Determination of the Mean-Statistical Positions of Atoms in a Corundum Structure from the Data of a Neutron-Diffraction Experiment Performed on Highly Fragmented Crystals of α-Al2O3 – δ

Abstract

The real structures of α-Al2O3 – δ anion-deficient corundum crystals characterized by a nonstoichiometry level of δ ~ 0.001, which are applied in X-ray, gamma and beta dosimetry, are neutronographically investigated for the first time. Neutron-scattering measurements are performed on two crystals sintered by the Stepanov method; the anion-vacancy contents are Ca = 8 × 1016 cm–3 for the radiation-sensitive crystal and Ca < 1014 cm–3 for the crystal taken after annealing in an oxygen atmosphere and not sensitive to radiation. With pronounced indications of significant fragmentedness revealed from attestation of these two crystals, in both cases the corundum structure is recognized, and the lattice parameters and atomic coordinates were found. Three approaches are considered for processing the neutron-scattering data obtained from the crystal with the smallest oxygen deficiency (Ca < 1014 cm–3), with the measured intensities corrected in different ways. The best results, which are numerically identical within the framework of the three considered approaches, are extracted from the “ideal crystal” model. The obtained results are verified for the structure characterized by Ca = 8 × 1016 cm–3.