SELECTIVE T-SITE SUBSTITUTION AS A CAUSE OF THE ANISOTROPY OF LATTICEEXPANSION IN TITANOSILICATE-1 INVESTIGATED BY MOLECULAR-DYNAMICS AND COMPUTER-GRAPHICS

The selective substitution of a silicon by titanium in MFI lattice was investigated by molecular dynamics (MD) and computer graphics (CG). I t was demonstrated that the MD method, using a simple two-body interat omic potential, is effective to reproduce the framework structure. The lattice expansion as a function of the location and concentration of Ti in the titanosilicate with the MFI structure (titanosilicate-1, TS- ) was calculated, and the results were consistent with experimental da ta. The anisotropic lattice expansion due to Ti substitution in variou s crystallographic sites of MFI lattice was studied. The favorable sit e for Ti substitution was discussed by comparing the expansions of lat tice parameters reported by X-ray diffraction(XRD) studies. MD and CG are effective methods for explaining the anisotropic lattice expansion and for determining the substituted sites of isomorphous substitution in TS-1.