Cation ordering over short-range and long-range scales in the MgAl2O4-CuAl2O4 series
-
Rosa Anna Fregola
,
Ferdinando Bosi
Abstract
A multi-analytical approach using electron microprobe analysis, X-ray structural refinement, and optical absorption spectroscopy was applied to characterize short-range and long-range structures of synthetic spinel single crystals along the MgAl2O4-CuAl2O4 solid-solution series. Site populations, derived from the results of site-scattering refinement and stereochemical analysis, show that the tetrahedrally coordinated site (T) is mainly populated by Mg and Cu2+, while the octahedrally coordinated site (M) is dominated by Al. Crystals also show a significant degree of inversion, i.e., occurrence of Al at T counterbalanced by occurrence of divalent cations at M, which increases slightly from 0.24 to 0.29 for the highest Cu2+ contents. Short-range information derived from optical spectra suggests that the local TCu2+-O distances remain constant at increasing Cu2+ content, whereas local MCu2+-O distances are ca. 0.02 Å shorter in Cu-poor MgAl2O4 spinels as compared to MCu2+-O distances in end-member CuAl2O4. The observed splitting of an absorption band, at ca. 7000 cm-1 , caused by electron transitions in TCu2+ as well as the anomalous broadness of an absorption band, at ca. 13 500 cm-1, caused by electron transitions in MCu2+ indicates the occurrence of local Jahn-Teller distortions at T and M. Long-range information, however, shows no violation of Fd3m symmetry. From refinements of our single-crystal XRD data we could for the first time derive for a cubic spinel phase a MCu2+-O distance of 2.080 Å and a TCu2+-O of 1.960 Å. The very limited variations in the unit-cell parameter a from 8.079 to 8.087 Å are mainly related to the disordering of Al. Because of the very similar size of Cu2+ and Mg at the T and M sites, the spinel structure responds to the Cu2+ → Mg substitution by increasing cation disordering in such a manner that mean M-O distances remain constant and the mean T-O distances decrease slightly. This results in increasing length of shared octahedral edges and thereby increase of the octahedral cation-cation repulsion. In line with other studies, the importance of steric factors for controlling the cation distributions in the spinel structure is demonstrated to be valid also in the MgAl2O4-CuAl2O4 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
