Structural, electrical and dielectric properties of Bi-doped Pr0.8-xBixSr0.2MnO3 manganite oxides prepared by sol-gel process

Abstract

The aim of this paper is to investigate the structural, electrical and dielectric properties of Pr0.8-xBixSr0.2MnO3 (x = 0, 0.05 and 0.1) perovskite materials. Our samples were synthesized by sol-gel route and characterized by X-ray powder diffraction at room temperature. It has been demonstrated that they crystallize in the orthorhombic perovskite system with Pnma space group. As x varies from 0 to 0.1, the MnO bond length and the unit cell volume increases. Consequently, the bandwidth describing the overlap between the Mn3d and O2p orbital is reduced and this affects physical properties. The studied samples were also characterized by complex impedance spectroscopy in a wide range of temperature and frequency. DC conductance results show that doping by Bi suppresses the metal behavior observed at low temperatures in the parent compound. The conductivity decreases when increasing the concentration of Bi due to the reduction of the specific free volume. AC conductivity measurements were split in two parts: The metallic region is well described by the classical Drude model and the semiconductor one was well fitted by the universal Jonscher power law. Results show that the conduction mechanism is described by non-overlapping small polaron tunneling (NSPT) model. Besides, the Cole-Cole plots which are fitted by adequate equivalent circuits show the contributions of grain and grain boundaries in the conduction mechanism. At high temperatures, the total conductivity tends to be governed by grains. Dielectric results show that the Pr0.75Bi0.05Sr0.2MnO3 sample has better dielectric properties than Pr0.7Bi0.1Sr0.2MnO3. Dielectric loss is analyzed by Giuntini theory and correlated with conduction losses. The energy required for carriers to jump over the potential barriers is determined.