Superprotonic conductivity in Cs3(HSO4)2(H2PO4)

Sossina M. Haile*, Gisela Lentz, Klaus Dieter Kreuer, Joachim Maier

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

93 Scopus citations


Investigations of solid solutions of CsHSO4 and CsH2PO4 have led to the discovery of a new compound with a sulfate to phosphate ratio of 2:1. Single-crystal X-ray data showed the as-synthesized phase to be monoclinic and not isostructural with any known compounds. Ac impedance measurements revealed that, upon heating, the compound undergoes a transformation into a phase of high conductivity at ~ 119 °C. The activation energy dropped from 0.90(2) eV to 0.45(5) eV, while the conductivity jumped from 2.5 × 10-5 Ω-1 cm-1 to 6.3 × 10-3 Ω-1 cm-1. Powder diffraction data suggest that the high-temperature phase is body-centered cubic. Although unlikely, the possibility of a Cs+contribution to the conductivity at elevated temperatures cannot be precluded. Upon cooling, the compound remained in the high conductivity phase until 60-80 °C. At this point it transformed into a third, new phase and the conductivity dropped almost three orders of magnitude, but remained higher than in the as-synthesized compound. Given the similarities between this new compound and CsHSO4, it is likely that high-temperature proton conduction in Cs3(HSO4)2(H2PO4) is facilitated by sulfate and/or phosphate ion reorientations.

Original languageEnglish (US)
Pages (from-to)128-134
Number of pages7
JournalSolid State Ionics
Issue numberC
StatePublished - Jan 1 1995


  • Conductivity-superprotonic
  • Cs(HSO)(HPO)

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics


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