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

Composition driven crossover from ferroelectric (FE) to relaxor-ferroelectric (RFE) is systematically investigated in (0.8-x)(Na0.5Bi0.5)TiO3-0.2SrTiO(3)-x(K0.5Na0.5)NbO3 (NBT-ST-xKNN) ceramics in the light of ferroelectric and dielectric (epsilon) 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 maximume similar to 4200 and tan delta < 0.1 at x = 0.02. Broad epsilon(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 epsilon(T) profiles resulting in a temperature-insensitive permittivity variation of +/- 15% (epsilon 125 C,100 kHz-similar to 2007) over a span of-280 C. A remarkably low (TC epsilon)(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.