0.7Ca0.3MnO3 is investigated. Structural studies show that our samples are single phase. The magnetization shows that the Pr0.7Ca0.3Mn1-xCrxO3 ceramics exhibit a paramagnetic-ferromagnetic transition with a large magnetic entropy change. The relative cooling power (RCP) values are comparable to those of other manganite. DC conductance G(DC) measurements show that all samples are characterized by a semiconductor behavior. It is found that G(DC) decreases by two decades when increasing chromium concentrations. For the parent compound, dc-conductance is characterized by the appearance of a saturation region at a specific temperature (T-sat = 200 K). For the doped compound, T-sat go beyond room temperature. Conduction mechanism is found to be dominated by the small polaron hopping (SPH) process at high temperature and by variable range hopping one (VRH) at low temperature. AC conductance study confirms that the conductivity is governed by hopping process and obeys to the Jonscher universal power law. The exponent 'n' variation with temperature is in good agreement with Mott theory. Its variation as a function of chromium content indicates that the material turns from metallic to semi-insulating behavior when chromium composition increases. Impedance analysis proves the presence of electrical relaxation phenomenon in the material and confirms that grain boundaries played a main role in the conduction process. (C) 2015 Elsevier B.V. All rights reserved.