Structural Refinement of X-Ray Diffraction Profile for Artificial Superlattices

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Abstract
A new structural refinement process for BaTiO3/SrTiO3 (BTO/STO) artificial superlattices was proposed, taking into account the effect of interdiffusion between BTO and STO. The samples were prepared using the molecular beam epitaxy (MBE) method on SrTiO3(001) substrates at 600°C. The step model, the phonon model and the supercell model were employed for simulation of the X-ray diffraction (XRD) profiles of the superlattices. The supercell model can deal with arbitrary variations of chemical composition and lattice spacing. A discrepancy in the intensity of satellite peaks was observed when the interdiffusion between BTO and STO was not incorporated in the simulation. In the phonon model, the concentration profile due to interdiffusion was first calculated using Fick's second law, and the coefficient of Fourier series describing the lattice distortion and modulation of the structure factor was determined. The XRD profiles thus simulated almost agreed with the observed ones, but the intensity of Laue peaks was not consistent with the observation. The degree of interdiffusion at each interface was then changed throughout the superstructures using the supercell model, and it was shown that the accuracy of simulation improved markedly.