Structural, dielectric and impedance response of BCT reinforcement on BZT matrix

Lead-Free composites of (1-x)BaZr0.2Ti0.8O3-(x)Ba0.7Ca0.3TiO3 (BZT-BCT) were prepared using ferroelectric BaZr0.2Ti0.8O3 and Ba0.7Ca0.3TiO3 by solid-state reaction method with different mole fractions of x (x = 0.15, 0.30 and 0.45). The preliminary structural studies were carried out by X-ray diffraction at room temperature (RT). It revealed that the samples had both tetragonal and orthorhombic structures at room temperature. Rietveld refinement analysis of diffraction data confirmed the coexistence of the tetragonal and orthorhombic phases in the sintered samples. The average crystallite size calculated from the W-H plot of all the samples varies between 0.0416 and 0.0293 mu m. The dielectric and impedance relaxation properties of the (1-x)BaZr0.20Ti0.80O3-(x)Ba0.70Ca0.30-TiO3 ceramics were analysed from RT-600 degrees C in the frequency range of 100 Hz-1 MHz. The ac conductivity variation with frequency dependence was well fitted according to Jonscher's power law. While the diffusion factor increases from 1.21 to 1.30 with increase in x from 0.15 to 0.45, indicating a composition-induced diffuse transition. The presence of two semicircles in Nyquist plot were observed, which shows the grain and grain boundary contribution in all samples. The existence of a non-Debye type of relaxation behaviour of the samples was also confirmed from impedance analysis as the centre of the semicircles lies below the real axis. At various 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).