Phase transition of potassium sulfate, K2SO4 (III); thermodynamical and phenomenological study

Michihiro Miyake, Shin ichi Iwai

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)

Abstract

The orthorhombic-hexagonal phase transition of K2SO4 has been investigated by measurements of the temperature dependencies of the specific heat, expansion, and X-ray intensity of superstructure reflections, correlated with the structural point of view. The values of the net enthalpy and entropy changes are ΔH=4.28 KJ/mol and ΔS=4.98 J/mol·K at the phase transition temperature (587°C), respectively. The thermal expansion along the c axis shows strong anisotropic character above about 300°C and exhibits a very large discontinuous increase at 587°C, whereas those along the a and b axes increase linearly and exhibit small discontinuous decreases at 587°C. The X-ray intensity of superstructure reflections in the low-temperature form gradually decrease with increasing temperature, and come to extinction at 587°C, exhibiting a discontinuity. The observed entropy change and pressure dependence of the phase transition temperature were explained successfully by the use of results of the structural analysis and measured physical properties. The temperature dependencies of the spontaneous strain, X-ray intensity of superstructure reflection, and birefringence were consistently described by introducing a transition parameter on the basis of an instability at the M point in the Brillouin zone of the hexagonal phase.

Original languageEnglish
Pages (from-to)211-215
Number of pages5
JournalPhysics and Chemistry of Minerals
Volume7
Issue number5
DOIs
Publication statusPublished - Nov 1981
Externally publishedYes

ASJC Scopus subject areas

  • Materials Science(all)
  • Geochemistry and Petrology

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