Browsing by Author "Tasheva T."

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    Correlation between thermal expansion coefficient and interionic interaction parameter in ZnOBi2O3B2O3 glasses
    (2018-01-01) Komatsu T.; Inoue T.; Tasheva T.; Honma T.; Dimitrov V.
    The volume thermal expansion coefficients (β) in 50300°C of xZnOyBi2O3zB2O3 glasses (x = 1065, y = 1050, z = 2560 mol%) were measured and the refractive index-based interionic interaction parameters A(no) were estimated from oxide ion electronic polarizabilities to acquire deeper insight into the relationship between the electronic polarizability and chemical bonding state of oxide glasses. The glasses have relatively large values of c = 210289.© 1017K11, and the substitution of ZnO for B2O3 and the increase in Bi2O3 content result in an increase in c. The values of A(no) decrease with the substitution of ZnO for B2O3 and the substitution of Bi2O3 for ZnO. An almost linear correlation was observed between c and A(no), i.e., the volume thermal expansion coefficient decreases with increases in the interionic interaction parameter. A good correlation was also observed between A(no) and the refractive index-based optical basicity a(no). The interionic interaction parameter is helpful for understanding the chemical bonding state of oxide glasses.
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    Group optical basicity and single bond strength of lead borate glasses
    (2018-01-01) Dimitrov V.; Tasheva T.; Komatsu T.
    Equation providing the calculation of the theoretical optical basicity Λth(1) of PbO-B2O3 glasses is suggested taking into account the contribution of the mole fraction and the group basicity of different structural units, namely BO3 and BO4 groups. It is found that in case of PbO-B2O3 glasses the curves of the refractive index based optical basicity Λ(n0) and the theoretical optical basicity Λth(1) as a function of PbO content follow a similar trend changing their slope at about 50 mol. % PbO. An equation is proposed to calculate the average single bond strength BM-O of PbO containing borate glasses taking into account the mole fractions of PbO3, PbO4, PbO6, BO3 and BO4 groups. It is established that both equations give the possibility for more precisely estimation of the theoretical optical basicity and the single bond strength of the glasses. It is found that the single bond strength of PbO-B2O3 glasses decreases with increasing PbO content. The observed increase of the optical basicity with decreasing single bond strength of lead borate glasses is discussed with increase the number of Pb-O-B and Pb-O-Pb bonds containing oxide ions with increased polarizability.
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    Group optical basicity and single bond strength of oxide glasses
    (2018-01-01) Dimitrov V.; Komatsu T.; Tasheva T.
    This paper is a review of our recent results in the field of group optical basicity of the oxide glasses. Dimitrov and Komatsu have recently introduced the concept of group (i.e. microscopic) optical basicity, proposed by Duffy and Ingram, to binary R2O (RO) - TeO2 (R = Na, Mg, Sr, Ba, Zn and Pb) and ternary 10R2O.10R'O.80TeO2 (R = Li, Na and K, R'= Mg, Ba and Zn) tellurite glasses based on N4 and N3 fractions of different Te4 and TeO3 groups. In fact, the group basicity of Te4 unit with one non-bridging oxygen (λTeO4 l - = 1.23), Te4 unit without non-bridging oxygen (λTeO4 l = 0.99) and a terminal TeO3 unit with two non-bridging oxygens (λTeO3 l - = 0.82) is evaluated. Equations for evaluation of the theoretical optical basicity Λth(1) of Na2O-B2O3, PbO-B2O3, Na2O-SiO2 and R2ORO- TeO2 glasses are advanced taking into account the contribution of the mole fraction and the group basicity of different structural units, namely BO3, BO4 and SiO4 groups. Equations providing the calculation of the average single bond strength BM-Oof Na2O-B2O3, PbO-B2O3B2O3, Na2OGeO 2, Bi2O3-B2O3 and ZnO-Bi2O3-B2O3 glasses are suggested considering the mole fractions of BO3, B4, Ge4, GeO6, PbO3, Pb4 and PbO6 groups. It is established that there is a general trend of optical basicity increase along with single bond strength decrease in borate-silicate-germanate-tellurite-bismuthate glasses sequence.
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    OPTICAL PROPERTIES AND CHEMICAL BONDING OF TiO2-BaO-V2O5 GLASSES
    (2016-01-01) Tasheva T.; Dimitrov V.
    Glasses of compositions xTiO2.(35-x)BaO.65V2O5 (x=0, 1, 3, 5, 10, 15 and 20 mol %) are prepared using the conventional melt quenching method. XRD, DTA and DSC analysis are performed. The XRD results confirm the amorphous nature of the samples. The ternary glasses show low glass transition temperatures, Tg, of 228°C - 253°C and crystallization temperatures, Tx, of 266°C - 323°C. The density measured decreases with increase of TiO2 content from 3.542 g cm-3 to 3.287 g cm-3. The theoretical refractive index, the electronic oxide ion polarizability, the optical basicity and the optical band gap of the glasses are calculated by the Lorentz-Lorenz equation. The glasses are found to possess a high refractive index (2.169 - 2.236), a comparatively narrow band gap (4.01 eV - 3.67 eV), high electronic ion polarizability (2.650 Å3 - 2.722 Å3) and high optical basicity (1.040 - 1.057). The third order nonlinear optical susceptibility χ(3) is determined by the generalized Miller’s rule and the three photon model. It is found that χ(3) values are in the 0.76 - 1.1 x10-12 esu range. The average single bond strength BM-O and the interaction parameter A(no) are calculated. The bond strength is found to vary from 253 kJ mol-1 to 285 kJ mol-1, while the interaction parameter is in the 0.050 Å-3 - 0.055 Å-3 range, thus suggesting the presence of weak chemical bonds. The presence of such bonds, namely Ba…O=V, V-NBO (nonbridging oxygen), V-O-Ti and V-O-V is verified by the glasses IR-spectra. The high polarizability of the oxide ions in these bonds accounts for the observed linear and nonlinear optical properties of the glasses. A structural model of glasses containing VO5, VO4 and TiO4 groups is advanced.
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    Optical properties and structure of B2O3 - BaO - V2O5 glasses
    (2015-01-01) Tasheva T.; Dimitrov V.
    Glasses with compositions xB2O3.(35-x)BaO.65V2O5 (x = 1, 3, 5, 7, 10, 15 mol %) were prepared using a conventional melt quenching method. DTA and DSC analysis were performed. The theoretical refractive index, electronic oxide ion polarizability, optical basicity and optical band gap of the glasses were calculated by Lolrentz-Lorenz equation. The glasses were found to possess high refractive index (2.48 - 2.54), narrow band gap (2.54 - 2.71 eV), high oxide ion polarizability (2.41 - 2.70 Å3) and high optical basicity (1 - 1.05). The third order nonlinear optical susceptibility χ(3) was determined by generalized Miller's rule. It was established that χ(3) is close to the experimental value of 1.1x10-11 esu measured for thin film of V2O5 by Hashimoto et al. using THG method. The average single bond strength BM-O and interaction parameter A(no) were calculated. The bond strength was found to vary from 255 kJ mol-1 to 305 kJ/mol and interaction parameter was in the 0.05-0.07 Å-3 range, thus suggesting the presence of weak chemical bonds. Such bonds, namely Ba...O=V, V-NBO (nonbridging oxygen), V-O-B and V-O-V were confirmed by IR-spectra of the glasses. The high polarizability of the oxide ions in these bonds accounted for the observed linear and nonlinear optical properties of the glasses. A structural model of glasses containing BO3, B2O5, VO5 and VO4 groups is proposed.
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    PHYSICOCHEMICAL AND STRUCTURAL CHARACTERIZATION OF SILICATE GLASSES CONTAINING IRON OXIDES
    (2023-01-01) Mihailova I.; Harizanova R.; Tasheva T.; Dimova N.; Rüssel C.
    The interest in glasses containing iron oxides is determined by the possibility for application in optics, sensors, nanoelectronics, biotechnology and medicine. Subject of the present investigation is the preparation of glasses in the system 16Na2O/10CaO/(74-x)SiO2/xFe2O3, x = 0, 5, 10 and 15 mol % by applying the traditional melt-quenching technique. X-ray diffraction analysis proves that the materials with up to 15 mol % Fe2O3 are amorphous while for higher concentrations, the crystallization of magnetite and hematite occurs during melt quenching. For the physicochemical characterization of the glasses, the density, molar volume and oxygen packing density have been determined. The Becke line method has been utilized for the refractive indices measurement. The structural evolution in dependence of the Fe2O3 concentration has been studied by Fourier Transformed Infrared Spectroscopy. The data obtained from the different methods correlates well and reveals a depolymerization tendency of the silicate network with the increasing Fe2O3 concentration, i.e. an increase in the number of SiO4 tetrahedra with more non-bridging oxygens as a result of the occurrence of Fe-containing polyhedra in the glass structure.
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    POLARIZABILITY APPROACH, STRUCTURE, AND NONLINEAR OPTICAL CHARACTERISTICS OF TELLURITE GLASSES IN THE V2O5-BaO-TeO2 SYSTEM
    (2021-01-01) Tasheva T.; Dimitrov V.
    Tellurite glasses with compositions xV2O5 - (35-x) BaO - 65TeO2 (where x = 5 mol %, 10 mol %, 15 mol %, 20 mol %, 25 mol % and 30 mol %) were melted using a conventional melt-quenching method. The polarizability approach was applied to the glasses. The glasses were characterized by both high electronic polarizability and optical basicity. The chemical bonding of the glasses was determined by estimating the interionic parameter and the single bond strength. The obtained values of these parameters were relatively low, which indicates the presence of weak chemical bonds in the glass structure. Such bonds, Te-O-Te, Te-O-V V-O-V andBa...O=Vwere confirmed by the IR spectra of the glasses. The nonlinear optical susceptibility was predicted by Miller's rule. The results indicate that the glasses are potential good candidates for applications in nonlinear optics.
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    Synthesis, optical properties and structure of NiO-BaO-V2O5 glasses
    (2017-01-01) Tasheva T.; Dimitrov V.
    Glasses with compositions xNiO.(35-x)BaO.65V2O5 (x= 1, 3, 5, 7, 10, 15 and 20 mol %) are prepared using a conventional melt quenching method. XRD and DTA/DSC analysis are performed. The results of XRD analysis confirm the amorphous nature of the samples. The glasses possess low glass transition temperature Tg of 267 - 282 A and crystallization temperature of 301 - 390°C The measured density decreases with increasing of NiO content from 3.560 to 3.490 g cm-3. The refractive index n0, optical band gap Eg, electronic oxide ion polarizability αO-2 and optical basicity Λ of the glasses are calculated by Lorentz-Lorenz equation. The glasses were found to possess high refractive index (2.174 - 2.271), narrow band gap (3.51 - 3.98 eV), high oxide ion polarizability (2.653 - 2.723 Å3) and high optical basicity (1.041 - 1.057). The third order nonlinear optical susceptibility χ(3) is determined by generalized Miller's rule and three photon model. It was established that χ(3) is high in the 0.78 - 1,43x10-12 esu range. The average single bond strength BM-O and the interaction parameter A(n0) are calculated. The bond strength is found to vary from 252 - 258 kJ mol-1 and the interaction parameter was in the 0.050 - 0.055 Å-3 range, thus suggesting the presence of weak chemical bonds. The structure of the glasses was investigated by means of IR spectroscopy. The analysis of IR spectra confirmed the presence of weak chemical bonds such as Ni-O-V, Ba...O=V, V-NBO (nonbridging oxygen) and V-O-V. The high polarizability of the oxide ions in these bonds accounts for the observed linear and nonlinear optical properties of the glasses.
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    SYNTHESIS, POLARIZABILITY APPROACH AND STRUCTURE OF TeO2-BaO-V2O5GLASSES
    (2020-01-01) Tasheva T.; Dimitrov V.
    Glasses with compositions xTeO2 - (35-x) BaO - 65V2O5 (where x = 5, 10, 15, 20, 25 and 30 mol %) were prepared using a conventional melt quenching method. Densities of the glasses at room temperature were determined with the Archimedes method. The theoretical linear refractive index and optical band gap of the glasses were calculated by the Lorentz-Lorenz equation. The glasses possess high refractive index (2.16 - 2.19) and comparatively narrow band gap (3.9 - 4.1 eV). The third order nonlinear optical susceptibility χ(3) was determined by generalized Miller’s rule. It was established that χ(3) equal to 0.72 - 0.85x10-12 esu is close to the experimental value of ~10-12 esu measured for pure TeO2 glass and TeO2 containing glasses by other authors using THG method. The refractive index and third order nonlinear optical susceptibility decrease and band gap increases with increasing TeO2 content. The average single bond strength BM-O and the interaction parameter A of the glasses were calculated. It was shown that BM-O is in the 258 - 295 kJ/mol range and A is in the 0.050 - 0.055 À-3 range suggesting for the presence of week chemical bonds. VO5, VO4 and TeO3 structural units were confirmed by the IR spectra and structural models of the glasses containing Ba…O-V, V-O-V and V-O-Te bonds were proposed. The oxide ions in these bonds possess high polarizability giving main contribution to the high values of linear and nonlinear optical properties of the glasses