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We report the observation of a strong second-order nonlinear optical response from epitaxial Ba[sub 0.48]Sr[sub 0.52]TiO[sub 3] thin films grown on MgO(001) by magnetron sputtering. The result is unexpected since the crystal structure of Ba[sub 0.48]Sr[sub 0.52]TiO[sub 3] is centrosymmetric under ambient conditions. A second-order nonlinear susceptibility d[sub 33] as large as 11 pm/V at a fundamental wavelength of 1.064 μm is observed in a 300 Å thick film. By studying a series of films with different strains, induced by a film-substrate lattice mismatch, we conclude that the resulting tetragonal distortion, presumably accompanied by a loss of inversion symmetry, is responsible for the second-harmonic generation. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The formation of crystalline Ba-ferrite/sapphire(001) films in an amorphous precursor during annealing was studied in a real-time synchrotron x-ray scattering experiment. From the x-ray integrated intensity and the surface morphology, we found that the crystalline Ba-ferrite phase was formed by solid phase transformation of the intermediate crystalline α-Fe[sub 2]O[sub 3] phase, not by direct crystallization of the amorphous precursor. The solid phase transformation occurred at temperature above 500 °C. The high crystallization temperature of the Ba-ferrite phase was attributed to the activation barrier for the diffusion of Ba ions into the α-Fe[sub 2]O[sub 3] phase. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]