Effect of doping of alkaline metal ions on structural and electrical properties of Bi0.8M0.2FeO3-modified Na0.5Bi0.5TiO3 ceramics (M=Ca, Sr, and Ba)

In the present work the electrical properties of polycrystalline 0.9(Na0.5Bi0.5TiO3)-0.1(BiFeO3) and Bi0.8M0.2FeO3-modified Na0.5Bi0.5TiO3, (where M = Ca, Sr, and Ba) lead-free ceramics were investigated through impedance spectroscopy. X-ray diffraction analyses indicate the incorporation of alkaline earth metal ions at A-site of perovskite type ceramics revealing the conservation of crystal structure (rhombohedral structure with R3c space group) in the synthesized compositions. The substitution of alkaline earth metal ions at the A-site in perovskite-structured ceramics led to an enlargement of unit cell. The appearance of depressed semicircle arcs in Nyquist plots suggests non-Debye nature of relaxation occurring in studied samples. An equivalent circuit model comprising of parallel combination of resistance and constant phase element was used for the simulation of Nyquist plots. The mismatching of peaks in the combined spectroscopic plots of Z″ and M″ versus frequency also confirms the occurrence of non-Debye relaxation in BBFO sample. The ac conductivity studies show that the conduction mechanism changes from correlated barrier hopping model (CBH) to overlapping large polaron tunneling, when alkaline metal ions are substituted in place of Bi3+ ions. Activation energy values calculated from conductivity data suggest the presence of oxygen vacancies. The dielectric, impedance and conductivity behaviors are significantly influenced by the distortion of Ti/FeO6 octahedron.