The present invention relates, in general terms, to piezoelectric thin films with an empirical formula (K1xNax)yNbO3, wherein 0≤x≤1 and 0.64≤y≤0.95. In particular, the piezoelectric thin film comprises at least two adjacent NbO2 planes in an antiphase boundary, the at least two adjacent NbO2 planes displaced from each other by about half a lattice length in either the (100), (010) or (100) crystallographic plane. The present invention also relates to methods of fabricating the piezoelectric thin films.