Browsing by Author "Topper, Brian"

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    Anomalous Deformation Behavior in ULE Glass upon Microindentation: A Vibrational Spectroscopic Investigation in the Induced Structural Changes of a Ti-Silicate Glass
    (American Chemical Society, 2021-02) Möncke, Doris; Lind, Felix; Topper, Brian; Kamitsos, Efstratios I.
    Ultralow expansion (ULE) glass, a binary TiO2–SiO2 glass with 5.67 mol % TiO2, was exposed to microindentation. Vitreous silica was similarly treated and used as a reference material, including the characterization of mechanical properties by means of ultrasonic echography and nanoindentation. The structural modifications induced by indentation were analyzed by micro-Raman spectroscopy. The observed structural changes are consistent with an anomalous, densification-driven, deformation mechanism similar to those observed for vitreous silica or commercially relevant low alkali borosilicate glasses like Duran. As for these fully polymerized glasses, the Raman spectra of indents in the ULE glass are characterized by an upshift of the 407 cm–1 band and an increase in the intensity of the D1 and D2 defect bands, all consistent with structural rearrangements from mostly larger five- and six-member rings to a larger population of smaller four- and three-member rings and an overall lowering of the free volume in the glass. However, contrary to silicon, titanium may change its coordination number under the impact of microindentation. Raman spectra of selected reference materials such as TiO2 and BaTiO3, with known octahedral titanium coordination and known connectivity, as well as fresnoite Ba2TiSi2O8 with known fivefold Ti4+ coordination, are therefore included in this study in support of assigning the new activity appearing in the Raman spectra after an indentation of the ULE glass sample.
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    Glass as a State of Matter—The “newer” Glass Families from Organic, Metallic, Ionic to Non-silicate Oxide and Non-oxide Glasses
    (Mineralogical Society of America, 2022-05) Möncke, Doris; Topper, Brian; Clare, Alexis G.
    In theory, any molten material can form a glass when quenched fast enough. Most natural glasses are based on silicates and for thousands of years only alkali/alkaline earth silicate and lead-silicate glasses were prepared by humankind. After exploratory glass experiments by Lomonosov (18th ct) and Harcourt (19th ct), who introduced 20 more elements into glasses, it was Otto Schott who, in the years 1879–1881, melted his way through the periodic table of the elements so that Ernst Abbe could study all types of borate and phosphate glasses for their optical properties. This research also led to the development of the laboratory ware, low alkali borosilicate glasses. Today, not only can the glass former silicate be replaced, partially or fully, by other glass formers such as oxides of boron, phosphorous, tellurium or antimony, but also the oxygen anions can be substituted by fluorine or nitrogen. Chalcogens, the heavier ions in the group of oxygen in the periodic table (S, Se, Te), on their own or when paired with arsenic or germanium, can function as glass formers. Sulfate, nitrate, tungstate and acetate glasses lack the conventional anion and cation classification, as do metallic or organic glasses. The latter can occur naturally—amber predates anthropogenic glass manufacture by more than 200 million years. In this chapter, we are going to provide an overview of the different glass families, how the structure and properties of these different glass types differ from silicate glasses but also what similarities are dictated by the glassy state. Applications and technological aspects are discussed briefly for each glass family.
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    On the Structure of Lithium and Strontium Borate Glasses Modified with Yttrium and Rare-Earth Cations Investigated by Vibrational Spectroscopy
    (New York State College of Ceramics at Alfred University. Inamori School of Engineering., 2020-11) Topper, Brian; Möncke, Doris; Clare, Alexis; Misture, Scott; Kamitsos, Efstratios
    The thesis begins with a comprehensive review of the structure and properties of borate glasses. This is followed by a predominantly qualitative assessment of highly modified lithium and strontium borates containing yttrium and rare-earth oxide additions that have been prepared by the traditional melt-quenching technique. To the author's knowledge, reports on the ternary glasses studied here are not available in the literature. The feasibility of glass formation for these new compositions is discussed and the structures of the resulting materials have been studied, primarily, with vibrational spectroscopy as well as selectively with differential scanning calorimetry, X-Ray diffraction, and time-resolved fluorescence spectroscopy. Raman and Infrared spectroscopies suggest the glasses formed in the vicinity of the orthoborate stoichiometry are structurally similar to the high temperature phase of the related yttrium or rare-earth orthoborate crystals, regardless of whether the glass transition temperature lies above or below the corresponding phase transformation temperature. A relationship between the crystal phase transformation temperature and the glass transition temperature has been observed through the partial devitrification of borate melts containing relatively high yttrium content. That is, for glasses where the glass transition temperature is above the phase transformation temperature, only short-range order structural units akin to high temperature phase will be present in both the glass and any crystallization products. For glasses where the glass transition temperature is below the phase transformation temperature, the bulk glass is also made up of the short-range order structural units found in the high temperature phase; however, low temperature phase crystallites are detected with XRD. These crystallites, comprised only of tetrahedral orthoborate units arranged n B3O9^9- rings, are seen also as well-defined structures approximately 30 microns in diameter using confocal Raman microscopy. The addition of oxides with the high field strength trivalent yttrium ion to strontium borate glasses was found to depolymerize the borate network into ionic species while simultaneously increasing the glass transition temperature. In this series, the increase of the cation motion band frequency from 180 cm^-1 to 323 cm^-1 indicates the trivalent yttrium ions form stronger bonds with network oxygen than the divalent strontium ions. This correlates with the onset of the glass transition temperature increasing non-linearly from 630.7 °C to 652.2 °C for glasses containing 5 mol% and 25 mol% Y2O3, respectively. Lithium yttrium/rare-earth orthoborate glasses were found to consist solely of isolated trigonal borate units and to be insensitive to the use of either yttrium or other rare-earth elements, all of which have a well-known tetrahedral orthoborate crystalline phase. The absence of isomerization or disproportionation at the orthoborate stoichiometry implies the driving mechanism for glass formation in these glasses can be viewed as having a physical rather than chemical origin. This is to say, vitrification is dependent on the freezing-in of highly distorted, isolated trigonal borate structures - which are favored at high temperatures and in the melt compared to their tetrahedral counterpart. Several of the lithium yttrium/rare-earth orthoborate glasses were doped with Tb^3+ and the measured lifetime of the 543 nm emission using 375 nm excitation was ~2.2 ms. Measured lifetime decays, in conjunction with the relevant literature, suggest that even if trivalent rare-earth cations are present in small quantities, in a partially or fully depolymerized borate glass, the Tb^3+ ions will seek out local sites whose short range order corresponds to that of the high temperature crystalline phase. Indeed, this observation is in excellent agreement with the qualitative Raman interpretation of bulk strontium yttrium borate glasses where the introduction of the small quantities of Y2O3 is seen to induce the formation of trigonal orthoborate units below the pyroborate stoichiometry. Overall, the results obtained from the Tb^3+ doped orthoborate glasses here permit interpretation of previously unexplained published results. This is framed in the context of experimental and computational results pertaining to alkali and alkaline-earth borates that show that metal cations with high field strength will determine their local environment to a greater degree than metal cations present whose field strength is lower.