Thermochemistry of framework titanosilicate A 2TiSi 6O 15 (A = K, Rb, Cs)

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

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

A new family of framework titanosilicates, A 2TiSi 6O 15 (A = K, Rb, Cs) (space group Cc), has recently been synthesized using the hydrothermal method. This group of phases can potentially be utilized for storage of radioactive elements, particularly 137Cs, due to its high stability under electron radiation and chemical leaching. Here, we report the syntheses and structures of two intermediate members in the series: KRbTiSi 6O 15 and RbCsTiSi 6O 15. Rietveld analysis of powder synchrotron X-ray diffraction data reveals that they adopt the same framework topology as the end-members, with no apparent Rb/K or Rb/Cs ordering. To study energetics of the solid solution series, high-temperature drop-solution calorimetry using molten 2PbO · B 2O 3 as the solvent at 975 K has been performed for the end-members and intermediate phases. As the size of the alkali cation increases, the measured enthalpies of formation from the constituent oxides (ΔH f,ox 0) and from the elements (ΔH f,el 0) become more exothermic, suggesting that this framework structure favors the cation in the sequence Cs +, Rb +, and K +. This trend is consistent with the higher melting temperatures of A 2TiSi 6O 15 phases with increase in the alkali cation size.

Original languageEnglish (US)
Pages (from-to)1819-1825
Number of pages7
JournalJournal of the American Ceramic Society
Volume88
Issue number7
DOIs
StatePublished - Jul 2005
Externally publishedYes

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry

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