Calorimetric and single crystal X-ray study of the phase transition of (PyH)2PdCl4

T. Asaji, H. Fujimori, Hiroyuki Ishida, K. Eda, M. Hashimoto, M. Oguni

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Abstract

Polymorphic transition of pyridinium tetrachloropalladate(II) was investigated by heat capacity measurements and by single crystal X-ray structural analysis. A large λ-type anomaly was detected at 240 K in the temperature dependence of the heat capacity. The low-temperature phase (LTP) belongs to the triclinic space group P1̄ with a=6.856(1), b=7.293(1), c=7.721(1) Å, α=75.180(2)°, β=71.081(2)°, γ=81.109(3)° at 100 K, and the high-temperature phase (HTP) to the same space group P1̄ with a=7.217(2), b=7.470(2), c=7.880(2) Å, α=73.438(3)°, β=65.195(3)°, γ=82.727(4)° at 293 K. The pyridinium cations are ordered antiferroelectrically in LTP. In HTP, however, an orientational disorder of the cation was observed. The energy difference between potential wells for the reorientation of pyridinium ion in HTP is discussed referring to the results of the present single crystal X-ray and heat capacity as well as the previous 1H NMR measurements. A five-site disorder model is shown to be consistent with both of the observations of 1H NMR and X-ray study.

Original languageEnglish
Pages (from-to)869-875
Number of pages7
JournalJournal of Physics and Chemistry of Solids
Volume66
Issue number5
DOIs
Publication statusPublished - May 2005

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Keywords

  • C. X-ray diffraction
  • D. Crystal structure
  • D. Nuclear quadrupole resonance (NQR)
  • D. Phase transition
  • D. Specific heat

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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