Andrei M. Efimov

IR fundamental spectra and structure of pyrophosphate glasses along the 2ZnO·P2O5–2Me2O·P2O5 join (Me being Na and Li)

The IR reflection spectra of mixed zinc alkali pyrophosphate glasses in the broad frequency ranges are reported and the quantitative treatment of these with a version of the dispersion analysis method was conducted based on the specific analytical model of the complex dielectric constant of glasses. Numerical data on the optical constants, band frequencies, and band intensities are calculated. Results obtained are interpreted in terms of vibrations of the (PO3)2− and (PO2)− terminal groups, (PO4)3− anion, and P–O–P bridge. The presence of all these groups in the structures of glasses under study is confirmed and the formation of the (P3O9)3− ring metaphosphate anion rather than the chain polymeric phosphate anions is suggested. The gradual decrease in the width of the anion distribution toward the pyrophoshate anion with the Me2O for ZnO substitution is also confirmed. It is shown that this decrease determines the IR spectrum variations observed in the 0 to about 27 mol% Na2O composition range. The amounts of the (PO4)3− and (P3O9)3− anions are shown to become negligible in the structures of glasses with Na2O content greater than 30 mol%, and the IR spectrum variations observed in the 27–45 mol% Na2O composition range are shown to be mostly due to the intensity redistribution from the low-frequency component of the asymmetric stretch of the (PO3)2− terminal group to the high-frequency component of the same stretch.

Vibrational spectra, related properties, and structure of inorganic glasses

Methods for the quantitative analysis of the IR and Raman spectra of various inorganic glasses to determine physically meaningful optical functions and individual band parameters are discussed. Available approaches to the problem of how to describe the mechanism of formation of the vibrational spectra of glasses (such as the quasi-molecular model, central force model and its recent refinements, and the model of phonon localization regions) are critically discussed. Recent data on band intensities and/or frequencies obtained with these methods for phosphate, borate, and germanate glasses are considered. Trends in the IR and Raman band assignments deduced from the current state of vibrational spectroscopy of glasses are analyzed and structural information obtained by different authors for binary phosphate, borate, and germanate glasses is compared. It is shown that, based on data on individual band parameters obtained, some related optical and dielectric properties of glasses in their transparency range can be calculated and/or modeled. Particular directions that are promising for further development of studies into vibrational spectroscopy of glasses are specified.

Quantitative IR spectroscopy: Applications to studying glass structure and properties

Abstract A review of data obtainable with various methods of quantitative treatment of the IR spectra of glasses is given. The version of the dispersion analysis method using a specific analytical model for the complex dielectric constant of glasses is shown to be the most appropriate tool for calculating the IR band parameters for glasses. Applications of data on band parameters are illustrated by examples for binary silicate, borate, and germanate glasses. Band parameter versus glass composition plots are discussed and the opportunity to calculate the ‘static’ dielectric constant corresponding to that characteristic of the ultra high frequency range is shown. The above model uses the convolution of the Lorentzian and Gaussian functions, where the parameters of the Gaussian function characterize the random frequency distributions of the near-zero-wavevector phonon intensities. The idea of such a distribution can be a basis for the semi-empirical calculation of the IR spectra of vitreous solids.

Water-related IR absorption spectra for some phosphate and silicate glasses

Abstract The water-related IR absorption spectra of some alkaline earth metaphosphate glasses, sodium silicate glasses, and window glass in the 1300–4000 cm−1 range are investigated. In the 1500–2600 cm−1 region, four strong bands are found for all glasses studied. These bands, based on a similarity in their locations to those reported earlier for pyrophosphate glasses, are assigned to different stretching vibrations of the hydroxyl group participating in the strong hydrogen bonding of a single kind. Slight variations in band locations depending on glass composition are shown. For silicate glasses, the peak absorptivities for the low-frequency hydroxyl-related bands around 1590, 1740 and 2100 cm−1 are found to be greater by ∼15, 15, and 4–5 times, respectively, than maximum absorptivities in the entire 2300–3700 cm−1 range. This rise in absorption with a decrease in wavenumber below 2300 cm−1 is considered to be the reason why literature sources available missed three above bands. A conclusion is made that Scholze’s scheme of formation of water-related IR spectra of glasses probably needs reconsidering.

Water-related IR absorption spectra for alkali zinc pyrophosphate glasses

Abstract The water-related first-order IR absorption spectra of zinc alkali pyrophosphate glasses in the 1400–4000 cm−1 range are investigated. These spectra are shown to contain much greater number of spectral features than the spectra of silicate glasses. The quantitative treatment of spectra obtained is conducted with the dispersion analysis version using the convolution analytical model for the complex dielectric constant. The water-related species in glasses under study are shown to be both the bound hydroxyl group participating in the hydrogen bonding and the H2O molecule. The corresponding spectral bands are resolved and their frequencies are compared to those in the spectra of water-containing crystals. The stretching mode of bound hydroxyl is shown to be split into a series of components in the 1600–3000 cm−1 range, which is interpreted in terms of the multi-site effect. The occurrence of the multi-site effect for the impurity-related mode is assumed to indicate the phonon-like nature of this mode and non-uniform distribution of the bound hydroxyl groups in the glass samples. The stretching modes of the H2O molecule are shown to result in several bands in the 2800–3500 cm−1 range.

Multi-site effect in the IR spectra of various inorganic glasses: experimental evidence and structural reasons

Data on the IR spectra of various glasses are reviewed and the spectra of glasses such as vitreous barium metaphosphate, alkali zinc pyrophosphate glasses, and binary borate glasses are subjected to an additional quantitative treatment. A multi-band pattern in the range of the asymmetric stretching modes is shown to occur in the spectra of these glasses. The main reason for the splitting of the asymmetric stretching modes of basic structural groups is shown to be a multi-site effect due to the occurrence of two or more translationally non-equivalent positions of structural groups in the regions of phonon localization. Investigation of the relative intensities of the spectral components originated from the same stretching mode as a function of glass composition is suggested as a possible tool for the study of subtle features of glass structures.

The IR spectra of non-oxide glasses of various types: Crucial differences and their origin

Abstract The reasons for dividing the IR spectra of various non-oxide glasses into two kinds are given. The spectra of the first kind exemplified by those of vitreous BeF2 and chalcogenide glasses, reveal, as in the case of the spectra of oxide glasses, a broad variety of stretching and bending modes; moreover, the multi-site effect similar to that known for oxide crystals adds complexity to the mode pattern. By comparison the IR spectra of heavy metal fluoride glasses are simple, thus being unlike the glass spectra of the first kind. Possible reasons that might be responsible for such a simplicity are discussed. The most probable reason is an overlapping of closely spaced spectral components related to different vibrations, which prevents resolution of these components.