The structure and complex impedance spectroscopy of Sr1-xCaxBi4Ti4O15 (x=0, 0.2, 0.4, 0.6, 0.8) ceramics

In the present work, we have synthesized polycrystalline Sr1-xCaxBi4Ti4O15 [x=0, 0.2, 0.4, 0.6, 0.8] ceramics by solid state reactive technique. The analysis indicates that the ceramics present an orthorhombic structure with grains exhibit a plate like morphology. Dielectric relaxations of the above compositions were investigated in the temperature range 100-600 degrees C. Using the Cole Cole plots, an analysis of the dielectric loss with frequency was performed, assuming a distribution of relaxation time. The presence of the peaks in temperature dependent dielectric loss indicates that the hopping of charge carriers is responsible for the relaxation. Impedance studies indicate a non-Debye type relaxation and with increase in temperature relaxation frequency shift to higher side. A notable shift in impedance loss peaks towards higher frequency side explains the conduction in material. The Nyquist curve shows overlapping semicircles, for grain and grain boundary for all the compositions. The frequency dependent AC conductivity at different temperatures indicates that the conduction process is thermally activated process and the spectra follow the universal power law. The conductivity is frequency independent at low temperatures. The variation of DC conductivity confirms that the samples Sr1-xCaxBi4Ti4O15 [x=0: SBT, 0.2: SCBT02, 0.4:SCBT04, 0.6:SCBT06, 0.8:SCBT08] exhibits negative temperature coefficient of resistance behavior at high temperatures. (C) 2015 The Authors. Published by Elsevier Ltd.