Sodium deficiency effect on the transport properties of La0.8Na0.2−x□xMnO3 manganites

Effect of sodium deficiency on the transport properties of La0.8Na0.2−x□xMnO3 manganites is investigated using impedance spectroscopy technique. In the whole explored temperature range (77-700 K), conductivity measurements show the appearance of a metal-semiconductor transition for all investigated samples. Also, a saturation region is observed in σ (T) curves. It is found that conduction mechanism is governed by hopping process. The conductivity of the material decreases with increasing sodium deficiency. The transition temperature and the activation energy values inferred from grain boundary resistance and conductivity analysis are closed to each other. Such result confirms the contribution of grain boundary on the electrical conductivity. The variation of the Average Normalized Change (ANC) and its derivative with temperature gives important information about the available density of trapped charge states. The obtained results explain the observed saturation region in conductivity at high temperature region.