Browsing by Author "Kashchieva E."

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    Synthesis of doped bismuth titanate ceramics with Nd2O3 and SiO2 and their electrical properties
    (2013-05-21) Slavov S.; Krapchanska M.; Kashchieva E.; Parvanov S.; Dimitriev Y.
    Bismuth-titanate ceramics containing SiO2 and Nd2O3 as additives are synthesized by melt quenching method in the system Bi2O3-TiO2-Nd2O3-SiO2 at temperature range 1260 - 1500oC. The phase composition of the obtained materials is determined by X-ray diffraction analysis and energy dispersive spectroscopy. Using scanning electron microscopy different microstructures are observed in the samples depending on the composition. The addition of SiO2 and Nd2O3 allows controlling the crystallization, glass formation ability, melting temperature and Curie temperature. Different values of conductivity, dielectric losses and relative permittivity are obtained depending on the composition. Measurements of the electrical conductivity, capacitance and dielectric losses of selected samples are performed by DC resistible bridge and digital capacity meter (with frequency of 1 kHz) using two-terminal method and a suitable sample holder with graphite electrodes. It is established that all investigated samples are dielectric materials with conductivity between 10-9 and 10-13 (O cm)-1 at room temperature, dielectric permittivity from 1000 to 3000 and dielectric losses tgd between 0,0002 and 0,1.
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    The effect of Nd substitution on the glass forming ability and thermal properties in the system Bi2O3-TiO2-SiO2
    (2015-01-01) Slavov S.; Kashchieva E.; Parvanov S.; Dimitriev Y.
    The paper reports data on glass formation in wider concentration ranges. The samples amorphous nature is characterized by x-ray diffraction analysis, their thermal characteristics and stability are determined by differential thermal analysis (DTA), while the transmission and absorption characteristics outlined are investigated by ultraviolet-visible spectroscopy (UV-Vis). SiO2 content increase leads to a shift of the absorption border to lower wavelengths. The experimental results show that it is possible to obtain low-melting glasses containing 5 mol % - 20 mol % SiO2 and 30 mol % - 63 mol % Bi2O3 with the synthesis technique applied. Substitution of Bi2O3 with Nd2O3 up to 10 mol% leads to the preparation of a complex multicomponent glasses and glass-crystalline materials of high thermal stability.