Silicon nitride: enthalpy of formation of the α- and β-polymorphs and the effect of C and O impurities

Jian Jie Liang, Letitia Topor, Alexandra Navrotsky, Mamoru Mitomo

Research output: Contribution to journalArticlepeer-review

52 Scopus citations

Abstract

High-temperature oxidative drop solution calorimetry was used to measure the enthalpy of formation of α- and β-Si3N4. Two different solvents, molten alkali borate (48 wt% LiBO2 · 52 wt% NaBO2) at 1043 and 1073 K and potassium vanadate (K2O · 3V2O5) at 973 K, were used, giving the same results. Pure α- and β-Si3N4 polymorphs have the same molar enthalpy of formation at 298 K of -850.9 ± 22.4 and -852.0 ± 8.7 kJ/mol, respectively. The unit cell dimensions of impure α-Si3N4 samples depend linearly on the O and C impurity contents, and so does the molar enthalpy of formation. The energetic stability of the α-Si3N4 phase decreases when the sample contains O and C impurities. The experimental evidence strongly suggests that the impurities dissolve into the α-Si3N4 structure to form a (limited) isostructural solid solution series but that this solid solution series is energetically less stable than a mechanical mixture of pure (α or β) Si3N4, SiO2, and SiC. Thus, the α-phase is not stabilized by impurities and is probably always metastable.

Original languageEnglish (US)
Pages (from-to)1959-1968
Number of pages10
JournalJournal of Materials Research
Volume14
Issue number5
DOIs
StatePublished - May 1999
Externally publishedYes

ASJC Scopus subject areas

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

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