Structural variation in Ca(TixSi1-x)O3 perovskites (1>x>0.65) and the ordered phase Ca2TiSiO6

Kurt Leinenweber, A. Grzechnik, M. Voorhees, A. Navrotsky, A. Yao, F. F. McMillan

Research output: Contribution to journalArticle

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Abstract

High pressure perovskites in the system CaTiO3-CaSiO3 in the composition range from 0 to 50% CaSiO3 have been re-examined using powder x-ray diffraction, Raman spectroscopy, and transmission electron microscopy. In runs performed at 9 GPa and 1200 °C, a solid solution is obtained with compositions ranging from CaTiO3 to near Ca(Ti0.65Si.,0.35)O3, and with the orthorhombic distortion in the CaTiO3 end-member diminishing to pseudocubic for Ca(Ti0.65Si0.35)O3. Raman spectra show intensity changes and band broadening which are attributed to the reduction of orthorhombic character, but still indicate lower than cubic symmetry for the entire solid solution range. An ordered intermediate, Ca2TiSiO6, has been recovered from a run at 14 GPa at 1200 °C. The space group is Fm3m, with a=7.410(2) Å, and the compound has the double perovskite structure. In this structure, Si-rich octahedral sites and Ti-rich octahedral sites alternate along the three principal axes. Transmission electron microscopy confirms the presence of the Fm 3m ordered structure, and also documents the presence of lesser amounts of at least three other ordered perovskite structures which are not resolved in the x-ray data. These may account for extra features observed in the Raman spectrum which are inconsistent with mode assignments for the Fm3m phase. Non face-centered ordering schemes for these regions are suggested based on modeling of the HRTEM patterns.

Original languageEnglish (US)
Pages (from-to)528-534
Number of pages7
JournalPhysics and Chemistry of Minerals
Volume24
Issue number7
DOIs
StatePublished - Jan 1 1997

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perovskite
solid solution
Perovskite
Raman scattering
transmission electron microscopy
Solid solutions
Transmission electron microscopy
X rays
Raman spectroscopy
Chemical analysis
diffraction
symmetry
Diffraction
Powders
modeling
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ASJC Scopus subject areas

  • Materials Science(all)
  • Geochemistry and Petrology

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Structural variation in Ca(TixSi1-x)O3 perovskites (1>x>0.65) and the ordered phase Ca2TiSiO6 . / Leinenweber, Kurt; Grzechnik, A.; Voorhees, M.; Navrotsky, A.; Yao, A.; McMillan, F. F.

In: Physics and Chemistry of Minerals, Vol. 24, No. 7, 01.01.1997, p. 528-534.

Research output: Contribution to journalArticle

Leinenweber, Kurt ; Grzechnik, A. ; Voorhees, M. ; Navrotsky, A. ; Yao, A. ; McMillan, F. F. / Structural variation in Ca(TixSi1-x)O3 perovskites (1>x>0.65) and the ordered phase Ca2TiSiO6 In: Physics and Chemistry of Minerals. 1997 ; Vol. 24, No. 7. pp. 528-534.
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abstract = "High pressure perovskites in the system CaTiO3-CaSiO3 in the composition range from 0 to 50{\%} CaSiO3 have been re-examined using powder x-ray diffraction, Raman spectroscopy, and transmission electron microscopy. In runs performed at 9 GPa and 1200 °C, a solid solution is obtained with compositions ranging from CaTiO3 to near Ca(Ti0.65Si.,0.35)O3, and with the orthorhombic distortion in the CaTiO3 end-member diminishing to pseudocubic for Ca(Ti0.65Si0.35)O3. Raman spectra show intensity changes and band broadening which are attributed to the reduction of orthorhombic character, but still indicate lower than cubic symmetry for the entire solid solution range. An ordered intermediate, Ca2TiSiO6, has been recovered from a run at 14 GPa at 1200 °C. The space group is Fm3m, with a=7.410(2) {\AA}, and the compound has the double perovskite structure. In this structure, Si-rich octahedral sites and Ti-rich octahedral sites alternate along the three principal axes. Transmission electron microscopy confirms the presence of the Fm 3m ordered structure, and also documents the presence of lesser amounts of at least three other ordered perovskite structures which are not resolved in the x-ray data. These may account for extra features observed in the Raman spectrum which are inconsistent with mode assignments for the Fm3m phase. Non face-centered ordering schemes for these regions are suggested based on modeling of the HRTEM patterns.",
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