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Abstract In borate materials, boron is found predominantly in either trigonal planar, or tetrahedral coordination states with oxygen, which are the two most ubiquitous building blocks of borate glasses. The fraction of tetrahedral boron,N₄, is found to vary considerably with both glass composition and applied pressure, as well as with fictive temperature – a result of its underlying dependence on temperature in the molten and supercooled liquid states. As such, the parameterN₄is of fundamental structural importance, along with the mechanisms driving its evolution and its strong influence on thermophysical material properties.N₄in glasses has been experimentally determined using a variety of means including nuclear magnetic resonance (NMR) spectroscopy, vibrational spectroscopy, and x-ray and neutron diffraction. In this review, we discuss how the techniques for the measurement ofN₄have evolved and improved since the pioneering x-ray diffraction measurements of the 1930s, up to the present day. A database is compiled of the availablehigh-qualitynumerical experimental data forN₄, with a non-exclusive focus on binary borate glasses of the formRM₂O_z–B₂O₃whereRis the molar ratio of modifier to boron oxide andMis a metal cation of formal chargez+, other than boron. In addition, we report newN₄values for a series of strontium borate glasses, measured by¹¹B magic angle spinning NMR, where a disparity in the literature is found. Based on the findings of the review, we are able to point to the gaps in our knowledge where future resources could best be focused, as well as summarizing overarching trends, the present state-of-the-art, and making recommendations for best practices. 

Abstract Previous research has shown a consistent discrepancy in the reported structure of alkaline earth aluminosilicate glasses using molecular dynamics (MD) simulations versus nuclear magnetic resonance (NMR) experiments. Past MD results have consistently shown less than 5% five‐coordinated Al units (Al^[5]) in peraluminous glass compositions, but with high fractions of triple‐bonded oxygens (TBO, i.e., triclusters). Experimental results have shown a high fraction of Al^[5]with no direct evidence for TBO. One of the main criticisms associated with high TBO content found in MD‐generated glass structures is the use of classical interatomic potentials. To investigate this issue, we analyze the formation of both TBO and Al^[5]using three independently developed potentials with varying silica content and [Al₂O₃]/[MgO] ratios for the magnesium aluminosilicate (MAS) system. We specifically choose compositions with high ratios of alumina to magnesium oxide as this region is not as commonly explored. Results indicate that Al^[5]charge compensates the Al network in metaluminous compositions (compositions with more Mg than Al) while both TBO and Al^[5]are prevalent in peraluminous ranges (high Al content compositions) to charge balance Al units. From the literature, NMR experiments report MAS glasses with varying Al^[5]fractions and show significant differences for the same reported compositions. When comparing MD results from this work, the fraction of calculated Al^[5]is within the experimental variation found in the literature. This indicates that classical potentials can accurately capture alumina environments and that both Al^[5]and TBO can coexist in relatively high fractions. From the consistency in our results, we conclude that TBOs are inherent to the aluminosilicate glass system and are not simulation artifacts. 

The optical functions of crystalline paratellurite (α-TeO2) and amorphous TeO2 were determined using several optical techniques: (1) standard spectroscopic two-modulator generalized ellipsometry (2-MGE) of paratellurite (200–850 nm, 6.2–1.46 eV), (2) near-normal-incidence two-modulator generalized ellipsometry microscopy (2-MGEM) of paratellurite (577 nm, 2.15 eV), (3) Mueller matrix transmission of paratellurite (320–798 nm, 3.87–1.55 eV), and (4) polarized transmission of paratellurite (323.6–334.3 nm, 3.83–3.71 eV). The 2-MGE measurements yielded highly accurate values of the dielectric functions and error estimates from 1.46 to 6.2 eV for both paratellurite and amorphous TeO2, whereas the polarization-dependent transmission yielded more accurate values of the absorption coefficient below the band edge of paratellurite. The 2-MGEM measured the diattenuation of paratellurite, which is related to the birefringence. Mueller matrix transmission measurements of paratellurite of a (001) cut crystal as a function of angle of incidence were used to determine both the birefringence and the rotary power as a function of photon energy. 

Glasses are typically characterized by time-dependent relaxation, leading to temporally changing properties. This inconsistency is a substantial issue in the development of new glasses, in particular optical glasses that require predictive responses to realize highly controlled and uniform optical responses. Here, we seek to expedite the relaxation rate using a novel thermo-ultrasonication process. As such, the As2S3 chalcogenide glass system is an ideal candidate due to its low glass-transition temperatures (Tg) and prevalent use as optical materials. The samples were subjected to ultrasonic vibration at an elevated temperature below Tg to accelerate their relaxation. We employ a combined theoretical–experimental approach to study glass relaxation via the evolution of refractive index and optical band edge. By understanding the effects of ultrasonication on glasses, we demonstrate new insights into the nature of relaxation while opening the possibility of developing ultra-stable glasses that can realize optical devices with increased lifespan. 

The Tenth Borate Conference on Glass, Crystals, and Melts (Borate X) was held in July 2023 in Corning, NY and it honuored Efstratios “Stratos” Kamitsos. He is the leading advocate for the use of infrared and Raman spectroscopy in the study of glasses, with borate glasses having received considerably more attention than other glassy systems. For forty years he made essential discoveries of atomic‐level structure using these techniques in conjunction with other spectroscopies. Here, we review his personal life and present a selective, non‐comprehensive summary of his scientific accomplishments and his role as a teacher, mentor, and friend. 

In this work, the transport path of potassium ions in potassium borate glass and structural units, NBO and cavity occupancy that affect the transport of potassium ions were analyzed in detail.