Growth and physical properties of highly oriented La-doped (K,Na)NbO3 ferroelectric thin films

Lead-free (K,Na)NbO3 (KNN) and La doped (K,Na)NbO3 (KNN-La) thin films were grown on SrTiO3 substrates by chemical solution deposition method. The effect of adding different amounts of Na and K excess (0-20 mol%) has been investigated. The results confirm the necessity to add 20 mol% excess amounts of Na and K precursor solutions in order to avoid the formation of the secondary phase, K4Nb6O17, as is confirmed by X-ray diffraction and Raman spectroscopy. Moreover, when adding a 20 mol% of alkaline metal excess the thin films are highly textured with out-of-plane preferential orientation in the [100] direction following the [100] orientation of the substrate. Doping with lanthanum resulted in the decrease in the leakage current density at low electric field, and an increase in the dielectric permittivity across all the temperatures range (80-380 K). Although the (100)-oriented KNN and KNN-La films exhibited rounded hysteresis loops, at low temperature the films showed the typical ferroelectric hysteresis loops.