Aluminosilicate glasses are ubiquitous in high-performance displays due to their favorable thermal, mechanical, and optical properties. They also exhibit interesting structural features depending on the ratio of alumina to modifiers in the glass system. Excess modifiers exist in the metaluminous region, while the peraluminous region contains more negatively charged alumina structures than modifiers. As the composition switches from metaluminous to peraluminous, anomalous changes in properties such as the glass transition temperature, viscosity, and refractive index occur. This has been explained with two contrasting structural transformations to accommodate the lack of charge-balancing modifiers: either aluminum increases in coordination (forming five-coordinated or six-coordinated Al) and/or oxygens become three-coordinated (known as triclusters). The precise charge-balancing mechanism remains a subject of much debate in the community. This review highlights this structural debate by providing a chronological understanding of how these two theories evolved. We also summarize the state-of-the-art understanding of the aluminosilicate glass structure. By gaining a more comprehensive view of the two opposing structural views within the aluminosilicate glass system, we can gain insights on valuable future research from both experimental and modeling perspectives.
Calcium aluminosilicate glasses have technological importance for a variety of industrial applications. However, the short-range structure of this glass system remains widely debated regarding the formation of oxygen triclusters. It is argued that triclusters are observed in high percentages within molecular dynamics simulations because of the high melting temperatures and correspondingly high fictive temperatures. This work explores the formation of such structural units by first simulating various compositions at different liquid temperatures to understand thermodynamic factors affecting the formation of such species. Structural results are then implemented into a statistical mechanical model which can predict the formation of triclusters at a given fictive temperature. Results show temperature and composition dependence of these structures, with aluminum charge modification favored in the peraluminous regime. It is concluded that oxygen triclusters are the preferred method of charge compensation even when extrapolating to laboratory fictive temperatures, indicating that triclusters are not a byproduct of simulation timescales.
Tin oxide gas sensor can detect various gases by using the conductivity changes due to adsorption and desorption processes of gaseous molecules on its surface. The reduction of the power consumption especially for batteries back-up operation, is one of the challenge for SnO2 gas sensors. We propose a new solution using a silicon oxynitride membrane (SiOxNy) to reach this objective. Thin films of SiOxNy with different compositions have been studied. Their composition, residual stress, Young modulus and mechanical strength have been evaluated. As a result, we propose an optimized silicon oxynitride membrane with a low residual stress (-50 MPa), giving above 95% fabrication yield and low power consumption (65 mW / 450°C). A new sensors generation has been successfully fabricated and its mechanical strength and thermal performances have been evaluated. Moreover, an equation is derived, which describes the variation of the Young modulus as a function of the silicon oxynitride composition.
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