FABRICATION, STRUCTURAL AND AC IMPEDANCE STUDIES OF LAYER-STRUCTURED Bi4Ti3O12 CERAMICS

In the present research bismuth titanate Bi4Ti3O12 (BIT) ceramics was synthesized by the standard solid-state reaction method from the mixture of oxides, followed by free sintering at temperature T=1000 degrees C. BIT ceramics was studied in terms of its chemical composition (EDS), crystalline structure (X-ray), microstructure (SEM) and dielectric properties (ac technique of complex impedance spectroscopy) over a range of frequency (f=100Hz to f=1MHz) and temperature (T=200-500 degrees C). Experimental results confirmed the phase formation. It was found that BIT ceramics crystallized in orthorhombic symmetry, best described with Fmmm space group and the following elementary cell parameters: a=5.409(6)angstrom, b=5.449(2)angstrom and c=32.816(2)angstrom. It was also found that BiT ceramics exhibited the plate like microstructure and stoichiometric chemical composition. Impedance spectroscopy measurements showed contribution of three overlapping relaxation processes (three semicircles in the complex impedance diagrams were observed) ascribed to bulk, grain boundary and electrode/interface polarization phenomena. Impedance data were fitted to the corresponding equivalent circuit using the complex nonlinear least squares (CNLS) method. The ac conductivity for grains, grain boundaries and electrode processes was calculated from CNLS fit of the impedance data and thus the activation energy of ac conductivity (sigma(AC)) and relaxation (tau) was calculated for the three revealed components of the impedance spectra from the slopes of sigma(AC) and tau versus 1000/T plots (semi log scale) in the range of Delta T=200-500 degrees C.