TEM study of the electron-doped layered La2-2xCa1+2xMn2O7: Orthorhombic phase in the 0.8<×< 1.0 composition range

Leonid A. Bendersky, Rongji Chen, Ian D. Fawcett, Martha Greenblatt

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21 Scopus citations

Abstract

A series of Ruddlesden-Popper compounds with n = 2 and stoichiometry La2-2XCa1+2xMn2O7 were synthesized by a citrate gel technique and studied by TEM for the composition range 0.8<×<1.0. In sim experiments and analysis of substructure/twins identified structural changes of the I4/mmm phase at low temperatures (200-350°C). Reciprocal space analysis identified superlattice reflections (not previously detected by X ray) and possible space groups. The low-temperature phase belongs to the noncentrosymmetric Cmc21 or Ama2 space group, and the transient Cmcm space group is also possible. These structural transitions do not coincide with the magnetic transitions, which occur below room temperature. A structural model based on tilting of almost-rigid octahedra is suggested for Cmcm and Cmc21. The proposed model for the low-temperature Cmc21 phase has a ΦΦΨz/ΦΦΨz combination of tilts, while the transient Cmcm has a ΦΦ0/ΦΦ0 combination of tilts.

Original languageEnglish (US)
Pages (from-to)309-323
Number of pages15
JournalJournal of Solid State Chemistry
Volume157
Issue number2
DOIs
StatePublished - 2001

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

Keywords

  • Crystallography
  • LaCaMnO
  • Manganates
  • Phase transition
  • TEM

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