Thermochemistry of rare-earth orthophosphates

S. V. Ushakov, K. B. Helean, A. Navrotsky, L. A. Boatner

Research output: Contribution to journalArticlepeer-review

215 Scopus citations


The enthalpies of formation for the compounds (RE3+)PO4, (where RE = Sc, Y. La-Nd, Sm-Lu) were determined by oxide-melt solution calorimetry. Calorimetric measurements were performed in a Calvet-type twin microcalorimeter in sodium molybdate (3Na2O · 4MoO3) and lead borate (2PbO · 2B2O3) solvents at 975 K. The experiments were carried out using both powdered single crystals grown by a flux technique and powders synthesized by precipitation. Formation enthalpies were derived from the drop-solution enthalpies for (RE)PO4, RE oxides, and P2O5. Enthalpies of formation for the (RE)PO4 compounds with respect to the oxides at 298 K become more negative with increasing RE3+ ionic radius; i.e., in going from ScPO4 (-209.8 ± 1.0 kJ/mol), to LuPO4 (-263.9 ± 1.9 kJ/mol), to LaPO4 (-321.4 ± 1.6 kJ/mol). From structural considerations, a similar trend is expected for the isostructural RE vanadates and arsenates, as well as for the tetravalent actinide orthosilicates.

Original languageEnglish (US)
Pages (from-to)2623-2633
Number of pages11
JournalJournal of Materials Research
Issue number9
StatePublished - Sep 2001
Externally publishedYes

ASJC Scopus subject areas

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


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