Marie-Hélène Chopinet

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.

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.