Downward self-polarization of lead-free (K (0.5) Na (0.5))(Mn (0.005) Nb (0.995)) O-3 ferroelectric thin films on Nb: SrTiO3 substrate

Abstract

Spontaneously appearing macroscopic polarization (selfpolarization) in ferroelectrics without an electrode or an external electric field would enable the freedom to design many ferroelectric heterostructures and devices. The (K0.5Na0.5)(Mn0.005Nb0.995) O-3 (KNMN) thin film was grown on Nb: SrTiO3 single-crystal substrate and the resultant selfpolarization behavior due to strain relaxation was investi-gated. The lattice mismatch and difference in TEC between the KNMN thin film and the Nb: SrTiO3 substrate creates a compressive strain. The compressive strain gradient may be the main cause for the observed downward self-polarization. The downward self-polarization of the KNMN thin film can be explained by the strong inhomogeneous compressive strain caused by strain relaxation.