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

Abstract

Glasses in the 30La2O3‐40TiO2‐30Nb2O5 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 30La2O3‐40TiO2‐(30−x) Nb2O5‐xAl2O3 (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 30La2O3‐40TiO2‐25Nb2O5‐5Al2O3 (Nb‐Al‐5) glass obtained the highest ΔT value (103.5°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 30La2O3‐40TiO2‐30Nb2O5 (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.

High‐refraction index glasses with ultra‐high Young's modulus and high hardness fabricated by containerless processing

“…α O 2− initially increased then decreased, and the overall trend is decreasing. As shown in Equation (), the refraction index is determined not only by α O 2− but also by V m , the V m for high‐entropy glass RE = La, Tm, and Lu decrease from 40.26 to 39.67, suggesting that the effect of V m is greater than α O 2− 16,25 …”

“…These are larger than those of SiO 2 (68.8 kJ/cm 3 ) and B 2 O 3 (86.0 kJ/cm 3 ) 7 . In addition, it has been reported that high field ions can induce the transformation of Al 3+ into a higher coordination number 8,13,16 . In aluminosilicate glasses, which typically range from 3% to 30% and from 1% to 2%, respectively, 17 these high‐entropy glasses reach values near 41.9% and 14.0% 8 .…”

“…In the mid‐infrared range, the transmittance of high‐entropy glass exhibits an absorption peak at 3000 nm, attributed to the absorption caused by OH − groups in the glass. The absorption coefficient caused by OH − can be calculated using the following equation 16 : $$$$\begin{equation}{\mathrm{\;}}{\alpha _{{\mathrm{O}}{{\mathrm{H}}^ - }}} = \frac{{\ln \left( {{T_{\mathrm{m}}} / T} \right)}}{\sigma }\;\end{equation}$$$$Here, α OH − is the absorption coefficient, T m is the maximum transmittance in the IR region, and T is the transmittance at 3000 nm, σ is the thickness of the sample. The calculated absorption coefficient of OH − for RE = La is 0.52 cm −1 , which is similar to La 2 O 3 ‐Ga 2 O 3 ‐Ta 2 O 5 glass (0.52 cm −1 ) 18 .…”

“…7 In addition, it has been reported that high field ions can induce the transformation of Al 3+ into a higher coordination number. 8,13,16 In aluminosilicate glasses, which typically range from 3% to 30% and from 1% to 2%, respectively, 17 these high-entropy glasses reach values near 41.9% and 14.0%. 8 This efficiently enhances the Young's modulus and hardness of the glasses.…”

“…As shown in Equation (11), the refraction index is determined not only by α O 2− but also by V m , the V m for highentropy glass RE = La, Tm, and Lu decrease from 40.26 to 39.67, suggesting that the effect of V m is greater than α O 2− . 16,25 According to the single oscillator model from the Drude-Voigt relationship, the refractive index is expressed as a function of the wavelength by the following formula 4,20,26,27 :…”