Effect of Fe - substitution on phase transformation, optical, electrical and dielectrical properties of BaTiO3 nanoceramics synthesized by sol-gel auto combustion method

The structural, microstructural, optical, electrical and dielectrical properties of nanocrystalline Fe substituted BaTiO3 synthesized by sol-gel auto combustion have been investigated. The X-ray diffraction (XRD) analysis revealed the existence of the tetragonal phase for lower Fe content (x = 0.0-0.3) whereas, coexistence of the tetragonal and hexagonal structure of higher Fe content (x = 0.4 and 0.5). The lattice constant (a and c) and unit cell volume (V) increases with increase in Fe content; and an average crystallite size (t) was recorded in the range of similar to 14-20 nm. The surface morphology as examined using field emission scanning electron microscopy (FESEM) and the compositional stoichiometry was confirmed by energy dispersive spectrum (EDS) analysis. The UV-Vis spectra showed that the band gap energy sensitively depends on the Fe concentration x. DC-electrical conductivity (sigma) was recorded in the temperature range of 333-714 K which was found to be increases with increasing temperature and Fe concentration; indicating that an electrical conduction was a thermally activated process. The type of temperature dependent DC conductivity indicates that the electrical conduction in the material is a thermally activated process. The dependencies of the conductivity contributions were predicted from the simple defect model presented, in which oxygen vacancies charge compensate Fe substitution of Ti. Dielectrical property was measured as a function of frequency in the range 50 Hz - 5 MHz at room temperature which was found to be higher at lower frequencies. Dielectric constant (epsilon') and loss tangent (tan delta) shows strong compositional as well as frequency dependences.