Dielectric relaxation and modulus spectroscopy analysis of (Na0:47 K0:47 Li0:06) NbO3 ceramics

Abstract

We have investigated the structure, dielectric and electrical properties of lead-free polycrystalline (Na0:47 K0:47 Li0:06) NbO3 ceramics as a function of temperature and frequency in order to understand the intrinsic contribution of grain/bulk and grain boundary effects toward the dielectric response as well as the electrical conduction mechanism in the samples fabricated by microwave sintering method. X-ray diffraction analysis exhibits perovskite structure with orthorhombic symmetry, which is well supported by the Raman spectroscopic analysis. A minor secondary impurity phase of tungsten bronze structure was observed for samples sintered at 1050°C, which gets weaker for samples sintered at 1150°C. Dielectric permittivity was enhanced by 50%, although there was a reduction in the dielectric loss by about 50% at Curie temperature (450°C) for samples sintered at 1150°C. Complex impedance spectroscopic analysis indicated non-Debye-type dielectric relaxation present in the samples, and this phenomenon followed thermally activated process related to hopping mechanism. Nyquist plot showed the negative temperature coefficient of resistance, characteristic of the samples.