SHORT RANGE STRUCTURES OF FLUORIDE GLASSES

Résumé
La structure à courte distance des verres de fluorozirconate et de fluorohafnate a été étudiée par spectroscopie vibrationelle, diffraction des neutrons et des rayons X, et spectroscopie de photoémission X. Les deux premières méthodes suggèrent que l'environnement en fluor des atomes Zr et Hf possède une symétrie élevée, avec des coordinations essentiellement 6 et 7. Le calcul donne un nombre de coordination F-F voisin de 5. La photoémission X donne des informations moins directes et ne permet pas de distinguer clairement les fluor pontants des non-pontants. Les proportions relatives de ces deux types d'atomes ont cependant une influence observable sur la structure de la bande de valence des fluorozirconates vitreux et cristallins.

Abstract
The short range structures of fluorozirconate and fluorohafnate glasses have been examined by vibrational spectroscopy, X-ray and neutron diffraction and X-ray photoemission spectroscopy. Results from the first two techniques were consistent with the occurrence of highly symmetrical fluorine atom environments about Zr and Hf atoms, with predominant coordinations between 6 and 7-fold. The F-F coordination number was calculated at -5. X-ray photoemission spectroscopy offered somewhat more indirect information, being unable at present to offer a clear distinction between bridging and non-bridging fluorine atoms. The degree of bridging, however, had a significant effect on the structure observed in the valence band of both vitreous and crystalline fluorozirconates.