Preparation and characterization of sol–gel derived sodium–potassium bismuth titanate powders and thick films deposited by screen printing

Bi0.5(Na0.82K0.18)0.5TiO3 (NKBT) lead-free thick films have been successfully deposited on Pt electroded alumina substrates using screen printing from the sol–gel derived powders. Fourier transform infrared (FT-IR) spectroscopy, differential thermal analysis (DTA), thermogravimetric analysis (TG) and X-ray diffraction (XRD) were used to characterize the process of crystallization. The cubic shape particulates of the order of 140–260 nm in size can be obtained by calcining the xerogel at 650 °C, and there is no obvious agglomeration of the NKBT powders. The resulting typical 90 μm thick NKBT films sintered at 1140 °C exhibit relative dielectric constant of 836 (at 10 kHz), dielectric constant of 2.9%, remanent polarization of 25.6 μC/cm2, coercive field of 69.3 kV/cm, and longitudinal effective piezoelectric coefficient, d33eff of 95 pm/V. The improvement of the electric properties can be attributed to the larger domain wall density and less domain wall pinning resulting from the increased film thickness of NKBT thick films.