Downward self‐polarization of lead‐free (K0.5Na0.5)(Mn0.005Nb0.995)O3 ferroelectric thin films on Nb:SrTiO3 substrate

Spontaneously appearing macroscopic polarization (self‐polarization) 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)O3 (KNMN) thin film was grown on Nb:SrTiO3 single‐crystal substrate and the resultant self‐polarization behavior due to strain relaxation was investigated. 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. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) Downward self‐polarization was observed and studied in (100) preferred‐oriented (K0.5Na0.5)(Mn0.005Nb0.995)O3 (KNMN) ferroelectric thin film on Nb:SrTiO3 (Nb:STO) substrate. Compressive strain occurred due to lattice mismatching and a difference in thermal expansion coefficients (TEC) between the film and Nb:STO substrate. The compressive strain gradient may be the main reason for the observed downward self‐polarization in the KNMN film on Nb:STO substrate.