Browsing by Author "Pernikov M."

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    IR-SPECTROSCOPY, THERMOPHYSICAL AND MECHANICAL PROPERTIES OF GLASSES IN THE SYSTEM Na2O/BaO/TiO2/B2O3/SiO2/Al2O3
    (2023-01-01) Harizanova R.; Gaydarov V.; Gugov I.; Zamfirova G.; Mihailova I.; Pernikov M.; Rüssel C.
    Glasses with the compositions (23.1-x)Na2O/23.1BaO/23TiO2/9.8B2O3/21SiO2/xAl2O3 x = 3, 7, 11 and 15 mol% were melted using a traditional melt-quenching technique. The thermophysical properties of the obtained glasses, i.e., glass transition temperature, Tg, and crystallization peak maximum temperature, Tc, were determined by differential scanning calorimetry and showed that the increasing alumina concentration leads to an increase of both the Tg and Tc values, while the difference Tg-Tc, used as a glass stability criterium, changes in the opposite manner, being highest for the glass with 3 mol % Al2O3 and smallest for the composition with 15 mol % Al2O3. The structure of the prepared series of glasses was studied by infrared spectroscopy and showed that the main structural units present are isolated and interconnected SiO4 tetrahedra. Both BO4 and BO3 structural units, which number initially increases with the increasing alumina concentration and then starts to decrease, are also present. The conducted depth-sensing indentation on the obtained glasses allowed to determine mechanical properties such as universal (HMV) and indentation (Hit) hardness, elastic modulus and elastic part of indentation work. The change of the Na2O/Al2O3 ratio resulted in increasing HMV and Hit up to 11 mol% Al2O3 and then a slight decrease of the respective parameters was observed.
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    PHASE COMPOSITION AND MICROSTRUCTURE CHARACTERIZATION OF STRONTIUM-MODIFIED BARIUM TITANATE GLASS-CERAMICS
    (2023-01-01) Harizanova R.; Pernikov M.; Mihailova I.; Tatchev D.; Avdeev G.; Avramova I.; Rüssel C.
    Dielectric glass-ceramic materials find various applications as parts of sensors, electronic components and even in biomedicine. The present work reports on the synthesis of glass-ceramic materials in the complex oxide system (23.1-z)Na2O/17.1BaO/6SrO/23TiO2/17.4SiO2/7.6B2O3/5.8Fe2O3/zAl2O3, z = 0 and 3 mol %. The melts show spontaneous crystallization during quenching. The phase composition is studied using X-ray diffraction and reveals crystallization of Ba1-xSrxTiO3 solid solutions with varying Ba/Sr ratio. The valence states and the local environments of the Ba, Ti and Fe ions of the prepared materials are investigated by utilizing X-ray photoelectron spectroscopy. It is shown that all the elements in the composition are present in their oxidized states and the formation of barium titanate based compounds is possible. The microstructure of the obtained samples is imaged by scanning electron microscopy and shows bright polygon-like crystalline structures embedded in a dark amorphous matrix. The further evaluation of the microstructure as average crystal size and volume fraction of the precipitated crystals is done by using microcomputed tomography. Thus, a relatively high crystalline volume fraction is observed for the samples without alumina. The samples with alumina possess comparable as size and volume fraction crystals.