Anisotropic strain relaxation in (Ba0.6Sr0.4)Tio3 epitaxial thin films -: art. no. 103530

We have studied the evolution of anisotropic epitaxial strains in < 110 >-oriented (Ba0.60Sr0.40)TiO3 paraelectric (m3m) thin films grown on orthorhombic (mm2) < 100 >-oriented NdGaO3 by high-resolution x-ray diffractometry. All the six independent components of the three-dimensional strain tensor were measured in films with 25-1200-nm thickness, from which the principal stresses and strains were obtained. Pole figure analysis indicated that the epitaxial relations are [001](m3m)parallel to[001](mm2) and [110](m3m)parallel to[010](mm2) in the plane of the film, and [110](m3m)parallel to[100](mm2) along the growth direction. The dislocation system responsible for strain relief along [001] has been determined to be vertical bar b vertical bar((001))= 3/4 vertical bar b vertical bar. Strain relief along the [110] direction, on the other hand, has been determined to be due to a coupled mechanism given by vertical bar b vertical bar((1) over bar 10))=vertical bar b vertical bar and vertical bar b vertical bar (((1) over bar 00)) = root 3/4 vertical bar b vertical bar. Critical thicknesses, as determined from nonlinear regression using the Matthews-Blakeslee equation, for misfit dislocation formation along [001] and [(1) over bar 00] direction were found to be 5 and 7 nm, respectively. The residual strain energy density was calculated as similar to 2.9 x 10(6) J/m(3) at 25 nm, which was found to relax an order of magnitude by 200 nm. At 200 nm, the linear dislocation density along [001] and [(1) over bar 10] are similar to 6.5 x 10(5) and similar to 6 x 10(5) cm(-1), respectively. For films thicker than 600 nm, additional strain relief occurred through surface undulations, indicating that this secondary strain-relief mechanism is a volume effect that sets in upon cooling from the growth temperature. (c) 2005 American Institute of Physics.