Blue spinel crystals in the MgAl2O4-CoAl2O4 series: Part II. Cation ordering over short-range and long-range scales
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Abstract
Optical absorption spectroscopy and X-ray structural refinements were used to characterize short-range and long-range structures of 10 gem-quality, blue spinel single crystals synthesized on the (Mg1-xCox) Al2O4 solid solution (x = 0.07-1.00). The site distributions of Mg, Co2+, and Al show that the tetrahedrally coordinated site (T) is mainly populated by Mg and Co2+, with a marked preference of Co2+ for tetrahedral coordination with respect to Mg, while the octahedrally coordinated site (M) is dominated by Al. Crystals also show a certain degree of inversion, i.e., occurrence of Al at T counterbalanced by the occurrence of divalent cations at M, which decreases from 0.24 to 0.13 with increasing Co2+ content.
Short-range information based on the crystal field splitting parameter Dq derived from single-crystal optical spectra suggests that the local Co2+-O bond length at the T-site may increase marginally at increasing Co2+ content. An almost constant value for the Racah B-parameter, also derived from optical spectra, for tetrahedrally coordinated Co2+ suggests that any influence of substitutional second nearest neighbor cations on the ionicity of Co2+-O bonds at the T-site is very small. Long-range information shows that variations in the unit-cell parameter from 8.084 to 8.105 Å along the solid-solution series are mainly related to the ordering of Al at the M site as a result of the replacement of Mg by Co2+. Therefore, the spinel structure responds to the chemical variation by ordering of Al in such a manner that M-O remains almost constant and T-O increases. In this way, the lengths of shared octahedral edges are reduced and the destabilization effect due to the increased octahedral cation-cation repulsion is minimized. In line with other studies, the importance of steric factors for controlling the cation distributions in the spinel structure has also been shown to be valid in the MgAl2O4-CoAl2O4 solid-solution series.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- Cation ordering over short-range and long-range scales in the MgAl2O4-CuAl2O4 series
- Blue spinel crystals in the MgAl2O4-CoAl2O4 series: Part I. Flux growth and chemical characterization
- Blue spinel crystals in the MgAl2O4-CoAl2O4 series: Part II. Cation ordering over short-range and long-range scales
- CO2 solubility in primitive martian basalts similar to Yamato 980459, the effect of composition on CO2 solubility of basalts, and the evolution of the martian atmosphere
- New structural features of the high-pressure synthetic sheet-disilicate Phase-X, K(2–x)Mg2Si2O7Hx
- Crystal structure refinements of borate dimorphs inderite and kurnakovite using 11B and 25Mg nuclear magnetic resonance and DFT calculations
- Hydrogen-bond system and dehydration behavior of the natural zeolite parthéite
- In situ dehydration behavior of zeolite-like cavansite: A single-crystal X-ray study
- LREE-redistribution among fluorapatite, monazite, and allanite at high pressures and temperatures
- A single-crystal neutron diffraction study of hambergite, Be2BO3(OH,F)
- Analyzing water contents in unexposed glass inclusions in quartz crystals
- The atomic structure of deuterated boyleite ZnSO4·4D2O, ilesite MnSO4·4D2O, and bianchite ZnSO4·6D2O
- Synthesis and crystal chemistry of Fe3+-bearing (Mg,Fe3+)(Si,Fe3+)O3 perovskite
- Mixed-layered structure formation during trans-vacant Al-rich illite partial dehydroxylation
- Structural regularities in 2M1 dioctahedral micas: The structure modeling approach
- Incorporation of Fe and Al in MgSiO3 perovskite: An investigation by 27Al and 29Si NMR spectroscopy
- In situ high-temperature Raman and FTIR spectroscopy of the phase transformation of lizardite
- Packing systematics and structural relationships of the new copper molybdate markascherite and related minerals
- On the origin of sellaite (MgF2)-rich deposits in Mg-poor environments
- Edgrewite Ca9(SiO4)4F2-hydroxyledgrewite Ca9(SiO4)4(OH)2, a new series of calcium humite-group minerals from altered xenoliths in the ignimbrite of Upper Chegem caldera, Northern Caucasus, Kabardino-Balkaria, Russia
- Whelanite, Cu2Ca6[Si6O17(OH)](CO3)(OH)3(H2O)2, an (old) new mineral from the Bawana mine, Milford, Utah
- 2M1-phlogopite from Black Hills (South Australia): The first case of configurational polytype in micas
- Oxy-chromium-dravite, NaCr3(Cr4Mg2)(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup
- First-principles study of self-diffusion and viscous flow in diopside (CaMgSi2O6) liquid
- Browneite, MnS, a new sphalerite-group mineral from the Zakłodzie meteorite
- Mineralogical variation of silica induced by Al and Na in hydrothermal solutions
Articles in the same Issue
- Cation ordering over short-range and long-range scales in the MgAl2O4-CuAl2O4 series
- Blue spinel crystals in the MgAl2O4-CoAl2O4 series: Part I. Flux growth and chemical characterization
- Blue spinel crystals in the MgAl2O4-CoAl2O4 series: Part II. Cation ordering over short-range and long-range scales
- CO2 solubility in primitive martian basalts similar to Yamato 980459, the effect of composition on CO2 solubility of basalts, and the evolution of the martian atmosphere
- New structural features of the high-pressure synthetic sheet-disilicate Phase-X, K(2–x)Mg2Si2O7Hx
- Crystal structure refinements of borate dimorphs inderite and kurnakovite using 11B and 25Mg nuclear magnetic resonance and DFT calculations
- Hydrogen-bond system and dehydration behavior of the natural zeolite parthéite
- In situ dehydration behavior of zeolite-like cavansite: A single-crystal X-ray study
- LREE-redistribution among fluorapatite, monazite, and allanite at high pressures and temperatures
- A single-crystal neutron diffraction study of hambergite, Be2BO3(OH,F)
- Analyzing water contents in unexposed glass inclusions in quartz crystals
- The atomic structure of deuterated boyleite ZnSO4·4D2O, ilesite MnSO4·4D2O, and bianchite ZnSO4·6D2O
- Synthesis and crystal chemistry of Fe3+-bearing (Mg,Fe3+)(Si,Fe3+)O3 perovskite
- Mixed-layered structure formation during trans-vacant Al-rich illite partial dehydroxylation
- Structural regularities in 2M1 dioctahedral micas: The structure modeling approach
- Incorporation of Fe and Al in MgSiO3 perovskite: An investigation by 27Al and 29Si NMR spectroscopy
- In situ high-temperature Raman and FTIR spectroscopy of the phase transformation of lizardite
- Packing systematics and structural relationships of the new copper molybdate markascherite and related minerals
- On the origin of sellaite (MgF2)-rich deposits in Mg-poor environments
- Edgrewite Ca9(SiO4)4F2-hydroxyledgrewite Ca9(SiO4)4(OH)2, a new series of calcium humite-group minerals from altered xenoliths in the ignimbrite of Upper Chegem caldera, Northern Caucasus, Kabardino-Balkaria, Russia
- Whelanite, Cu2Ca6[Si6O17(OH)](CO3)(OH)3(H2O)2, an (old) new mineral from the Bawana mine, Milford, Utah
- 2M1-phlogopite from Black Hills (South Australia): The first case of configurational polytype in micas
- Oxy-chromium-dravite, NaCr3(Cr4Mg2)(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup
- First-principles study of self-diffusion and viscous flow in diopside (CaMgSi2O6) liquid
- Browneite, MnS, a new sphalerite-group mineral from the Zakłodzie meteorite
- Mineralogical variation of silica induced by Al and Na in hydrothermal solutions
