THE ROLE OF TI4+ ON THE STRUCTURE AND TRANSFORMATIONS OF GEL-PRODUCED ZN2SIO4

The structure and nonisothermal transformations of gel-produced Zn2SiO4 containing a minor amount (5 mole%) of TiO2 precursor (titanium n-propoxide) were studied. Evidence from infrared and Raman spectroscopy indicated that the dissolved Ti4+ enhanced the formation of silicate clusters. On the other hand, Ti4+ became tetrahedrally coordinated when the gel transformed into the p and subsequently the a phase. The presence of Ti4+ lowered the onset and peak temperatures of the transformation in the differential thermal analysis but increased the apparent activation energy for both the crystallization and the beta --> alpha transformation. Ti4+ also resulted in early site saturation for crystallization and slightly delayed site saturation in the subsequent beta --> alpha transformation. This can be accounted for by the effect of Ti4+ on the number of bulk nucleation sites, viz. SiO4 in the gel and TiO4 or lattice imperfections in the beta phase. (C) 1994 Academic Press, Inc.