Composition dependent crossover from ferroelectric to relaxor-ferroelectric in NBT-ST-KNN ceramics

Abstract

Composition driven crossover from ferroelectric (FE) to relaxor-ferroelectric (RFE) is systematically investigated in (0.8-x)(Na0.5Bi0.5)TiO3-0.2SrTiO3-x(K0.5Na0.5)NbO3 (NBT-ST-xKNN) ceramics in the light of ferroelectric and dielectric (ε) response. The appearance of constricted polarization-electric field loop and double current density-electric field peaks in the proximity of x = 0.02 suggests a co-existence of FE and RFE phases. The system attains a maximumε ∼4200 and tan δ < 0.1 at x = 0.02. Broad ε(T) peaks reveal a greater degree of disorder due to KNN substitution and their deconvolution demonstrates three different relaxation/polarization processes related to low and high-temperature nanodomains. The composition with x = 0.1 exhibits maximum broadness in ε(T) profiles resulting in a temperature-insensitive permittivity variation of ±15% (ε125 °C,100kHz∼2007) over a span of ∼280 °C. A remarkably low (TCε)100kHz of −75 ppm/°C is also achieved for x = 0.1 from 100 to 300 °C proposing it to be a potential capacitor material.