  Ordering of disordered materials occurs during the activated process of
nucleation that requires the formation of critical clusters that have to
surmount a thermodynamic barrier. The characterization of these clusters is
experimentally challenging but mandatory to improve nucleation theory. In this
paper, the nucleation of a magnesium aluminosilicate glass containing the
nucleating oxide TiO2 is investigated using neutron scattering with Ti isotopic
substitution and 27Al NMR. We identified the structural changes induced by the
formation of crystals around Ti atoms and evidenced important structural
reorganization of the glassy matrix.
