High-temperature phase transitions in K3H(SO4)2

Calum R I Chisholm, Sossina M. Haile*

*Corresponding author for this work

Research output: Contribution to journalConference articlepeer-review

36 Scopus citations


Two phase transitions in K3H(SO4)2 were discovered in the temperature range 25-300°C. The transition temperatures for the mid and high-temperature phases are Tc = 190°C (ΔH = 17.0 kJ/mol) and Tc = 227°C (ΔH = 7.4 kJ/mol), respectively, for freshly heated samples. A slow decomposition process begins above 270°C. The conductivity of K3H(SO4)2 in these phases (σ = 1.68 × 10-3 at 198°C and 2.19 × 10-2 Ω-1 cm-1 at 251°C) is comparable to that of other M3H(XO4)2 compounds (M = Cs, NH4, Rb and X = S, Se) in their superprotonic phases. The activation energy for proton transport in the highest temperature phase of K3H(SO4)2 is 0.45 eV, a value slightly higher than in the related compounds. Despite the similarity between the electrical properties of K3H(SO4)2 and other M3H(XO4)2 compounds, the structural properties are quite distinct. Specifically, high-temperature X-ray powder diffraction measurements show that neither of the high-temperature phases of K3H(SO4)2 is trigonal, indeed, the symmetry of the structure decreases at the first transition, in contrast to the superprotonic phases in other M3H(XO4)2 compounds.

Original languageEnglish (US)
Pages (from-to)179-184
Number of pages6
JournalSolid State Ionics
Issue number1-4
StatePublished - Dec 1 2001
Event10th International Conference on Solid State (SSPC10) - Montpellier, France
Duration: Sep 24 2000Sep 28 2000


  • KH(SO)
  • RbH(SeO)
  • Superprotonic phase transitions

ASJC Scopus subject areas

  • General Chemistry
  • General Materials Science
  • Condensed Matter Physics


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