A. Rulmont

Vibrational spectra of metaborates with infinite chain structure: LiBO2, CaB2O4, SrB2O4

The vibrational spectra (i.r. and Raman) of chain metaborates (LiBO2, CaBO2O4, SrB2O4) containing only condensed BO3 groups has been investigated by group theoretical methods and isotopic substitutions. The spectra are discussed in relation to the structure and possible coupling between the chains in the unit cell.

Vibrational spectrum of nasicon-like, rhombohedral orthophosphates MIMIV2(PO4)3

Abstract The Raman and i.r. spectra of nasicon-type M I M IV 2 (PO 4 ) 3 rhombohedral phosphates (M I = Li, Na, K, Rb, Cs, Tl; M IV = Ge, Sn, Ti, Zr, Hf) exhibit intricate relationships between the spectra and the chemical composition. The pattern of the PO 4 stretching frequencies is more or less strongly modified by the nature of both M IV and M I cations. Still greater variations are observed in the medium and low frequency region, although some external modes have been identified by the study of mass effects ( 6 Li 7 Li, 70 Ge 76 Ge, ZrHf etc.). The origin of this complex behaviour is discussed in relation to the structure.

Structural characterisation of glassy phases in the system Na2O–Al2O3–P2O5 by MAS and solution NMR, EXAFS and vibrational spectroscopy

The structure of sodium aluminophosphate glasses with a fixed O/P ratio of 4 and 3.5 has been investigated. For the monophosphate compositions, the phosphate network is completely depolymerised so that the glassy network is built through the aluminium atoms which are distributed on three different sites but lying mainly in tetrahedral coordination. 31P Magic angle spinning (MAS)-NMR spectra show the existence of three different cationic environments for the PO43− ions. In the glasses with the diphosphate compositions, we observed the disproportionation of some diphosphate groups into monophosphate and triphosphate ions crosslinked by the aluminium atoms whose average coordination increases. The diphosphate groups give a typical vibrational spectrum but the detection of the other phosphate molecular groups is not obvious. The Ga–Al substitution allows better vibrational assignment. MAS-NMR spectra of these two cations show that these two conditional glass former does not behave exactly in the same way in the glassy state.

Vibrational spectrum of KMIIP3O9 tricyclophosphates with the benitoite structure

Abstract The Raman and i.r. spectra of tricyclophosphates KM II P 3 O 9 (M II = Mg, Ca, Co, Mn, Zn, Cd) with the benitoite structure are discussed on the basis of a factor group analysis, and by comparison with the spectrum of the structurally related LaP 3 O 9 . 3 H 2 O. Most of the stretching frequencies have been observed and assigned, whereas the assignment of the bending modes remains more or less hypothetical. Low-frequency i.r. bands have been assigned to translations of either K or M II cations on the basis of mass effects. The influence of the ring chain polymorphism is briefly discussed.

Structural characterization of glassy phases in the system Na2O-Ga2O3-P2O5 by MAS and solution NMR and vibrational spectroscopy: II. Structure of the phosphate network.

The structure of the phosphate network of glasses in the system Na2O-Ga2O3-P2O5 has been investigated as a function of the Na/Ga molar ratio and the phosphate composition corresponding to a mono, di, tri, tetra and meta phosphate stoichiometry. The glass is made of phosphate molecular groups of different lengths linked by the cations with rather ionic (Na) or more covalent (Ga) bonds except in the case of the orthophosphate composition for which we only found isolated PO4(3-) ions. The vibrational spectra are sensitive to composition variations but the band width and the couplings between the different groups prevent any quantitative determination. 31P MAS-NMR gives an in-situ information on the P environment in the glass but the signals are often large and ill defined so that the assignment is not at all straightforward. On the other hand, 31P solution NMR gives sharper signals, allowing more quantitative determinations but the dissolution process always introduces some indeterminacy on the real glass structure which can be minimized by a careful preparation of the solution.

Spectre infra-rouge de quelques oxyhalogénures de bismuth et de terres rares

Abstract The i.r. Spectra of some oxyhalides of Bismuth and of lanthanides exhibit the 4 fundamentals predicted by the group theory. The investigation of oriented thin flaky crystals allows their assignment to either the A2u or the Eu modes. This assignment is the reverse of that recently proposed by B asile et al. The Raman Spectra are often not complete. The relative participation of the different atoms to the various vibrations has been evaluated by an external symmetry coordinate treatment.

Structural characterization of glassy phases in the system Na2O–Ga2O3–P2O5 by MAS-NMR, EXAFS and vibrational spectroscopy. I. Cations coordination

The cationic coordinations of phosphate based gallium sodium glasses in the system Na2O-Ga2O3-P2O5 have been studied by several techniques (71Ga and 23Na MAS-NMR, EXAFS and vibrational spectroscopies) in order to study the relationship between the structure and the chemical composition. We found that three different environments are available for the gallium ions while it is very difficult to get accurate information on the sodium coordinations. Our data show that in orthophosphate glasses, gallium is mainly tetrahedral but when the mean phosphate chain length increases, its coordination becomes more and more octahedral. In these glassy structure, it becomes then possible to dissolve large amounts of typically octahedral cations like Fe3+ or Cr3+.

Infrared spectrum of synthetic isotopic species of sinhalite MgAlBO4

Abstract The i.r. spectra of isotopic species of synthetic sinhalite, MgAlBO 4 , are reported and discussed in relation with a group theoretical analysis. The stretching vibrations of the BO 4 group are observed in the 1150-800 cm −1 region, but no significant 10 B- 11 B isotopic shift is observed in the lower wavenumber region: the identification of the BO 4 bending vibrations is thus impossible; these vibrations are very probably mixed up with lattice vibrations. Several translational modes of the Mg cations have been identified in the 500-300 cm −1 region with the help of 24 Mg- 26 Mg isotopic shifts. The possible assignments for Al translations are also discussed. The large splitting of the ν 3 components of the BO 4 tetrahedron is discussed in connection with the vibrational behavior and the structure of other olivine-type compounds.

Vibrational properties of PbCO3 · PbX2 (X = Cl, Br)

Abstract The i.r. and Raman spectra of PbX 2 · PbCO 3 (X = Cl, Br) have been recorded. The symmetry of the Raman peaks have been assigned on the basis of the data collected on a natural single crystal of phosgenite (X = Cl). The factor group and site group analysis has been discussed in relation to the experimental data.

Vibrational spectrum of AIBIIIO2 and AIBIIIS2 compounds with the rhombohedral α-NaFeO2 structure

Abstract The Raman and i.r. spectra of A I B III X 2 ( X = O or S) compounds with the α-NaFeO 2 rhombohedral structure are reported and discussed on the basis of a group theoretical analysis. Most of the sulfur compounds exhibit the two predicted Raman-active frequencies; they are shown to be independent of the mass of both A I and B III cations and correspond to motions of the anionic lattice. The origin of the 4 i.r. active fundamentals is more complex. The relative influence of A I , B III and X on these frequencies is discussed on the basis of appropriate experimental data.