Ferroelectric, dielectric and leakage current properties of epitaxial (K,Na)NbO3-LiTaO3-CaZrO3 thin films

Epitaxial 0.95(Na-0.49 K0.49Li0.02) (Nb0.8Ta0.2)-0.05CaZrO(3) thin films were deposited under various oxygen pressures (15-45 Pa) and substrate temperatures (600-720 A degrees C) on SrTiO3 (001) substrates using La0.7Sr0.3MnO3 as bottom electrodes. Their microstructures, ferroelectric and dielectric properties were intensively investigated with high-resolution X-ray diffraction (XRD), polarization- electric field hysteresis (P-E) measurements and leakage currents (I-V) characterizations. It is found that the lattice constant of the films increases with increasing deposition temperature, while it nearly keeps a constant even when the oxygen pressures are changed. The crystallinity of the films shows an increment with increasing oxygen partial pressure. Saturated P-E loops are obtained for all the films. The film fabricated with optimized parameters at 680 A degrees C and 35 Pa displays a dielectric constant of 1185 at 1 kHz, a remnant polarization (2P (r)) of 28.0 mu C/cm(2) and a coercive field (2E (c)) of 165.4 kV/cm. I-V results revealed that the ohmic conduction, space charge limited current and Pool-Frenkel model came up as predominant transport mechanism in the films in turn with the increment of applied electric field.