Theoretical and experimental study of the phase coexistence and impedance response in multiferroic Gd doped La0.665Bi0.33Ba0.005GdxMn1-xO3 ceramics

Polycrystalline samples of La0.665Bi0.33Ba0.005GdxMn1-xO3 (LBBGMO) (x = 0.25, 0.45, and 0.65) were prepared via using conventional solid–state reaction method. The preliminary structural studies were carried out by X-ray diffraction at room temperature (RT). Rietveld refinement analysis of diffraction data confirmed that for x = 0.25 and 0.45, the structure was orthorhombic but co-existence of orthorhombic and rhombohedral were observed for x = 0.65. The average crystallite size calculated from the W–H plot of all the samples and reported 20.4753 nm, 16.6014 nm, 16.0821 nm for x = 0.25, 0.45 and 0.65 respectively. The dielectric constant for all samples had a negative value at low frequency and positive for higher frequency range. The presence of one semicircle in Nyquist plot were observed, which shows the grain effect in all ceramic materials. At all observed temperatures, the frequency dependence of impedance plots has been utilized to characterize the electrical conduction of the sample which demonstrated the NTCR character (Negative Temperature Coefficient of Resistance). The ac conductivity variation with frequency dependence was well fitted according to Jonscher's power law and ac conductivity increases with increasing temperature.