Energetics of cobalt phosphate frameworks: α, β, and red NaCoPO4

So Nhu Le, Hank W. Eng, Alexandra Navrotsky

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

Thermal behavior, relative stability, and enthalpy of formation of α (pink phase), β (blue phase), and red NaCoPO4 are studied by differential scanning calorimetry, X-ray diffraction, and high-temperature oxide melt drop solution calorimetry. Red NaCoPO4 with cobalt in trigonal bipyramidal coordination is metastable, irreversibly changing to α NaCoPO4 at 827 K with an enthalpy of phase transition of -17.4±6.9 kJ mol-1. α NaCoPO4 with cobalt in octahedral coordination is the most stable phase at room temperature. It undergoes a reversible phase transition to the β phase (cobalt in tetrahedra) at 1006 K with an enthalpy of phase transition of 17.6±1.3 kJ mol-1. Enthalpy of formation from oxides of α, β, and red NaCoPO4 are -349.7±2.3, -332.1±2.5, and -332.3±7.2 kJ mol-1; standard enthalpy of formation of α, β, and red NaCoPO4 are -1547.5±2.7, -1529.9±2.8, and -1530.0±7.3 kJ mol-1, respectively. The more exothermic enthalpy of formation from oxides of β NaCoPO4 compared to a structurally related aluminosilicate, NaAlSiO4 nepheline, results from the stronger acid-base interaction of oxides in β NaCoPO4 (Na2O, CoO, P2O5) than in NaAlSiO4 nepheline (Na2O, Al2O3, SiO2).

Original languageEnglish (US)
Pages (from-to)3731-3738
Number of pages8
JournalJournal of Solid State Chemistry
Volume179
Issue number12
DOIs
StatePublished - Dec 2006
Externally publishedYes

Keywords

  • Cobalt phosphate framework
  • Enthalpy of formation
  • NaCoPO
  • Phase transformation

ASJC Scopus subject areas

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

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