Dielectric spectroscopy of lead-free Bi0.5(Na0.75K0.25)0.5TiO3–BiAlO3 ceramics

The electrical properties of (1−x)Bi0.5(Na0.75K0.25)0.5TiO3–xBiAlO3 (BNKT–xBA, x=0–0.100) ceramics were investigated by AC impedance spectroscopy over a wide range of frequency (10−2–105 Hz). X-ray diffraction studies confirmed the formation of a single-phase compound up to x=0.050 and a second phase developed for x=0.075 and 0.100. The diffusive factors, γ, of BNKT–xBA ceramics were found to be in the range 1.66–1.95, which signifies the diffuse phase transition in ceramics. The appearance of a single semicircular arc in the impedance spectrum shows the main contribution of the bulk resistance (Rb) due to grain effects. Rb was found to decrease with increasing temperature, but increase with increasing BiAlO3 (BA) concentration. The conductivity of the ceramics increased with increasing temperature and decreased as BA doping ratios increased. The activation energies obtained from DC conductivity were found to be in the range 0.48–0.65 eV. A typical negative temperature coefficient of resistance (NTCR) behavior like that of semiconductor was observed in the BNKT–xBA ceramics.