Disclosing crystal nucleation mechanism in lithium disilicate glass through molecular dynamics simulations and free-energy calculations

Abstract

Unraveling detailed mechanism of crystal nucleation from amorphous materials is challenging for both experimental and theoretical approaches. In this study, we have examined two methods to understand the initial stage of crystal precipitation from lithium disilicate glasses using molecular dynamics simulations. One of the methods is a modified exploring method to find structurally similar crystalline clusters in the glass models, enabling us to find three different embryos, such as Li2Si2O5 (LS2), Li2SiO3 (LS) and Li3PO4 (LP), in the 33Li2O·66SiO2·1P2O5 glass (LS2P1), in which P2O5 is added as a nucleating agent. Interestingly, LS2 and LP crystals were found inside the LS2P1 glass while LS crystal appeared on the glass surface, which agrees with experimental observations. The other method is free energy calculation using a subnano-scale spherical crystal embedded in the glass model. This method, which we called Free-Energy Seeding Method (FESM), allows us to evaluate free energy change as a function of crystal radius and to identify critical size of the crystal precipitation. The free energy profiles for LS and LS2 crystal nuclei in the LS2 glass models possess maximum energy at a critical radius as expected by classical nucleation theory. Furthermore, the critical radius and the energy barrier height agree well with recent experimental investigation, proving the applicability of this method to design glass–ceramics by atomistic modeling.

Microstructure and Mechanical Properties of Li2Si2O5 Whisker-Reinforced Glass-Ceramics

“…In this study, phase separation was promoted during the crystallization heat treatment to form Li-rich and Si-rich phases, after the addition of P 2 O 5 to the Li 2 Si 2 O 5 glass system. Li 2 O interacts with P 2 O 5 in the Li-rich regions to form Li 3 PO 4 crystal nuclei, which can occur at non-uniform nucleation sites of Li 2 SiO 3 and Li 2 Si 2 O 5 crystals according to the following reaction scheme, which was conducive to reducing the nucleation energy (Wen et al, 2007;Lodesani et al, 2020 Upon increasing the amount of Li 2 Si 2 O 5 whiskers, the whisker content in the Li-rich regions also increased. The added Li 2 Si 2 O 5 whiskers could act as nuclei sites, so the simultaneous effect of surface nucleation from the glass powders and that induced by the whiskers increased the degree of crystallization (Zhao et al, 2021).…”

Steering Interzeolite Conversion with Alkali Metal Cations: Lithium Maximizes Al Proximity in SSZ-13 Zeolite Genesis

“…XRD spectra (Figure (left)) confirm the presence of a layered lithium silicate Li 2 Si 2 O 5 in the synthesis output, increasing the Si content of the bulk output, which is not a pure zeolite anymore. This material consists of single layers of silica tetrahedra, each of which is connected to three other silica tetrahedra . The fourth corner of the tetrahedron is occupied by a Si–O – Li + species, all of which are pointed toward the interplanar void (Figure S2).…”

“…This material consists of single layers of silica tetrahedra, each of which is connected to three other silica tetrahedra. 55 The fourth corner of the tetrahedron is occupied by a Si−O − Li + species, all of which are pointed toward the interplanar void (Figure S2). This material has no (micro)porosity, hence the reduction in uptake of N 2 .…”

Study of Lithium Disilicate Based Nano Glass Ceramics Containing P2O5

“…The band at 787 cm -1 is due to Si motion in oxygen cage [31]. The band around 947 cm -1 corresponds to Q 2 units as well as the vibrations of the P-O bonds and the band centered around 1069 cm -1 corresponds to Q 3 units [18,[31][32][33][34]. For the glasses containing P2O5 ≤ 0.5 mol % the band around 1069 cm -1 is dominant which indicates that all the glasses mainly consist of Q 3 structural units.…”