L. Konstantinov

Vibrational spectra of ETS-4 and ETS-10

Raman and i.r. absorption spectra of ETS-4 and ETS-10 were measured at room temperature in the frequency range 200–1,400 cm −1 . The peaks observed in the spectra were identified through model calculations of the internal modes of vibration for clusters typical of the structure of these materials.

Vibrational spectra of rings in silicate glasses

Isotropic, HH and HV Raman as well as infrared spectra of isolated n-membered rings (n = 3, 4, 5, 6, 7) of ideal silicon-oxygen tetrahedra are calculated. The dependences of the spectral line frequencies and intensities on the number of tetrahedra in the ring as well as on the type and the degree of structural disorder are studied. The results show that the ring order influences the mode localization, thus changing the spectral line positions and intensities, while the structural disorder (ring puckering and topology) affects mainly the vibrations of the bridging oxygen atoms changing the frequencies and intensities of the peaks corresponding to the modes localized in this type of atom. The effect of the surrounding matrix upon vibrational properties of the rings is briefly discussed and a better, but by no means full, agreement with experiment is obtained by taking into account this effect.

Adhesivity of molecular sieve films on metal substrates

Films of silicalite-1, zeolite Y, and SAPO-5 were deposited on steel and copper substrates. The film adhesivity, thermal stability, and morphology of the zeolite films were studied. It is shown that the main factors determining the zeolite film mechanical properties are the interactions at the substrate-gel interface. On the other hand, the mechanism of film formation depends on the type of the initial gel and the substrate surface activity. In addition, the results obtained indicate that the substrate plastic deformation, i.e., the high density of substrate surface defects, is one of the dominant parameters for good film adhesivity and thermal stability.

Influence of metal substrate properties on the kinetics of zeolite film formation

The primary stages of zeolite Y and silicalite-1 film formation on both untreated and plastically deformed copper substrates are considered from the viewpoint of the film growth kinetics and morphology. Experimental results indicate a satisfactory agreement between the kinetic and profilometric data.

Degree of structural disorder in sodium metasilicate glass: model for Raman spectra

Abstract The mid- and high-frequency bands in the Raman spectrum of the alkali metasilicate glass Na 2 O · SiO 2 above 500 cm −1 are interpreted by modelling the effects of SiOSi bridging angle, OSiO tetrahedral angle, dihedral angle and bond lengths disorder using Monte Carlo simulations and second order perturbation theory for the averaged Greens function. It is demonstrated that the Raman peaks are broadened by different structural mechanisms with FWHMs depending, in the first approximation, linearly on the degree of structural disorder. A combined fit of the experimentally observed FWHMs yields values for the relative degree of structural disorder corresponding to 16° SiOSi disorder, 9° OSiO disorder and 3.6% disorder in all the SiO bond lengths, in good agreement with previous molecular dynamics results.

Comparison of physicochemical properties of zorite and ETS-4

On the basis of X-ray diffraction, Raman and IR spectroscopy and TG/DTA analysis a comparative study of zorite and its synthetic titanium silicate analogue ETS-4 was performed. It is shown that the observed differences between ETS-4 and zorite are due to the differing chemical compositions of these materials and to the isomorphous substitutions in zorite.

Chemical composition and vibrational spectra of tungsten-bearing goethite and hematite from Western Rhodopes, Bulgaria

The incorporation of tungsten in goethite and hematite as well as the relationships between the two minerals in a supergene environment are considered on the basis of a representative sample from the Grantcharitza tungsten deposit (Western Rhodopes, Bulgaria), studied by scanning electron microscopy, electron probe microanalysis, X-ray powder diffraction and micro-Raman spectroscopy. The sample is a colloform black material consisting predominantly of goethite ( G-I ) with 6.83–10.85 wt.% WO3 and of several products of its alteration, including W-poor goethite ( G-II ) with 1.35–5.72 wt.% WO3, a W-rich ferric iron oxide phase ( Fw ) with 22.19–25.12 wt.% WO3, and hematite ( H-I ) with 1.21–1.72 wt.% WO3. It is shown that G-I is an aggregate of proper goethite and of a W-rich ferric iron oxide phase ( Sw ). The alteration of G-I aggregates includes: (i) selective dissolution of Sw which either re-precipitates, thus forming a separate W-rich phase ( Fw ), or which is almost entirely removed from the aggregate; (ii) replacement of the residual goethite G-II by hematite H-I . An atomic ratio W/Fe of about 0.006 is supposed to correspond to the isomorphic (Fe3+ ⟷ W6+) incorporation of tungsten into goethite and hematite in the sample studied. The Raman spectrum of G-II resembles the already published spectroscopic data on goethite, whereas H-II shows spectral features typical of a highly disordered hematite structure. The presence of W atoms in the structures of hematite H-I and goethite G-II causes the appearance of a low-frequency shoulder of the Raman peak near 400 cm−1. According to the Raman spectroscopy data, the W-rich constituent Sw in G-I aggregates as well as its re-precipitated variety Fw both have a Fe-O network similar to that of goethite. In both materials only a small amount of W atoms occupies Fe-positions, while the major part of tungsten forms W-O self-assembled clusters generating a broad band between 580 and 750 cm−1 in the Raman spectra. As shown by model calculations, tungsten is organised in chain-like clusters of corner-sharing WO6 octahedra with an average W-O-W bond angle of about 150°. In addition, Fw contains isolated WO6 octahedra or corner-sharing-WO6 clusters with an average W-O-W angle of about 180°.

Influence of Non-Tetrahedral Cations on Si–O Vibrations in Complex Silicates

The effect of non-tetrahedral cations on the silicon–oxygen vibrational modes in complex silicates was modelled in a small-cluster approximation by introducing a shell containing first- and second-order neighbours of the peripheral oxygen atoms of the Si—O cluster. As an example, the proposed method was applied to study the Raman spectra of different types of tourmaline, which contain in their structure single six-membered rings of SiO4 tetrahedra. It is shown that in the range 450–750 cm−1 the Raman spectrum of the ring is sensitive to the type of cations in octahedral Y-positions and as a result the peaks shift and their shape modifies. Using such changes, one can estimate the occupation of Y positions in tourmalines by various cations.

Effect of doping on Raman spectra of Bi12SiO20

Abstract The effect of doping of Bi12SiO20 with various ions on the Raman spectra is investigated. It is shown that the dopants modify in a different way the structure of BSO.

Raman spectroscopic study of Mn-doped Bi4Ge3O12

Abstract Raman spectra of pure and Mn-doped Bi4Ge3O12 crystals are measured and the observed peaks are assigned through calculating the vibrational modes of different clusters representative for the Bi4Ge3O12 structure. The doping with Mn affects only the polar modes and the resulting changes in the spectra can be explained by anisotropic embedding of Mn into the host lattice of Bi4Ge3O12 which leads to an increase in the anisotropy of the long-range interatomic interactions.