Structure, Magnetism, and Properties of Ruddlesden-Popper Calcium Manganates Prepared from Citrate Gels

Ian D. Fawcett, Joseph E. Sunstrom IV, Martha Greenblatt, Mark Croft, K. V. Ramanujachary

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Ruddlesden-Popper (RP) phases with the formula (CaO)(CaMnO3)n, where n = 1, 2, 3, and ∞, have been prepared using the Pechini citrate gel process at temperatures as low as 900°C under flowing oxygen. The compounds were characterized by X-ray powder diffraction, Rietveld profile analysis, thermal gravimetric analysis, iodometric titrations, Mn K-edge X-ray absorption spectroscopy, temperature-dependent magnetic susceptibility, and resistivity. Rietveld analysis shows that there is an elongation in the apical Mn-O distances of the MnO6 octahedra, which increases with decreasing dimensionality. Mn K-edge X-ray absorption spectroscopy and iodometric titrations show no detectable amount of Mn3+ (a Jahn-Teller distorted d4 ion) in the samples indicating that the MnO6 deformation may be associated with a splitting in the half-filled t2g levels of Mn4+. Magnetic susceptibility measurements show spontaneous magnetic ordering to antiferromagnetic states at ∼125 K for CaMnO3 and Ca4Mn3O10 and at ∼110 K for Ca2MnO4 and Ca3Mn2O7. The effective magnetic moment is greatly suppressed in all of the RP manganates, even in the three-dimensional CaMnO3, n = ∞ phase, and decreases dramatically with decreasing dimensionality. Large deviations from Curie-Weiss behavior are observed above the ordering temperature, which increase with decreasing n. These observations are discussed in terms of two-dimensional magnetic fluctuations and alternative mechanisms. The compounds are all poor electronic conductors with room-temperature resistivities in the range of 102-104 Ω cm.

Original languageEnglish (US)
Pages (from-to)3643-3651
Number of pages9
JournalChemistry of Materials
Issue number11
StatePublished - Nov 1998

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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