New insight into the plastic deformation mechanisms during the SiO₂ phase transition process

The removal of lattice impurities is the key to the purification of high-purity quartz (HPQ), especially for the intracell lattice impurities. Generally, the intracell lattice impurities can be migrated to the quartz surface via roasting, then removed by acid leaching. In order to reveal the phase transition of quartz during the roasting process, the evolution of structure, bond length, volume, lattice parameter and lattice stress in original, Ti⁴⁺, Al³⁺/Li⁺ and 4H⁺ substituted SiO₂ phases were employed to investigate the mechanisms of plastic deformation based on density functional theory calculations. Results showed that the evolution of bond lengths and volumes were mainly dominated by phase transition, and the interstitial volume in high temperature SiO₂ phases was higher than that in low temperature, indicating that the phase transition from α-quartz to β-cristobalite was beneficial to the migration of interstitial impurities. In addition, the phase transition from α-quartz to β-cristobalite needs to overcome the energy barriers while the phase transition from α-cristobalite to β-cristobalite needs to overcome the lattice stress. This study therefore provides an excellent theoretical basis for the plastic deformation mechanism, for the first time, beneficial to understanding the removal mechanisms of lattice impurities.