The mechanism of deceleration of nucleation and crystal growth by the small addition of transition metals to lithium disilicate glasses

Abstract

The addition of small amounts of niobium or tantalum oxide to lithium disilicate glass provokes a drastic decrease of the steady-state nucleation rates and the crystal growth velocities. The viscosity of the residual glassy matrix is considered as a function of the crystallization degree in the course of a non-isothermal crystallization. For simplification, a homogeneous distribution of the added oxides in the glass matrix is assumed. While the viscosity initially decreases, it significantly increases again for higher crystallization degrees hindering crystal growth. However, it was shown that the additives are enriched at the crystal interface. Several possible reasons for the inhibition of nucleation and growth kinetics such as viscosity, interfacial energy crystal/glassy phase, thermodynamic driving force or impingement rate are discussed. Since the crystallization front is blocked by the additives the impingement rate is decreased with increasing additive concentration. Since small concentrations of Nb2O5 and Ta2O5 have a drastic effect on the nucleation, these components should be enriched at the interface crystal/glass. This will only take place, if it leads to a decrease in the interfacial energy. Since this effect alone should result in an increase of the nucleation rate, it must be overcompensated by kinetic effects.

Donor–Acceptor Control in Grown‐in‐Glass Gallium Oxide Nanocrystals by Crystallization‐driven Heterovalent Doping

“…Different factors can affect the glass transition and the crystallization steps inside a complex glass. In fact, transition metal ions tend to gather at the NC growing front, forming a barrier to atomic diffusion during phase separation and NC growth, as recently demonstrated in doped lithium disilicate systems …”

“…Different factors can affect the glass transition and the crystallization steps inside ac omplex glass.I nf act, transition metal ions tend to gathera tt he NC growing front, formingabarrier to atomicd iffusion during phase separationa nd NC growth, as recently demonstrated in doped lithium disilicate systems. [45] In fact, in nanophases, it is thermodynamically unfavorable for the dopant to enter the NC. Therefore, dopant species are preferably excluded from the NC "bulk" and located on the nanoparticle surface.…”

“…Such effects were in fact observed in Er-doped SnO 2 NCs in glass, [44] and have been analyzed in ar ecent study on lithium disilicates with transition metal doping. [45] Therefore, the development of an ovel doping-induced strategy of DAP engineering in Ga oxide nanophases needs data-for now still unavailable-aboutt he possible effectso fd opant species on the NC growth.…”

Effects of d0 and s2 cations on optical properties of silicate glasses

“…However, the doping concentrations used in this study are below thresholds for crystallisation observed in other studies [258,259]. 0.10mol% Nb2O5 in lithium disilicate glass slightly decreases the steady state nucleation rate, resulting in fewer crystals developing relative to the base glass [259]. Crystals are unlikely to form in the glasses produced as the dopants are dilute, the glass was not heat treated, and soda lime silica glasses do not tend to crystallise without sufficient nucleation points (such as lithium disilicate [260]).…”

“…configurations have the propensity for crystal nucleation in glasses due to their large ionic radii, high charge density and predilection for clustering [129]. However, the doping concentrations used in this study are below thresholds for crystallisation observed in other studies [258,259]. 0.10mol% Nb2O5 in lithium disilicate glass slightly decreases the steady state nucleation rate, resulting in fewer crystals developing relative to the base glass [259].…”