Influence of NaNbO3 on the structural, optical and dielectric properties of 0.05(K0.5Bi0.5TiO3)-0.95(NaNbO3) composites ceramics

A new polycrystalline lead-free 0.05(K0.5Bi0.5TiO3)-0.95(NaNbO3) (KBT-NN) composites ceramics have been prepared by solid-state reaction method and their structural, optical, dielectric, ferroelectric and impedance properties are investigated. X-ray diffraction and Rietveld refinement data reveal that this composites ceramics possesses a perovskite-type orthorhombic structure after the diffusion of K0.5Bi0.5TiO3 into the NaNbO3. An appreciable change in its vibrational phonon modes of KBT on addition of NaNbO3 is exhibited in the material as observed from Fourier-transform infrared spectroscopy (FT-IR) spectrum. The optical band gap energy of the sample is determined from the diffused absorbance spectra to be 3.2eV, which may be useful in photo-catalytic application. In the frequency range of 130-900cm(-1), different vibrational modes are observed from Raman spectrum. Field emission scanning electron microscopy (FE-SEM) images reveal a well-defined and homogeneous morphology. Polarization vs. electric field study confirms the ferroelectricity. Dielectric and complex impedance spectroscopic studies are performed over a wide range of frequency (i.e., 10(3)-10(6)Hz) and temperature (30 degrees-500 degrees C) and it is found that Jonscher's power law is well applicable to the alternating current (ac) conductivity spectrum. The direct current (dc) conductivity of the material, which depends upon temperature, exhibits the decrease resistance with increase of temperature similar to that of semiconductors. The dc conductivity confirms that the conduction mechanism is influenced by oxygen vacancies.