| Abstract
| - Alkali silicotitanate ternary phases have been studied for a wide variety of applicationsincluding catalysis, selective ion exchange, and ceramic nuclear waste form materials. Wereport here the synthesis and structural characterization of Rb2TiSi6O15 and K2TiSi6O15,structural analogues to SNL-A (Cc-Cs2TiSi6O15). The Rb analogue is the first reported ternaryoxide, the rubidium silicotitanate phase. Both the Rb and the K analogues were synthesizednearly pure by hydrothermal treatment of oxide precursor mixtures seeded with SNL-A andcould not be synthesized without the addition of the seed. Rietveld refinement gave goodstructural models in the Cc space group with unit cell parameters: Rb2TiSi6O15, V = 1357.9Å3, a = 12.736(2) Å, b = 7.3392(3) Å, c = 15.061(3) Å, β = 105.29(2)° and K2TiSi6O15, V =1318.5 Å3, a = 12.570(2) Å, b = 7.2534(3) Å, c = 15.082(3) Å, β = 106.49(3)°. The twoisostructural phases were also characterized by thermogravimetry and 29Si NMR. Unit cellparameters, melting temperatures, and 29Si chemical shifts were compared to those of theCs analogue and related to variation in alkali radius (Cs > Rb > K). The volume, the a-axis,and the b-axis increase linearly with alkali radius, which is directly related to a “relaxation”of the folds of the corrugated silicate layers that lie in the xy plane.
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