Study epitaxially strained KNbO3/NaNbO3 superlattice using first-principle's calculations

The changes of crystal structure, zone-center phonon, polarization and dielectric constant with epitaxial strain in KNbO3/NaNbO3 (KNO/NNO) superlattice have been studied using density functional theory (DFT) within the local-density approximation (LDA). Strain induced structural phase transitions have been identified from tetragonal to monoclinic then to orthorhombic when the in plane misfit strain changes from -1.25% to -0.1%. The polarization amplitude is the highest in the orthorhombic phase, reaching more than 70 mu C/cm(2), and the dielectric constant peaks at the phase boundaries.