Influence of growth oxygen pressure on the electrical properties and phase transformation of the epitaxial (K,Na)NbO_3-based lead-free ferroelectric films

摘要

The influence of the growth oxygen pressure (GP_(O2)) on the performance of the epitaxial 0.95(K_(0.49)Na_(0.49)Li_(0.02))(Ta_(0.2)Nb_(0.8))O_3-0.05CaZrO_3 with 2wt. % MnO_2 addition (KNNLT-CZM) lead-free ferroelectric films grown on the La_(0.07)Ba_(0.93)SnO_3-coated SrTiO_3 (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 (T_(O-T)) of the KNNLT-CZM films grown at 15 Pa is ~180 °C, which is much lower than ~210 °C of those grown at 25/35 Pa. GP_(O2) is proven to be an important factor that regulating the ferroelectricity and T_(O-T) of the epitaxial KNNLT-CZM films.