ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
The topotaxy of the reaction of single crystals of periclase, MgO, and β-Ga2O3 to form the spinel MgGa2O4 was investigated by optical and X-ray diffraction techniques after reaction at 1600°C. Three different reaction couples were studied, namely the (001) face of β-Ga2O3 contacting the (001), (110) and (111) surfaces of MgO. The three-dimensional coherency of the oxygen arrangement and packing between each constituent oxide and the spinel reaction product was demonstrated. In both cases the close-packed oxygen planes in the spinel product were aligned parallel to the close-packed oxygen planes in the respective reactant. The topotaxies between the spinel product and the parent crystals were: (a) (111)sp||(013)ga1, [1{\bar 1}0]sp||[100]gai; (b) (111)sp||(111)p, [1{\bar 1}0]sp||[1{\bar 1}0]p. The data for the topotaxy of the spinel reaction product with respect to β-Ga2O3 is fully consistent with an earlier study of the precipitation of β-Ga2O3 from a spinel crystalline solution. This study verified a Wagner-type reaction mechanism where the close-packed oxygen anion structure remains essentially unchanged while the reaction proceeds by a counter diffusion of Mg2+ and Ga3+ ions through the spinel layer formed at the interface. This method of solid-state crystal growth for binary oxide systems at a temperature far below the solidus temperature (∼ 2000°C) can find application in the growth of crystals that decompose or melt ineongruently or that have an undesirable polymorph when solidified directly from the melt.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0567739475001386
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