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

• (K0.5Na0.5)NbO3 and [(K0.5Na0.5)0.985La0.005]NbO3 thin films have been prepared.
• The obtained thin films show an excellent (100) preferred orientation.
• Doping with lanthanum results in a decrease of the leakage current density.
• The dielectric properties are enhanced when doping with lanthanum.

Lead-free (K,Na)NbO3 (KNN) and La doped (K,Na)NbO3 (KNN-La) thin films are grown on SrTiO3 substrates using the chemical solution deposition method. The effect of adding different amounts of Na and K excess (0–20 mol%) is investigated. The results confirm the necessity of adding 20 mol% excess amounts of Na and K precursor solutions in order to avoid the formation of the secondary phase, K4Nb6O17, as 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 of the [100] orientation of the substrate. Doping with lanthanum results in a decrease of the leakage current density at low electric field, and an increase in the dielectric permittivity across the whole temperature range (80–380 K). Although the (100)-oriented KNN and KNN-La films exhibited rounded hysteresis loops, at low temperatures the films show the typical ferroelectric hysteresis loops.