Energetics of oxidation of oxynitrides: Zr–N–O, Y–Zr–N–O, Ca–Zr–N–O, and Mg–Zr–N–O

I. Molodetsky, A. Navrotsky, F. DiSalvo, M. Lerch

Research output: Contribution to journalArticlepeer-review

20 Scopus citations

Abstract

The enthalpies of oxidation, ΔHox, of oxynitrides YyZr1-yO2x-0.5y-2/3xNx (0.016 < x < 0.2), CayZr1-yO2x-y-2/3xNx (0.03 < x < 0.14), MgyZr1-yO2x-y-2/3xNx (0.146 < x < 0.28), and Zr–O–N (β-type and γ phases) are measured using drop solution calorimetry in molten sodium molybdate (3Na2O · 4MoO3) at 973 K. Linear relations between the enthalpy ΔHox and nitrogen content were found in all oxynitrides. They indicate that, within the experimental range of nitrogen concentrations, sites occupied by nitrogen ions are energetically equivalent in a given substitutional series. The enthalpies normalized per mole of nitrogen, ΔHnox, for compounds of Y–Zr–N–O, Ca–Zr–N–O, and Zr–N–O are similar, about −500 kJ/(mol of N). A more exothermic value of ΔHnox, of about −950 kJ/(mol of N), is seen in Mg–Zr–N–O compounds. The energetics of vacancy formation in zirconium oxynitrides was determined and compared to the energetics of vacancy formation in yttria- and calcia-stabilized zirconia. The enthalpy of vacancy formation (enthalpy of formation relative to end members normalized per vacancy) in zirconium oxynitrides (−190.5 ± 27.0 kJ/mol of Voö) is more exothermic than that in yttria- and calcia-stabilized zirconia (-105 ± 7.2 and -91.4 ± 3.8 kJ/mol of Voö, respectively). This is consistent with the higher tendency for long-range ordering in zirconium oxynitrides compared to stabilized zirconia. Some technological implications of the results are briefly discussed.

Original languageEnglish (US)
Pages (from-to)2558-2570
Number of pages13
JournalJournal of Materials Research
Volume15
Issue number11
DOIs
StatePublished - Nov 2000
Externally publishedYes

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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