The study describes the role of specific oxide species in the structure and development of special glass

A study carried out at the Center for Research, Education and Technology in Vitreous Materials (CeRTEV) in São Carlos, in the state of São Paulo, Brazil, shows for the first time that including niobium oxide (Nb₂O₅) in silicate glass results in silica network polymerization, which increases bond density and cohesion, increasing the mechanical and thermal strength of special glass.

The study is described in an article published in the journal Materials Journal.

The first author of the article, Henrik Bradtmüller, is a postdoctoral researcher at the Federal University of São Carlos’s Center for Exact Sciences and Technology (CCET-UFSCar). His supervisor is Edgar Dutra Zanotto, director of CeRTEV and the last author of the article. CeRTEV is hosted by UFSCar.

“Our study combined experimental observations using nuclear magnetic resonance spectroscopy and Raman spectroscopy with computer modeling. Apart from the mentioned results, we found that high levels of niobium lead to Nb₂O₅aggregation, and high electronic polarizability, which has a significant effect on the properties of the glass,” says Bradtmüller.

It is worth remembering that Raman spectroscopy provides accurate information on the molecular structure of materials, while nuclear magnetic resonance (NMR) spectroscopy examines the magnetic properties of their atomic nuclei.

“Our strategy based on these two observational techniques and computational modeling can be used to study the functional properties of many other types of glass, including optical materials, active glass and fast glass conductors. This will help the development of well-organized glasses for different applications,” said Bradtmüller.

Alongside the everyday use of ordinary glass in containers, windows and so on, high-quality glass is also almost everywhere in today’s world, says Bradtmüller. It is present in microscopes and telescopes used by scientists, for example, in optical fibers used to carry data and energy, and in glass-ceramic orthotic devices used extensively in medicine. “Recognizing the role that glass plays in modern society, the United Nations declared 2022 the International Year of Glass,” he said.

Using advanced technology, materials scientists use machine learning software and other computational tools to design glass with tailored properties, but to do so they need reliable databases and structural parameters that take into account the physicochemical complexity of glass.

This is the significance of the research by Bradtmüller and colleagues. “Glass intermediate oxides play an important role in this new technological moment. They do not form glass under standard cooling in the laboratory, but they can make a positive contribution before other oxides by helping to build oxygen bridges and giving the glass interesting properties. Niobium oxide is a good example ,” he explained.

Glass containing niobium (Nb) is valued for its non-linear optical properties, as well as potential applications in optoelectrical devices, and mechanical properties related to organic production. “Although studies have been conducted using Nb₂O₅ before us, the structural role of Nb remained unclear, due to the lack of systematic data of spectroscopic properties. We intend to fill this knowledge gap in our study,” he said.

“We found through spectroscopy that the addition of Nb causes the ‘polymerization’ of the silica-oxygen network, increasing the cohesion of the glass components. This explained the role of Nb as a ‘pre-network’. Another highlight of the research is our demonstration that the new technique of NMR that we developed in 2020 using other active materials in glass. This method, called W-RESPDOR, can be used to measure the distance between two elements – in this case, lithium and Nb, which has such a challenging nucleus that did not measured in similar ways.”

The simulation model showed that lithium ions are randomly distributed in the silica-based glass at the nanometric scale (5-10 nanometers), while Nb tends to form clusters in high Nb areas.₂O₅he explained, adding that this type of structural arrangement has not been described in the literature and is the first contribution to the study.

“From a broader perspective, the study points to an experimental and computational strategy to investigate the role played in glass by intermediate oxides with active nuclei for NMR spectroscopy,” Zanotto said.