Structure and crystallization of SiO₂ and B₂O₃ doped lithium disilicate glasses from theory and experiment

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.