Annie Blin

Infrared reflectivity spectroscopy of silicate glasses

Infrared reflection spectra of more than fifty silicate glasses have been obtained with a Fourier-transform infrared spectrometer and are reported in the range from 20 to 4000 cm −1 . Results have been systematically analysed with both Kramers-Kronig inversion and fit of the factorized form of the dielectric function to reflectivity spectra. Good agreement between both methods has been found. The detailed analysis of this set of data shows localized modes characteristic of the response of cations like Na, K or Ca, as opposed to the coupled-mode behavior of Al-O-Si vibrations. The degree of coherence of vibrations is also discussed. The specific potentialities of this spectroscopy and the kind of conclusions that can be drawn about the structure of silica glasses — when complete spectra are available — is illustrated by several examples in silica glasses containing Na, K, Ca, Al, Zr, F, B or Mg ions.

A multispectroscopic study of PbOxZnO0.6−x(P2O5)0.4 glasses

Abstract The structure of ternary PbO x –ZnO (0.6− x ) –(P 2 O 5 ) 0.4 glasses has been investigated using nuclear magnetic resonance (NMR), Raman scattering and infrared spectroscopy (IR), over the compositional range from x =0 to 0.6. The evolution of the 31 P NMR chemical shift and Raman high-frequency modes reflects mainly the Zn/Pb substitution in these glasses. The NMR and Raman spectra show that at high ZnO content, the phosphate network has a strong interaction with Zn cations through P–O–Zn bonds. In glasses with high lead content, IR reflectivity spectra indicate that the phosphate network and lead cation are less correlated and that Pb 2+ has a mixed network former–network modifier role in the glass structure.

Comparison of dielectric response deduced from infrared reflectivity and Raman spectra of silicate glasses

Abstract The infrared response of twenty silicate glasses deduced both from a Kramers-Kronig analysis and from a fit of dielectric function model to simulate infrared reflectivity spectra in the wavenumber range 20–4000 cm −1 is compared with Raman spectra of the same samples in polarized light. Galeenar and Lucovsky first noted that peaks corresponding to transverse and lingitudinal optic modes deduced from the analysis of infrared reflectivity spectra appear in the Raman spectra of vitreous SiO 2 and GeO 2 . In the present paper this result is confirmed for SiO 2 , but no similar correspondence of infrared and Raman mode is observed in any of the silicate glasses investigated. Infrared and Raman responses in fact appear more and more different as the percentage of SiO 2 in the glass is reduced. Effective ionic charges of oxygen are deduced from infrared data and found to increase significantly with the decrease of the fraction of glass former constituents.

Fano effect in glasses

Abstract An interference between the discrete states of coherent vibrations of the silica network and the broad continuum of incoherent motions of Na cations has been observed in glasses containing sodium. The effect is very marked when the Na composition exceeds 45% of the cations. The spectra of silicate glasses composed of heavy cations like lead or lanthanum contrast with those of sodium glasses. They do not show Fano-type interference lineshapes and are fitted with Lorentzian profiles satisfactorily.

Synthesis and electrical properties of Ba(Sn0.7Sb0.3)O3

Abstract BaSn 0.7 Sb 0 . 3 O 3 has been synthesized for the first time. This result is original because up to now the solubility limit of the Ba(Sn 1− x Sb x )O 3 series was found to be x =0.2. The electronic carrier concentration is prevented from screening phonons via infrared reflectivity spectra. Whereas a transition from metal to superconductor behaviour is observed upon substituting Pb for Bi in the perovskite Ba(Pb,Bi)O 3 system, no similar transition was observed in the Ba(Sn,Sb)O 3 system, although these systems have the same structure. The phenomen of 3+/5+ disproportionation exists in both systems. The octahedra are occupied by cations exhibiting the same valence. The electronic carrier concentration is similar but superconductivity is not observed in the Ba(Sn,Sb)O 3 system. The correlation between metallicity and structure is studied.

Infrared reflectivity spectroscopy of nitrogen-substituted alkaline earth aluminosilicate glasses

Abstract Infrared reflectivity spectra of the series M 0.37 Si 0.53 Al 0.10 O 1.58−3χ/2 N χ with M  Mg, Ca and Ba and χ varying between 0 and 0.09 are reported. The far-infrared vibrational frequency of the M cation mainly depends on cationic mass. In the case of magnesium, the vibrational frequency is also sensitive to the coordination implying the glass-former (tetrahedral) or glass-modifier (likely octahedral). The anionic effective charge measured from the Coulombic contribution to the infrared reflection bands is smaller in nitrogenated glasses than in oxide glasses, showing an increased average bond hybrization, consistent with hardening of the structure indicated by macroscopic properties.