• journal_title：American Mineralogist
• Contributor：Ferdinando Bosi ; Giovanni B. Andreozzi ; Ulf Hålenius ; Henrik Skogby
• Publisher：Mineralogical Society of America
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2011.3696
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：96
• issue：4
• firstpage：594
• section：Articles

Six synthetic single crystals of spinel phases with different compositions along the ZnAl₂O₄-ZnCr₂O₄ solid solution were structurally and chemically characterized by X-ray diffraction and electron microprobe techniques. As predicted, unit-cell parameters and octahedral bond lengths (M-O) increase with increasing replacement of Al³⁺ by Cr³⁺. Despite the constant occupancy of the T site by Zn, also the tetrahedral bond length ^TZn-O shows significant variations along this binary. These variations are positively correlated with variations in M-O bond lengths.

The present data in conjunction with data from literature provide a basis for quantitative analyses of the variation in ^TZn-O in normal spinel structures. A negative correlation between ^TZn-O and the ionic potential at M (^MIP) suggests that increasing ^MIP is related to a stronger electrostatic cation-cation repulsion across the shared octahedral edge ^M(O-O)_shared of the structure. An observed negative correlation between ^MIP and ^M(O-O)_shared suggests that a decrease of ^M(O-O)_shared provides a more efficient shielding effect to reduce the octahedral cation interactions.

In normal ZnB₂O₄ spinels (where B = Al³⁺, Cr³⁺, Ga³⁺, V³⁺, Fe³⁺, and Mn³⁺) cations with a smaller size provides a higher charge density. Increasing charge density at the M site causes shortening of ^M(O-O)_shared, which in turn results in shorter ^TZn-O bond length. In general, variations in ^TZn-O are required by the structure to better provide an oxygen shielding effect to the octahedral cation-cation repulsion.