Structural features and isomorphous substitutions in chromium- and magnesium-containing beryls and chromium-containing beryllian indialite grown by the flux method

• Published in: Crystallography reports 2009-03, Vol.54 (2), p.203-210
• Main Authors: Mikhaĭlov, M. A., Rozhdestvenskaya, I. V., Bannova, I. I., Matveeva, L. N., Demina, T. V.
• Format: Article
• Language: English
• Subjects: BERYL; BOND LENGTHS; CHROMIUM; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CRYSTAL GROWTH; Crystallography and Scattering Methods; MAGNESIUM; Physics; Physics and Astronomy; Structure of Inorganic Compounds; X-RAY DIFFRACTION
• ISSN: 1063-7745; 1562-689X
• DOI: 10.1134/S1063774509020072

Beryls and beryllian indialite {the general formula M VI 2 T (2) IV 3 T (1) IV 6 O 18 } synthesized in magnesium-containing flux systems saturated with chromium are investigated using X-ray diffraction. The isovalent schemes of the isomorphous incorporation of chromium into M octahedra of these compounds and the simultaneously realized heterovalent schemes with the participation of other components are revealed from the occupancies of the positions. It is demonstrated that an increase in the average bond lengths in the M positions leads predominantly to an increase in the parameter α . In the beryllian indialites, the T (1) tetrahedra are substantially closer to perfect tetrahedra, the T (2) tetrahedra are distorted to a lesser extent, and the M octahedra are distorted to a greater extent than those in beryls. The structural indications of the ability of compounds with a beryl structure to congruently melt are distinguished.