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.

The real structures of α-Al₂O_{3 – 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 C_a = 8 × 10¹⁶ cm^–3 for the radiation-sensitive crystal and C_a < 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 (C_a < 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 C_a = 8 × 10¹⁶ cm^–3. [ABSTRACT FROM AUTHOR]