CORRECTION FOR THE DYNAMICAL ELECTRON-DIFFRACTION EFFECT IN CRYSTAL-STRUCTURE ANALYSIS

A method is proposed to correct for the dynamical electron diffraction effect in crystal structure analysis. A rough structure model is firs t obtained by conventional structure-analysis methods neglecting the d ynamical diffraction effect. From the rough structure model, multislic e calculations are used to estimate the crystal thickness through the observed dynamical diffraction wave amplitudes. With this estimated th ickness, the observed diffraction wave amplitudes are calibrated to gi ve a set of fictitious observed kinematic structure-factor magnitudes. Based on such a set of magnitudes, a traditional least-squares proced ure is used to refine structural parameters. The reliability of the re sult is checked by the consistency between the observed dynamical diff raction wave amplitudes and those found from the multislice calculatio n. The process can be made iterative. Tests were performed with two kn own structures, Bi-2212 and Pb-doped Bi-2223 high-T(c) superconductors , and satisfactory results were obtained.