High-temperature calorimetric study of glass-forming fluorozirconates

I. Ching Lin, Alexandra Navrotsky, John Ballato, Richard E. Riman

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

Abstract

Using high temperature calorimetric techniques, enthalpies of mixing of melts, enthalpies of formation of glasses and enthalpies of formation of crystals have been measured in binary systems ZrF4-BaF2, ZrF4-NaF, ZrF4-LaF3 and selected compositions in the system ZrF4-BaF2-LaF3-AlF3-NaF. The system ZrF4-LaF3 shows essentially zero enthalpies of mixing of melts. In the other systems, there are strongly exothermic enthalpies of mixing. In the binary systems ZrF4-BaF2 and ZrF4-NaF, the enthalpy of mixing of melts and the enthalpy of formation of crystals show minima at the same compositions, Ba2ZrF8 and Na3ZrF7, respectively, indicating the stoichiometric complexes ZrF4-8 and ZrF3-7. These results are discussed in relation to energetics, structure, speciation and acid-base chemistry and suggest the following: ZrF4, LaF3 and AlF3 are anionic complex-formers, while BaF2 and NaF are ionized in the molten state. The coordination number of the zirconium fluoride anionic complex varies with the amount of alkali or alkaline earth fluoride. A model is proposed in which glass-forming melts are dominated by ZrF-5 species and lie near deep eutectics. Therefore, glass formation in fluorozirconates involves a substantial structural change, which is dominated by short-range atomic arrangements, from the melt with predominantly ZrF-5 to the glass where zirconium is 7 or 8 coordinated by fluorine.

Original languageEnglish (US)
Pages (from-to)113-124
Number of pages12
JournalJournal of Non-Crystalline Solids
Volume215
Issue number2-3
DOIs
StatePublished - Jul 1997
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Condensed Matter Physics
  • Materials Chemistry

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