Evolution from transparent SiO₂ glass to ceramics enabled by cold sintering with a transient chemistry: H₂SiO₃

Silica (SiO₂) glass has a wide range of industrial applications due to its outstanding optical, physicochemical, and electrical properties. Herein, a transparent SiO₂ glass with a high relative density of 96.8% is fabricated at 200 °C by cold sintering with a transient chemistry of H₂SiO₃, and a visible light transmittance of ∼80%, Vickers hardness of 3.1 (±0.14) GPa and Young's modulus of 45.6 (±2.7) GPa are achieved. Moreover, it is found that the transition from glass phase to crystallized ceramic occurs between 200 ^oC and 300 °C during the cold sintering process. The microstructural analysis shows an obvious phenomenon of recrystallization, accompanying by a formation of polygonal α-quartz grains of ∼150 nm. Meanwhile, the α-quartz ceramic presents an enhanced Vickers hardness and Young's modulus of 5.7 (± 0.13) and 60.2 (± 3.2) GPa, respectively. This work provides an efficacious way for designing SiO₂ glass and ceramics at low sintering temperatures.