  Solid solutions of SiO2 and B2O3 in Li2O 2SiO2 are synthesized and
characterized for the first time. Their structure and crystallization
mechanisms are investigated employing a combination of simulations at the
density functional theory level and experiments on the crystallization of SiO2
and B2O3 doped lithium disilicate glasses. The remarkable agreement of
calculated and experimentally determined cell parameters reveals the
preferential, kinetically controlled incorporation of [SiO4] and [BO4] at the
Li+ lattice sites of the Li2O 2SiO2 crystal structure. While the addition of
SiO2 increases the glass viscosity resulting in lower crystal growth
velocities, glasses containing B2O3 show a reduction of both viscosities and
crystal growth velocities. These observations could be rationalized by a change
of the chemical composition of the glass matrix surrounding the precipitated
crystal phase during the course of crystallization, which leads to a
deceleration of the attachment of building units required for further crystal
growth at the liquid-crystal interface.
