Crystallization and nanostructure of transparent gel-derived KTiOPO4/SiO2 nano-glass–ceramics

The crystallization behavior and nonstructural evolution upon anneal of transparent gel-derived x(K2O–2TiO2–P2O5)–(100 − x)SiO2 (10 ⩽ x < 100) amorphous solids are systematically investigated for the first time. KTiOPO4 (KTP) nanocrystals are precipitated in a rather wide composition range (10 ⩽ x < 100) in the temperature range of 580–1000 °C. Nanophase separation on the length scales of 0.5–2 nm has been observed in the amorphous solids. The mean nanocrystal size is in the range of 20–200 nm depending on annealing temperature and isothermal dwell time. KTiOPO4 nanocrystals show a self-limited crystal growth and are stabilized from 20 to 50 nm in the annealing temperature range of 580–850 °C, while an abnormal crystal growth has been observed at higher temperatures. An amorphous phase separation–crystallization–growth mechanism is proposed in KTP/SiO2 nano-glass–ceramics. The apparent decrease in optical transmittance is mainly assigned to the growth of the nanopores and refractive index difference between KTP crystal and SiO2 glass. Based on these data, rational processing conditions can be designed for transparent KTiOPO4/SiO2 nanophase glass–ceramics, which meet the requirements for both the precipitation of the KTP and transparency of the glass–ceramics for SHG application.