We have noticed in α-LiIO3 single crystals the following experimental facts: (1) Using the conoscopic observation method, it was found the contrast of layer imperfections increasing with the strength of a dc field. (2) Changes take place in the x-ray topography under the action of a dc field. (3) The grown-in spatial variation of lattice parameters were found and measured by an x-ray double-crystal spectrometer. Based on these observations, we infer that space charges (carriers, impurity ions and vacancies) are accumulated at the defects of macroscopic scale, which in turn produces a gradient of lattice parameters under the action of a dc field. We calculated the neutron Bragg scattering cross section for a distorted single crystal using the Born approximation and taking into account the extinction at the same time. Therefrom, the enhancement of diffraction in an α-LiIO3 crystal under the action of a dc field were qualitatively interpreted with good agreement.
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