Abstract
Abstract The crystallization of fresnoite (Ba2TiSi2O8) in supercooled melts can be triggered by the reduction of Ti4+ to Ti3+. We address the question of whether Ti3+ is incorporated into the fresnoite crystal structure during such electrochemically induced crystallization. Fresnoite crystals grown from a variety of highly reduced melts were studied by electron energy-loss spectroscopy in order to distinguish between Ti3+ and Ti4+ contents in the corresponding phases. Although the presence of Ti3+ strongly promotes crystallization, Ti3+ is not incorporated into the fresnoite crystal lattice in a significant amount (less than 10at.%) but, at sufficiently high Ti3+ concentrations, forms a previously unreported barium oxotitanate(III) containing trivalent titanium only. Since, in the fresnoite crystal structure, Ti4+ solely adopts an unusual fivefold co-ordination, we also discuss the energy-loss near-edge structure (ELNES) of the Ti L2,3 ionization edge and compare it with the Ti L2,3 ELNES of tetrahedrally and octahedrally coordinated Ti4+.
Published Version
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