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

Abstract

We report the growth of single-phase (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films on SrRuO3 coated ⟨001⟩ oriented SrTiO3 substrates by using pulsed laser deposition. Films grown at 600°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°C. However, films deposited at lower temperatures exhibit compositional fluctuations as verified by Rutherford backscattering spectroscopy. The epitaxial films of 400–600nm thickness have a room temperature relative permittivity of ∼750 and a loss tangent of ∼6% at 1kHz. The room temperature remnant polarization of the films is 4μC∕cm2, while the saturation polarization is 7.1μC∕cm2 at 24kV∕cm and the coercive field is ∼7.3kV∕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.