• journal_title：American Mineralogist
• Contributor：Ulf Hålenius ; Ferdinando Bosi ; Henrik Skogby
• Publisher：Mineralogical Society of America
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2011.3700
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：96
• issue：4
• firstpage：617
• section：Articles

Optical absorption spectroscopy and X-ray structural refinements of seven different spinel single crystals on the (Mg_1−xMn_x)Al₂O₄ solid solution (x = 0.02–1.00) evidences exceptionally strong relaxation (ε = 0.83) of ^IVMn²⁺-O bonds. Our single-crystal structure refinements demonstrate that the ideal ^IVMn²⁺-O bond distance in fully ordered galaxite (MnAl₂O₄) should be 2.050 Å, which is 0.014 Å longer than previously suggested, and that structural parameters are mainly affected by the variations occurring at the TO₄ tetrahedron. The very strong structural relaxation observed around the T site may be explained by the fact that the TO₄ polyhedra of the spinel structure share only corners with neighboring MO₆ octahedra and are fully isolated from neighboring TO₄ tetrahedra. This provides structural flexibility around the T site and allows for considerable local T-O bond distance variations.