Prototype Sandia octahedral molecular sieve (SOMS) Na2Nb 2O6·H2O: Synthesis, structure and thermodynamic stability

Hongwu Xu, May Nyman, Tina M. Nenoff, Alexandra Navrotsky

Research output: Contribution to journalArticlepeer-review

57 Scopus citations


A new microporous phase Na2Nb2O6· H2O, which transforms to NaNbO3 perovskite on heating, has been synthesized by the hydrothermal method. Rietveld analysis of powder synchrotron X-ray diffraction data reveals that the structure comprises a framework of [NbO6] and [NaO6] octahedra with other Na+ being located in the channels (space group C2/c; a = 17.0511(9) Å; b = 5.0293(2) Å; c = 16.4921(9) Å; β = 113.942(2)°). This phase belongs to the recently synthesized Sandia octahedral molecular sieves (SOMS) family, Na2Nb2-xM xO6-x-(OH)x·H2O (M = Ti, Zr) and is the archetype for the substituted structures. Using drop-solution calorimetry into molten 3Na2O·4MoO3 at 974 K, the enthalpies of formation of Na2-Nb2O6· H2O from the constituent oxides and from the elements have been determined to be -295.4 ± 4.8 and -2895.5 ± 6.4 kJ/mol, respectively. From the drop-solution calorimetric data for Na2Nb 2O6·H2O and its dehydrated perovskite phase, the enthalpy of the dehydration reaction, Na2Nb 2O6·H2O → 2NaNbO3 + H2O, has been derived, and its implications for phase stability are discussed.

Original languageEnglish (US)
Pages (from-to)2034-2040
Number of pages7
JournalChemistry of Materials
Issue number10
StatePublished - May 18 2004
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry


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