Sodalite-like layer structures in the series 4CaO*3Al203*3H20 —4CaO~*3Ga_2O_3~*3H2_O,and their three-dimensional sodalite-typedehydration products: The first gallate–sodalite established.

摘要

Aluminate sodalites have been known for quite a long time, and received some attention because oftheir wealth of structural phase transitions and modulated phases. The preparation of gallate sodalitesremained a challenge. We have now succeeded in the preparation, and characterization, of mixedaluminate-gallate and of pure gallate sodalites. In order to do so we had to employ a three-stepprocedure. First, oxide precursors were prepared in the right stoichiometry which were then transformed hydrothermally into members of the solid solution series 4CaO*3Al203*3H20 —4CaO*3Ga203*3H20. Finally, three-dimensional sodalites were obtained by careful dehydration. The intermediate products formed were studied by X-ray powder diffraction, electron microprobe analysisand FTIR spectroscopy, and it was found that they all have structures which can be described asinterrupted sodalite structures, or perhaps more appropriately as layered sodalites. No miscibility-gapswere observed in the series of eleven compounds, and the IR-spectra, lattice parameters and bondlengths in the solid solution series vary smoothly with composition. The volume increase from the Al-to the Ga-endmember is -5.4 %, the average T-0-bond length increases linearly from 1.75(1) A forthe aluminate to 1.84(1) A for the gallate.