Misfit strain relaxation in (Ba0.60Sr0.40)TiO3 epitaxial thin films on orthorhombic NdGaO3 substrates

Strain relaxation in (Ba0.60Sr0.40)TiO3 (BST) thin films on < 110 > orthorhombic NdGaO3 substrates is investigated by x-ray diffractometry. Pole figure analysis indicates a [010](BST)parallel to[(1) over bar 00](NGO) and [001](BST)parallel to[001](NGO) in-plane and [100](BST)parallel to[100](NGO) out-of-plane epitaxial relationship. The residual strains are relaxed at h similar to 200 nm, and for h > 600 nm, films are essentially strain free. Two independent dislocations mechanisms operate to relieve the anisotropic misfit strains along the principal directions. The critical thickness for misfit dislocation formation along [001] and [010] are 11 and 15 nm, respectively. Stress analysis indicates deviation from linear elasticity for h < 200. The films with 10 < h < 25 nm are of monoclinic symmetry due to A finite principal shear stress along [110] of the initial orthorhombic cell. (c) 2006 American Institute of Physics.