Structural and electrical characterization of lead-free ferroelectric Na1/2Bi1/2TiO3-BaTiO3 thin films obtained by PLD and RF-PLD

We report structural, dielectric and ferroelectric properties of sodium bismuth titanate-barium titanate, 0.94 Na0.5Bi0.5TiO3-0.06 BaTiO3, thin films grown on Pt(1 1 1)/Si by pulsed laser deposition and radiofrequency beam discharge assisted pulsed laser deposition. Structural investigations show that XRD spectra of the films grown by pulsed laser deposition correspond to single-phase pseudoperovskite and indicate coexistence of rhombohedral and tetragonal phases (morphotropic phase boundary), as for the target. These films are polycrystalline and randomly oriented. The spectra of films grown by radiofrequency beam discharge assisted pulsed laser deposition correspond to (0 0 1)-oriented single-phase pseudoperovskite with rhombohedral distortion, as if the morphotropic phase boundary would be displaced towards a slightly higher barium titanate content. Since the other deposition parameters have been the same, it seems that radiofrequency beam discharge assisted pulsed laser deposition induced a higher stress in the deposited films than the first growth technique and favoured the rhombohedral structure. Dielectric measurements show that the temperatures of the dielectric anomalies corresponding to ferroelectric-antiferroelectric-paraelectric transitions are higher that in target material for both sets of films. The relative dielectric constant was about 850 for PLD-grown films and about 1100 for RF-PLD grown films, while the loss tangent was about 0.05 for both sets of films. Polarization-electric field hysteresis loop shows small values of the remanent polarization (below 1 μC/cm2) and coercive field (5 kV/cm), since achieving of saturation values of remanent polarization was prevented by the low effective breakdown field of both sets of films