Phase transition in CaGeO3 perovskite: Evidence from X-ray powder diffraction, thermal expansion and heat capacity

X. Liu, Y. Wang, R. C. Liebermann, P. D. Maniar, A. Navrotsky

Research output: Contribution to journalArticlepeer-review

35 Scopus citations

Abstract

High-temperature x-ray powder diffraction study by the full pattern Rietveld method of orthorhombic CaGeO3 (Pbnm at ambient condition) perovskite confirms the previously observed phase transition at T c=520 K. The measured volumetric thermal expansion coefficients are 3.1 x 10-5 (K-1) below Tc and 3.5x 10-5 (K-1) above Tc. The space group at T>Tc has been tentatively identified as Cmcm. Such a transition involves the disappearance of one of the two octahedral rotations in the (001) plane, and the doubling of the unit cell volume, with c axis unchanged. Although this transition should be of first order from symmetry considerations, the distortion of the Pbnm phase decreases continuously as the temperate approaches Tc and there is no observable volume discontinuity at Tc. The measured heat capacity places an upper limit on the enthalpy of transition of 50 J/mol, which is quite reasonable in terms of the crystallographic nature of this phase transition.

Original languageEnglish (US)
Pages (from-to)224-230
Number of pages7
JournalPhysics and Chemistry of Minerals
Volume18
Issue number4
DOIs
StatePublished - Dec 1991
Externally publishedYes

ASJC Scopus subject areas

  • Materials Science(all)
  • Geochemistry and Petrology

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