Vesselin Dimitrov

Electronic oxide polarizability and optical basicity of simple oxides. I

The average electronic oxide polarizability α02− of numerous single component oxides has been calculated on the basis of two different properties: linear refractive index n0 and energy gap Eg, which have demonstrated remarkable correlation. The optical basicity Λ of the oxides has been estimated on the basis of average electronic oxide polarizability calculated from the refractive index Λ(n0) and the energy gap Λ(Eg). A good agreement has been observed between the optical basicity data obtained using independent initial quantities. The simple oxides have been separated into three groups according to the values of their oxide polarizability. The α02− values (above 3 A) obtained for PbO, Sb2O3, and Bi2O3 have been attributed to the high cation polarizability and the presence of a lone pair in the valence shell of the cation.

IR spectra and structure of V2O5GeO2Bi2O3 glasses

This paper reports a study of the structure V2O5GeO2Bi2O3 glasses by IR spectroscopy to obtain information about the competitive role of each of V2O5, GeO2 and Bi2O3 in the formation of the glass network. The amorphous samples were obtained by the twin-roller technique. Bi2O3 leads to transformation of the layered and chain vanadate structure and depolymerization of three-dimensional germanate lattice. The bismuthate complexes can be viewed as deformed BiO6 groups. It is established that with a decrease in the V2O5 content VO4 groups are formed. GeO4 structural unit with different degrees of polymerization arer present in the network in the entire concentration range.

Linear and nonlinear optical properties of simple oxides. II

A suitable relationship between the linear refractive index n0, the energy gap Eg, and the nonlinear refractive index n2 has been looked for on the basis of experimental and theoretical data reported in the literature for numerous simple oxides. It has been established that the nonlinear refractive index increases with increasing linear refractive index and decreasing energy gap of the oxides. This is related to the increasing metallicity of the oxides. Oxides with a high nonlinear refractive index posses a metallization criterion of approximately 0.30–0.45.

Glass formation and structure of glasses in the V2O5MoO3Bi2O3 system

The glass formation region in the V2O5MoO3Bi2O3 system was investigated by the roller-quenching method. Low melting glasses were obtained in the MoO3- and V2O5-rich compositions. Characterization of the glasses was made by X-ray diffraction, differential thermal analysis (DTA) and IR spectroscopy. According to the DTA data, the glass transformation temperature, Tg, for the different compositions varied between 200 and 290°C and the cystallization temperature, TX, was within the interval of 225–330°C. Structural models for glasses of th MoO3Bi2O3 and V2O5Bi2O3 systems were suggested on the basis of IR spectral investigations, by comparing with known crystalline structures. It was shown that the glasses possess [MoO4], [MoO6], [VO4], and [BiO6] groups as basic structural units.

Glass formation and structure in the V2O5Bi2O3Fe2O3 glasses

Abstract Glass formation V2O5Bi2O3Fe2O3 system was investigated by the roller-quenching method and low melting V2O5- and Bi2O3-rich glasses were obtained. Glasses were characterized by X-ray diffraction, differential thermal analysis (DTA), IR and Mossbauer spectroscopy. The glass transformation temperature, Tg, varied between 270 and 442°C, and the crystallization temperature, Tx, was in the range of 342–550°C. Structural models for glasses of the V2O5Bi2O3Fe2O3 system are suggested on the basis of IR and Mossbauer spectral investigations. It was shown that the glasses posses [VO5], [VO4], [BiO6], [FeO6] and [FeO4] groups as basic structural units.

Glass formation and structure in the system MoO3–Bi2O3–Fe2O3

Abstract The glass formation region in the MoO 3 –Bi 2 O 3 –Fe 2 O 3 system was investigated by the roller-quenching method. Glasses melted at temperatures 3 -rich compositions. Analysis of the glasses was made by X-ray diffraction, differential thermal analysis (DTA), infra-red spectroscopy (IR), and Mossbauer spectroscopy. According to the DTA data, the glass transformation temperature, T g , for the different compositions varies between 360°C and 440°C and the crystallization temperature, T x , is in the range 390–470°C. Structural model for the glasses are suggested on the basis of IR and Mossbauer spectral data. In the region of MoO 3 rich compositions, the network forming units MoO 6 are connected by Mo–O–Mo bridging bonds. The presence of Me 2 O 3 (Me=Bi, Fe) leads to transformation of MoO 6 to MoO 4 . Thus, in a wide region of compositions the glass network has a scheelite-like structure containing isolated MoO 4 structural units which are surrounded by MeO 6 groups.

Structure of glasses in PbO-V2O5 system☆

Abstract Structural models for glasses of the PbO-V2O5 system in 0–75 mol% PbO range are discussed. On the basis of IR-spectral investigations by comparing with known crystalline structure of V2O5, PbV2O6 and Pb2V2O7, it is shown that the basic structural units in glasses in this composition range are unaffected VO5 groups (a band at 1020 cm−1), affected VO5 groups (bands at 970-950 cm−1), V2O7 pyrovanadate units (bands at 860 cm−1 and 780 cm−1) and VO4 isolated tetrahedra (a band at 760 cm−1).

Electronic polarizability, optical basicity, and interaction parameter of La2O3 and related glasses

The electronic polarizability and optical basicity of La2O3 and related glasses have been determined from ultraviolet absorption spectra and calculations based on the Lorentz–Lorenz equation. The optical basicity for La2O3 oxide is found to be 1.07, being much larger compared with typical glass-forming oxides such as B2O3 (0.42) and SiO2 (0.48) but being similar to heavy element oxides such as TeO2 (0.93). The Yamashita and Kurosawa’s interaction parameter of La2O3 is 0.03 A−3, indicating that La2O3 is classified as a normal ionic (basic) oxide, i.e., an ionic bonding character in the La3+–O bond is proposed. Close correlations are confirmed among optical basicity, interaction parameter, and oxygen 1s binding energy in x-ray photoelectron (XPS) spectra for La2O3–P2O5 and other La2O3-containing glasses. It is found from XPS and Raman spectra that La3+ ions in La2O3–P2O5 glasses act as network modifiers, supporting an ionic bonding character in the La3+–O bond. The parameters related to electronic polarizab...

The structure of vitreous V2O5-TeO2

Abstract A high resolution neutron diffraction study of a sample of vitreous V2O5–TeO2, containing 5 mol% V2O5, has been performed using the LAD time-of-flight diffractometer at the ISIS spallation pulsed neutron source. Reciprocal space data were obtained to high scattering vectors, Q, and have been Fourier transformed to yield the real space correlation function, T(r). The first neighbour Te–O and O–O peaks in T(r) have been investigated using peak fitting techniques which suggest the presence of both TeO3 and TeO4 units. The shortest Te–O bond length is 1.91 A, with two further contributions at 2.10 and 2.17 A, while the average O–O distance within the TeOn structural units is 2.76 A. A comparison with the crystalline polymorphs of TeO2 indicates that the structure of the glass is nearer to α-TeO2 than to β-TeO2. The results from the present study are compared to earlier neutron diffraction data for a V2O5–TeO2 glass containing 10.2 mol% V2O5. Fourier transform infrared spectra have been recorded for a series of three V2O5–TeO2 glasses over the range 400–1000 cm−1 and analysed using deconvolution techniques. The results obtained are in good agreement with the neutron data, particularly in respect of the existence of TeO3 and TeO4 structural units.

Structure of V2O5MoO3Fe2O3 glasses

Abstract Infrared spectra have been examined in V2O5MoO3Fe2O3 glasses, and the results were compared with infrared spectra of known crystals. This study has shown that structural units formed in the glasses include [VO5] groups (bands at 1020-930 cm−1), isolated [VO4] and [MoO4] tetrahedra (a band at 840 cm−1), [FeO4] tetrahedra and [FeO6] octahedra (bands at 660 cm− and 520-480 cm−1). Glass formation is discussed on the basis of glass structure. This study has established that the appearance of isolated tetrahedral groups in the network without MOM bridging bonds decreases the glass-formation ability.