Anisotropic ferroelectric properties of anisotropically strained epitaxial NaNbO3 films

Abstract

Epitaxial c-axis oriented NaNbO3 films are grown on (110) oriented NdGaO3 substrates. Due to the incorporated lattice strain the films show relaxor ferroelectric properties and an in-plane permittivity that is strongly enhanced with respect to unstrained NaNbO3. Moreover, the lattice mismatch between substrate and film leads to an anisotropy in the compressive in-plain strain of −0.67% and −1.33% for the a- and b-direction of the films, respectively. As a consequence, the ferroelectric properties of the film depend strongly on the orientation of the applied electric field. The small anisotropy of the compressive in-plane strain leads to a large anisotropy of the permittivity, a shift of the peak in the temperature dependence of the permittivity, and different freezing temperatures and activation energies Ea of the relaxor ferroelectric film.