Pulsed laser deposition of single-phase lead-free NKLNST thin films with K- and Na-excess targets

• PLD growth of NKLNST films was first attempted using targets incorporating excess K and Na.
• Effects of O2 pressure during the PLD process on the films properties were systematically studied.
• Proper amount of excess K (Na) and O2 pressure are key leading to high-quality single-phase films.
• Best-quality film was deposited with the target incorporating 20 mol% excess K and Na at 1 Pa of O2.
• Ohmic conduction and SCLC dominate the transport in the film at low and high fields, respectively.

Lead-free [(Na0.57K0.43)0.94Li0.06][(Nb0.94Sb0.06)0.95Ta0.05]O3 (NKLNST) thin films were prepared on Pt (1 1 1)/Ti/SiO2/Si (0 0 1) substrates by pulsed laser deposition. NKLNST ceramic targets incorporating different amounts of excess K and Na were utilized in order to compensate the K and Na evaporation loss during the films deposition process, and the target containing 20 mol% excess K and Na was found optimal based on the stoichiometry and crystallinity of the resulting films. With such a target and 1 Pa of O2, high-quality NKLNST thin films were deposited, which exhibit a well-crystallized perovskite phase, the densest and smoothest surface and optimum structural and electrical properties, with a remnant polarization Pr of 7.18 μC/cm2. Ohmic conduction dominates the transport at low electric fields (<10 kV/cm) for the film grown at 1 Pa of O2, while space charge-limited current was found to be the governing leakage mechanism at high electric fields. The work unraveled the roles of excess K and Na incorporation in the target and O2 pressure during the PLD process in preserving the volatile K and Na contents and leading eventually to formation of single-phase high-quality KNN-based thin films by pulsed laser deposition.