Influence of growth oxygen pressure on the electrical properties and phase transformation of the epitaxial (K,Na)NbO3-based lead-free ferroelectric films

The influence of the growth oxygen pressure (GPO(2)) on the performance of the epitaxial 0.95(K0.49Na0.49Li0.02)(Ta0.2Nb0.8)O-3-0.05CaZrO(3) with 2 wt. % MnO2 addition (KNNLT-CZM) lead-free ferroelectric films grown on the La0.07Ba0.93SnO3-coated SrTiO3 (001) substrates is investigated. The x-ray diffraction results show that the tetragonality of the KNNLT-CZM films is dependent on GP(O2), which varies from 0.999 at 15 Pa to 1.006 at 35 Pa. Since the polarization direction with applied electrical field of the (010)-oriented KNN-based film is along [110]/[011], the relationship between the ferroelectricity and GP(O2) is well explained from the perspective of the tetragonality change. The leakage current density of the KNNLT-CZM films is suppressed and the dielectric constant is enhanced from 427 to 1538 at 1 kHz with increasing the GP(O2). Moreover, the orthorhombic to tetragonal phase transition temperature (TO-T) of the KNNLT-CZM films grown at 15 Pa is similar to 180 degrees C, which is much lower than similar to 210 degrees C of those grown at 25/35 Pa. GP(O2) is proven to be an important factor that regulating the ferroelectricity and TO-T of the epitaxial KNNLT-CZM films.