Effect of Ca on structural and ferroelectric properties of SrBi2Ta2O9 and SrBi2Nb2O9 thin films

In this study, we have improved the remanent polarization of SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN) thin films using Ca substitution at Sr-site. SBT and SBN thin films with different concentrations of Ca were deposited on Pt/TiO2/SiO2/Si substrates using pulsed-laser-deposition technique. The lattice parameters was found to be decreased with Ca incorporation and was attributed to the smaller ionic radii of Ca than for Sr. The modification in lattice vibrational frequencies with the incorporation of Ca in SBT and SBN films was investigated using micro-Raman spectroscopy. The grain size was increased with the increase in the Ca concentrations in SBT and SBN thin films. The SBT thin films with 20% Ca contents exhibited remnant polarization of ∼23.8 μC/cm2 with a coercive field of ∼175 kV/cm. The remanent polarization was found to be ∼35.5 μC/cm2 for SBN thin films with 10% Ca incorporation. The dielectric constant of SBT and SBN films was found to be decrease with Ca concentrations and observed to be independent of grain size.