Raman study of Pb5(GeO4) (VO4)2 crystals (original) (raw)
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Structure of lead germanate glasses by Raman spectroscopy
Journal of Non-crystalline Solids, 2001
Lead germanate glasses of the xPbO(1 À x)GeO 2 compositions with x ranging from 0.200 to 0.625 have been synthesised and their crystallisation behaviour and vibrational properties studied by dierential thermal analysis (DTA) and Raman spectroscopy. Raman spectra of the Pb 5 Ge 3 O 11 ceramics also have been measured and compared to lead germanate glass spectra and literature data on b-PbO. Ge atoms in low lead glasses are supposed to be surrounded by four to six oxygen atoms, while the high-lead glass (x 0X625) corresponding to stoichiometry of the Pb 5 Ge 3 O 11 ferroelectrics contains predominantly fourfold coordinated germanium. Structural resemblence of high-lead germanate glasses to the Pb 5 Ge 3 O 11 crystal is proposed rather than to b-PbO. The`boson' peak range in the spectra of lead germanate glasses is discussed taking into account the similarities of the spectra of glassy and crystalline Pb 5 Ge 3 O 11 . Ó
Isomorphic substitution in vanadinite [Pb5(VO4)3Cl]?a Raman spectroscopic study
Journal of Raman Spectroscopy, 2003
The Raman and infrared spectra of vanadinite [Pb5(VO4)3Cl] specimens from three localities were studied. Raman spectra were found to be both orientation and temperature dependent. Measurement of the Raman spectra at liquid nitrogen temperature allowed better band separation and increased the intensities of weak bands, thus permitting band assignment. Two types of isomorphous substitution were identified: (a) substitution in the bulk of the crystal where electron beam microanalysis identifies the presence of calcium and copper and (b) surface substitution where infrared spectroscopy shows the isomorphous substitution of vanadate by phosphate and of chloride by hydroxyl groups.
Raman and Infrared Vibrational Spectra of PbGa2S4 Crystal
Raman scattering spectrain different geometries at temperatures 10 - 300 K and infrared vibrational spectra in polarizations E||c and E⊥c for range 50 - 4000 cm-1 at 300 K were investigated for PbGa2Se crystals. Contours of reflection spectra in polarizations E||c and E⊥c were calculated and parameters of phonons and dielectric constants were determined. Temperature dependences of Raman spectra were investigated and soft modes with different temperature dependences in intervals 80 - 150 and 150 - 370 K were discovered. A group of lines attributed to Davydovmultiplets was found out and their polarization dependences temperature changes were investigated. Effective ion charges were calculated and a polarizability of ionic charges of Pb, Ga and S in PbGa 2S4 lattice was determined
Raman and optical reflection spectra of germanate and silicate glasses
Journal of Non-Crystalline Solids, 2005
Germanate and phosphosilicate glasses made in oxygen surplus conditions were studied by Raman and optical reflection methods. We found that the optical reflection spectra of the germanate glasses are quite similar to the one those of a GeO 2 crystal with the a-quartz structure. The reflection of phosphosilicate glasses is very close to silica glass-related spectra. Hence, the determining influence of the tetrahedral structure on reflection spectra is revealed. The Raman spectra of germanate samples are similar to those reported the one known in the literature. Octahedral entities, namely bands similar to stishovite vibration modes, were difficult to detect in phosphosilicate glasses through Raman spectroscopy.
Vibrational spectra and structure of alkali germanate glasses
Journal of Non-Crystalline Solids, 2001
Numerous structural studies have been carried out so far to elucidate the nature of the so-called germanate anomaly, but the correct structural model is still unknown. The objective of the present paper is to shed further light on the structure of alkali germanate glasses, namely those containing sodium and cesium oxides. Two series of glass samples were prepared, having molar compositions 100 À xGeO 2 Á xM 2 O (M Na and 0 6 x 6 35, or M Cs and 0 6 x 6 25). Polarized Raman and infrared absorption spectra were recorded for these glasses, as a function of the alkali content; infrared re¯ectivity measurements were also carried out and Kramers±Kronig analysis of the near-normal incidence spectra were compared with the polarized Raman spectra of the glasses. An overall structural picture has emerged, which is compatible with the presence of a fraction of higher coordinated Ge atoms, either ®ve-fold or six-fold. Ó
Journal of Raman Spectroscopy, 2006
Both Raman and infrared spectroscopy have been used to characterise the three phase-related minerals-dreyerite (tetragonal BiVO 4), pucherite (orthorhombic BiVO 4) and clinobisvanite (monoclinic BiVO 4)-and a comparison of the spectra is made with that of the minerals namibite (Cu(BiO 2)VO 4 (OH)), schumacherite (Bi 3 O(OH)(VO 4) 2) and pottsite (PbBiH(VO 4) 2 •2H 2 O). Pucherite, clinobisvanite and namibite are characterised by VO 4 stretching vibrations at 872, 824 and 846 cm −1. The Raman spectrum of dreyerite shows complexity in the 750 to 950 cm −1 region with two intense bands at 836 and 790 cm −1 assigned to the symmetric and antisymmetric VO 4 modes. The minerals schumacherite and pottsite are characterised by bands at 846 and 874 cm −1. In both the infrared and Raman, spectra bands are observed in the 1000-1100 cm −1 region which are attributed to the antisymmetric stretching modes. The Raman spectra of the low wavenumber region are complex. Bands are identified in the 328 to 370 cm −1 region and in the 404 to 498 cm −1 region and are assigned to the n 2 and n 4 bending modes. The minerals namibite and schumacherite are characterised by intense bands at 3514 and 3589 cm −1 assigned to the symmetric stretching vibrations of the OH units. Importantly, Raman spectroscopy enables new insights into the chemistry of these bismuth vanadate minerals. Raman spectroscopy enables the identification of the bismuth vanadate minerals in mineral matrices where paragenetic relationships exist between the minerals.
Raman spectra of silicate garnets
Physics and Chemistry of Minerals, 1998
The single-crystal polarized Raman spectra of four natural silicate garnets with compositions close to end-members almandine, grossular, andradite, and uvarovite, and two synthetic end-members spessartine and pyrope, were measured, along with the powder spectra of synthetic pyrope-grossular and almandine-spessartine solid solutions. Mode assignments were made based on a comparison of the different end-member garnet spectra and, in the case of pyrope, based on measurements made on additional crystals synthesized with 26 Mg. A general order of mode frequencies, i.e. R(SiO 4 )bT(metal cation)bT(SiO 4 ), is observed, which should also hold for most orthosilicates. The main factors controlling the changes in mode frequencies as a function of composition are intracrystalline pressure (i.e. oxygen-oxygen repulsion) for the internal SiO 4 -vibrational modes and kinematic coupling of vibrations for the external modes. Low frequency vibrations of the X-site cations reflect their weak bonding and dynamic disorder in the large dodecahedral site, especially in the case of pyrope. Two mode behavior is observed for X-site cation vibrations along the pyrope-grossular binary, but not along the almandine-spessartine join.