Optimizing synthesis of Na2Ti2SiO7 • 2H2O (Na-CST) and ion exchange pathways for Cs0.4H1.6Ti2SiO7 • H2O (Cs-CST) determined from in situ synchrotron X-ray powder diffraction

Observation of wide angle diffraction data collected in situ during synthesis of Na-CST (Na2Ti2O3SiO4 (.) 2H(2)O) showed initial crystallization of a precursor phase (SNT) at 30 degrees C followed by conversion to CST after 1 h at 220 degrees C. In situ studies of Cs+ ion exchange into the H+ form of CST showed a site-by-site ion exchange pathway accompanied by a simultaneous structural transition from P4(2)/mbc (cell parameters a = 11.0690(6) angstrom, c = 11.8842(6) angstrom) to P4(2)/mcm (cell parameters a = 7.847(2) angstrom, c = 11.9100(6) angstrom). After approximately 18% Cs+ exchange into site designated Cs2 in space group P4(2)/mcm, a site designated Cs1 in space group P4(2)/mcm began to fill at the center of the 8MR windows until a maximum of approximately 22% exchange was achieved for Cs1. Bond valence sums of site Cs1 to framework O2- are 1.00 v.u., while bond valence sums of site Cs2 to framework O2- are 0.712 v.u. suggesting Cs1 to have a more stable bonding environment. (c) 2005 Elsevier B.V. All rights reserved.