Impact of lanthanoid substitution on the structural and physical properties of an infinite-layer iron oxide

The effect of lanthanoid (Ln = Nd, Sm, Ho) substitution on the structural and physical properties of the infinite-layer iron oxide SrFeO2 was investigated by X-ray diffraction (XRD) at ambient and high pressure, neutron diffraction, and 57Fe Mössbauer spectroscopy. Ln for Sr substituted samples up to ∼30% were synthesized by topochemical reduction using CaH2. While the introduction of the smaller Ln3+ ion reduces the a axis as expected, we found an unusual expansion of the c axis as well as the volume. Rietveld refinements along with pair distribution function analysis revealed the incorporation of oxygen atoms between FeO2 layers with a charge-compensated composition of (Sr1–xLnx)FeO2+x/2, which accounts for the failed electron doping to the FeO2 layer. The incorporated partial apical oxygen or the pyramidal coordination induces incoherent buckling of the FeO2 sheet, leading to a significant reduction of the Néel temperature. High-pressure XRD experiments for (Sr0.75Ho0.25)FeO2.125 suggest a possible stabilization of an intermediate spin state in comparison with SrFeO2, revealing a certain contribution of the in-plane Fe–O distance to the pressure-induced transition. © 2016 American Chemical Society

Keywords

X-ray diffraction, Neutron diffraction, Iron, Redox reactions, Crystal lattices, Oxygen

Citation

Yamamoto, T., Ohkubo, H., Tassel, C., Hayashi, N., Kawasaki, S., Okada, T., Yagi, T., Hester, J., Avdeev, M., Kobayashi, Y., & Kageyama, H. (2016). Impact of lanthanoid substitution on the structural and physical properties of an infinite-layer iron oxide. Inorganic Chemistry, 55(22), 12093-12099. doi:10.1021/acs.inorgchem.6b02513