Structural modification associated with Al₂O₃ addition in oxyfluoride glasses: Thermal and mechanical properties

Abstract

In this work, the effect of gradual addition of Al2O3 substituting SiO2 on the structural, thermal, and mechanical properties of SiO2–BaF2–K2O–GdF3–Sb2O3‐based oxyfluoride glasses have been studied. The X‐ray diffraction (XRD) patterns and differential scanning calorimetric (DSC) curves indicate that there is a distinct primary crystallization corresponding to BaGdF5 phase formation in the samples without (0AlG) and with 5 mol% substitution of Al2O3 (5AlG) while the sample with 10 mol% of Al2O3 (10AlG) does not show such crystallization event. Further, the activation energy (Ea) for fluoride crystal formation is higher for the 5AlG in comparison to the 0AlG glass as determined by Kissinger, Augis‐Bennett and Ozawa models. Fourier transform infrared (FTIR) and Raman spectroscopy analysis confirmed the structural modification with the gradual addition of Al2O3 in the glass matrix revealing dominant presence of AlO4 tetrahedral units in 10AlG sample unlike in 5AlG sample which exhibited the manifestation of AlO6 units. Such structural variation has further been substantiated from the estimated elastic properties like Young's modulus (E), shear modulus (G), bulk modulus (K), longitudinal modulus (L), and mean ultrasonic velocity (Um) by showing a decrease for 5AlG sample in comparison with 0AlG sample followed by subsequent increase for 10AlG sample.

Thermal and crystallization behavior of SiO2‐PbF2 glass system in the presence of ErF3 and Al2O3

“…Also, the glass thermal stability factor ( T x − T g ) was improved with increasing Al 2 O 3 content. This latter effect originates from the role of alumina in the strengthening of the network bonds via increasing network connectivity . Heat treatment of Er 3+ ‐doped samples was done at T x .…”

“…Hence, this highly viscous layer around the crystallites controls crystal growth mechanism. This layer acts as a diffusion barrier layer restricting crystallite size to a nanometric range and controlling particle size distribution through decreasing crystal growth velocity …”

“…Furthermore, because of high thermal instability and abrupt crystallization during the melt‐pouring process, achieving transparent glass with high concentration of rare‐earth ions is almost impossible in this system . It seems that alumina content plays a key role in liquid‐liquid phase separation mechanism, crystallization process and thermal stability of oxyfluoride glass‐ceramics, which can bring antidevitrifying properties and improve optical performance of rare‐earth‐doped oxyfluoride glass‐ceramics . Thus, it is necessary to find out the effect of alumina on oxyfluoride glass compositions and clarify some conjectures about Al 2 O 3 as an effective intermediate component.…”