Role of Sintering Temperature on Structure, Conduction Mechanism, Dielectric and Ferroelectric Properties of Li-Doped Knn Ferroelectric Ceramics with Zno as Sintering Aid

Abstract

Lead-free ferroelectric ceramics with chemical composition K0.47Na0.47Li0.06NbO3 was prepared by high-energy ball milling from the high-purity (99%) analytical reagents. The material was calcined at 850⁰C for 4h and sintered using a two-step sintering technique at three different groups of temperatures T1 for 5min and T2 for 4h viz (T1 = 950°C/ T2 = 850°C), (T1 = 1000°C/ T2 = 900°C) and (T1 = 1050°C / T2 = 950°C). The role of different sintering temperatures on the structural, microstructural and compositional properties of the materials was studied using X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive spectroscopy (EDS). Electrical properties like impedance, dielectric constant, dielectric loss and PE-loops of the sintered samples are explored and presented in the paper. SEM micrograph and EDS spectrum analysis suggest the possibility of the dominance of the surface diffusion over the grain boundary diffusion during the sintering process. The non-Debye type of relaxation mechanism is well-fitted with the experimental observations of electrical properties viz impedance and dielectric constant. The fitting of the observed data of the dielectric constant with the modified Cole-Cole relaxation mechanism indicates the dominancy of the space charge polarisation in the lower frequency region. A significant change in the ferroelectric properties caused by the lattice distortion due to site substitution is observed.

Keywords: Lead-free ceramic, Rietveld refinement, Nyquist plot, Cole-Cole relaxation mechanism, Ferroelectric properties