Understanding the structure, thermal, and optical properties in Al2O3-incorporated La2O3-TiO2-Nb2O5 glasses

Glasses in the 30La(2)O(3)-40TiO(2)-30Nb(2)O(5) system are known to have excellent optical properties such as refractive indices over 2.25 and wide transmittance within the visible to mid-infrared (MIR) region. However, titanoniobate glasses also tend to crystallize easily, significantly limiting their applications in optical glasses due to processing challenges. Therefore, the 30La(2)O(3)-40TiO(2)-(30-x) Nb2O5-xAl(2)O(3) (LTNA) glass system was successfully synthesized using a aerodynamic containerless technique, which improves glass thermal stability and expands the glass-forming region. The effects of Al2O3 on the structure, thermal, and optical properties of base composition glasses were investigated by XRD, DSC, NMR, Raman spectroscopy, and optical measurements. DSC results indicated that as the content of Al2O3 increased, the thermal stability of the glasses and glass-forming ability increased, as the 30La(2)O(3)-40TiO(2)-25Nb(2)O(5)-5Al(2)O(3) (Nb-Al-5) glass obtained the highest Delta T value (103.5 degrees C). Structural analysis indicates that the proportion of [AlO4] units increases gradually and participates in the glass network structure to increase connectivity, promoting more oxygen to become bridging oxygen and form [AlO4] tetrahedral linkages to [TiO5] and [NbO6] groups. The refractive index values of amorphous glasses remained above 2.1 upon Al2O3 substitution, and a transmittance exceeding 65% in the visible and mid-infrared range. The crystallization activation energies of 30La(2)O(3)-40TiO(2)-30Nb(2)O(5) (Nb-Al-0) and Nb-Al-5 glasses were calculated to be 611.7 and 561.4 kJ/mol, and the Avrami parameters are 5.28 and 4.96, respectively. These results are useful to design new optical glass with good thermal stability, high refractive index and low wavelength dispersion for optical applications such as lenses, endoscopes, mini size lasers, and optical couplers.