Methodological features of determining the composition of α-NiSO₄·6H₂O single crystals activated by low concentration Co²⁺ ions: laboratory diffractometer and synchrotron

Crystal activation is one of the effective methods that allows influencing functional properties by the nature of dopant ions and their concentration. The region of low dopant concentrations, which is not well represented in the literature, is of particular methodological, scientific, and applied interest.

This work aims to establish the distribution of Со²⁺ ions in the growth sectors of large-sized (~80×80×50 mm) α-Ni²⁺SO₄·6H₂O crystals, used as solar-blind UV filters, grown from an aqueous solution with 0.36 (α-NSH:0.36Co), 0.68 (α-NSH:0.68Co), and 1.0 wt. % Со (α-NSH:1.0Co).

The unit cell volume (V, ų) of macroparts (~0.25×0.25×0.20 mm; Bruker D8 QUEST PHOTON-III) of α-NSH:Со (sp. gr. P4₁2₁2, Z = 4) decreases in the series V₍₁₀₂₎>V₍₀₀₁₎>V₍₁₀₁₎ (a-NSH:0.36Со), V₍₁₀₂₎>V₍₁₀₁₎>V₍₀₀₁₎ (a-NSH:0.68Со), V₍₁₀₁₎>V₍₁₀₂₎>V₍₀₀₁₎ (a-NSH:1.0Со), as well as V₍₀₀₁₎>V₍₁₀₂₎≈V₍₁₀₁₎ (a-NSH:1.0Со) for microparts (~0.02×0.02×0.02 mm; “Belok/XSA” beamline, Kurchatov Synchrotron Radiation Source). This change in V, ų is caused by a different distribution of Co²⁺ across growth sectors, and for a-NSH:1.0Co, also by different conditions of X-ray experiments. The Co²⁺ content decreases in the series р₍₀₀₁₎>р₍₁₀₁₎>р₍₁₀₂₎ (a-NSH:0.36Со; a-NSH:0.68Со), р₍₁₀₁₎>р₍₁₀₂₎>р₍₀₀₁₎ (a-NSH:1.0Со) (р, site occupancy). Comparison of these series shows the substitution of Co²⁺ for Ni²⁺ ions, a symbate correlation between V, ų and p, p and the D–H and D···A distances, but an antibate correlation between p and the H···A distance for a-NSH:1.0Co.

Funding: Ministry of Science and Higher Education of the Russian Federation, grant № FSFZ-2024-0003.