STRUCTURE-OPTICAL PROPERTY CORRELATION OF EPITAXIAL POTASSIUM NIOBATE THIN-FILMS DEPOSITED ON MAGNESIUM-OXIDE(100) SUBSTRATES USING A STRONTIUM-TITANATE TRANSITION LAYER

Epitaxial thin films of orthorhombic KNbO3 (100)/(010) were deposited on MgO (100) single-crystal substrates by pulsed laser ablation using an similar to 120 Angstrom SrTiO3 (110) transition layer in between. From X-ray diffraction, the orientation relationships were determined as (010) [100] or (100) [010] KNbO3 parallel to (110) [1 $($) over bar$$ 10] SrTiO3 parallel to (100) [011] MgO and (010) [001] or (100) [001] KNbO3 parallel to (110) [001] SrTiO3 parallel to (100) [011] MgO. The measured film refractive indices at 632.8 nm were 2.213 +/- 0.003, 2.278 +/- 0.003, and 2.285 +/- 0.003, respectively, along MgO [100], [011], and [011] directions, A model was developed to correlate the measured effective refractive indices of the film to area fractions of domain variants in the film. Using the model, the area fraction of domains with their polarization axis normal to the substrate was estimated to be 60.0 +/- 2.7%.