Study On Preparation And Properties Of Novel Large-Size Lanthanum-Titanium Optical Glasses With High Refraction

La₂O₃-TiO₂ glasses prepared by containerless technology have broad application prospects in high-performance lenses,optical communication,AR/VR lenses and other fields because of their high refractive index,good thermal stability and excellent mechanical properties.However,it is difficult to prepare large-size La₂O₃-TiO₂ glasses due to the limitation of glass formation ability and containerless technology,which severely limits their applications.In this study,the network-forming Ge O₂ is introduced to effectively improve the glass-forming ability,which enables the preparation of large-size Ge O₂-La₂O₃-TiO₂（GLT）glasses by conventional melt fast cooling method.In this thsis,large GLT glasses were successfully prepared by the melt fast cooling method,and Nb/Zr was introduced separately to further optimize the optical,thermal,and structural properties of the glasses.The study of GLT ternary system glass found that the refractive index of GLT glass increases with the content of TiO₂ up to 2.07 and the Abbe number reaches 21.82,which is a more excellent high refractive and low dispersion glass.The additive nature of the refractive index of the glass is verified,and TiO₂ can be used as an important component to enhance the refractive index in optical glasses.However,the glass formation ability,thermal stability and density decrease with the increase of TiO₂ content,and its transition temperature T_g andΔT（Difference between the onset of crystallization and the glass transition temperature）are greater than 833°C and 209°C,respectively,with good stability against precipitation.The glass network structure and valence bond composition in the GLT system were analyzed by combining XRD,Raman spectroscopy and photoelectron spectroscopy.It was found that the glass network contains[TiO₄],[TiO₅]and[TiO₆]clusters of TiO₂,and the[TiO₅]polyhedral structure gives higher densities to the glass network as the TiO₂ content increases.The doping of Nb₂O₅ in the Ge O₂-La₂O₃-TiO₂ system can effectively improve its refractive index,with a maximum refractive index of 2.16.Nb₂O₅ can also substantially improve the anti-precipitation properties of the glass and lower its glass transition temperature,with aΔT of 239.2°C and a T_g reduction of 22.9°C when the Nb₂O₅content is 6 mol%.With the addition of Nb₂O₅,the larger oxygen atom ratio induces the transformation of[TiO₅]polyhedra into[TiO₆]octahedra,and the more dense structure is an important factor for the improvement of refractive index and mechanical properties.The hydroxyl absorption coefficient of the glass can be effectively reduced and the Ti coloring can be weakened by drumming in dry oxygen,and the hydroxyl absorption coefficient is reduced from 3.11 cm^-1 to 1.81 cm^-1 with a maximum transmittance of 86.3%in the visible wavelength band.Adding Zr O₂ to Ge O₂-La₂O₃-TiO₂ can improve the refractive index,hardness and acid and alkali corrosion resistance.The refractive index of the Ge O₂-La₂O₃-TiO₂system is 2.12 at the maximum,and the component also achieves an ultra-highΔT of243.0°C,which has excellent stability against precipitation.The addition of Zr O₂ into GLT system can form[Zr O_n]polyhedron in the glass network,supplement free oxygen and promote the entry of La³⁺ions into the glass network to enhance the glass density.The maximum hardness is 8.02 GPa,and the mass loss ratio is very small under acid and alkali corrosion conditions,and the alkali resistance is stronger than the acid resistance.The damage mechanism of GLTZ glass in compression experiments was determined by combining the acoustic emission signal parameters and wavelet transform decomposition results,and the glass failed and then fractured by the combined effect of micro cracks sprouting at the defect site and converging into larger cracks.This thesis systematically investigates the properties of GLT ternary system high refractive index glasses and the effects of doping with Nb/Zr on the optical and thermal properties,stability and their structures of GLT system glasses,and understands their fracture failure mechanisms through compression acoustic emission experiments.The excellent properties of the three system glass materials demonstrate the promising applications in the fields of optical devices,optical communication and decorative materials.