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- ItemRheological investigations in the decomposition ränge of the system Na₂O-B₂O₃-SiO₂(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Eberstein, Markus; Habeck, Andreas; Brückner, RolfThree glass melts from the Vycor-type widely distributed along the mixing gap of the pseudobinary line SiO₂-(B₂O₃:Na₂O = 84:16) were invesdgated each one with three different thermal histories. The following rheological properties were determined by the cylinder compression method: the Newtonian and non-Newtonian flow behaviour, the stress generadon modulus as a measure of the stiffness, the high-temperature tensile strength and the critical deformation rate at which the first crack appears. The influences of the fundamental glass compositions (SiO₂ content) as well as the thermal pretreatments on these properties are demonstrated and discussed on the basis of isochomal conditions (equal Newtonian viscosities). The results can be interpreted by means of the knowledge about the demixing rules and processes which lead to various rheological two-phase Systems. Most drastical changes of the rheological properties are observed in the middle of the mixing gap where spinodal decomposidon has its optimum and where he differentation between the matrix phase and decomposed phase is lost.
- ItemDevelopment of high-permittivity glasses for microwave LTCC tapes(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Eberstein, Markus; Schiller Wolfgang A.One of today's leading packaging concepts in microelectronics and microsystems is the technology of Low Temperature Cofiring Ceramics (LTCC). It is based on ceramic tapes that sinter at low temperatures (< 950 °C) and are capable of fine-line wiring by use of high-conductivity metals, preferably silver ( ϑm = 961 °C). To lower sintering temperatures of crystalline powders, glass powder is added. Depending on the amount of glass added, two mechanisms of sintering are possible: reactive or nonreactive liquid phase sintering. Reactive sintering requires small amounts (< 10 vol.%) of a very low softening glass (ϑsoft < 400°C). If the glass amount is increased to more than 50 vol.%, nonreactive sintering occurs in the glass softening range. According to the microstructure observed for each case, the respective types of materials are called Glass Bonded Ceramics (GBC) and Glass Ceramic Composites (GCC). Integration of microwave filters in LTCC multilayers requires inner dielectric layers with medium, temperature-stable permittivities (εr = 30 to 60) and low dielectric loss (tan δ < 2 ∙ 10^-3). Up to now, appropriate materials have been realized only by GBC sintering at 900 °C and above. Hence, pure silver metallization is not possible. To overcome this limitation, GCC are a promising way. Therefore, crystalline substances possessing εr of about 100 and low dielectric loss - for example Ba(La, Nd)2Ti4O12 - were combined with special high-permittivity glasses. Α development of such glasses is presented in this work. Addition of oxides of easily polarizable elements (e. g. Nb2O5, La2O3 , TiO2 ) effects an increase in permittivity of selected basis compositions from the systems BaO-Al2O3-B2O3-SiO2 (εr up to 15) and La2O3-Ba2O3-TiO2 (εr up to 20). GCC mixtures made of 65 vol.% of these glasses and 35 vol.% BaLa2Ti4O12 showing microwave properties and sintering temperatures below 900 °C are introduced.
- ItemStructural relaxation phenomena in silicate glasses modified by irradiation with femtosecond laser pulses(London : Nature Publishing Group, 2017) Seuthe, Thomas; Mermillod-Blondin, Alexandre; Grehn, Moritz; Bonse, Jörn; Wondraczek, Lothar; Eberstein, MarkusStructural relaxation phenomena in binary and multicomponent lithium silicate glasses were studied upon irradiation with femtosecond (fs) laser pulses (800 nm central wavelength, 130 fs pulse duration) and subsequent thermal annealing experiments. Depending on the annealing temperature, micro-Raman spectroscopy analyses evidenced different relaxation behaviours, associated to bridging and non-bridging oxygen structures present in the glass network. The results indicate that the mobility of lithium ions is an important factor during the glass modification with fs-laser pulses. Quantitative phase contrast imaging (spatial light interference microscopy) revealed that these fs-laser induced structural modifications are closely related to local changes in the refractive index of the material. The results establish a promising strategy for tailoring fs-laser sensitivity of glasses through structural mobility.