Dielectric and ferroelectric properties of strain-relieved epitaxial lead-free KNN-LT-LS ferroelectric thin films on SrTiO3 substrates

We report the growth of single-phase (K-0.44,Na-0.52,Li-0.04)(Nb-0.84,Ta-0.10,Sb-0.06)O-3 thin films on SrRuO3 coated < 001 > oriented SrTiO3 substrates by using pulsed laser deposition. Films grown at 600 degrees C under low laser fluence exhibit a < 001 > textured columnar grained nanostructure, which coalesce with increasing deposition temperature, leading to a uniform fully epitaxial highly stoichiometric film at 750 degrees C. However, films deposited at lower temperatures exhibit compositional fluctuations as verified by Rutherford backscattering spectroscopy. The epitaxial films of 400-600 nm thickness have a room temperature relative permittivity of similar to 750 and a loss tangent of similar to 6% at 1 kHz. The room temperature remnant polarization of the films is 4 mu C/cm(2), while the saturation polarization is 7.1 mu C/cm(2) at 24 kV/cm and the coercive field is similar to 7.3 kV/cm. The results indicate that approximately 50% of the bulk permittivity and 20% of bulk spontaneous polarization can be retained in submicron epitaxial KNN-LT-LS thin film, respectively. The conductivity of the films remains to be a challenge as evidenced by the high loss tangent, leakage currents, and broad hysteresis loops. (c) 2008 American Institute of Physics.