TY - JOUR
T1 - CaFeO2
T2 - A new type of layered structure with iron in a distorted square planar coordination
AU - Tassel, Cédric
AU - Pruneda, José Miguel
AU - Hayashi, Naoaki
AU - Watanabe, Takashi
AU - Kitada, Atsushi
AU - Tsujimoto, Yoshihiro
AU - Kageyama, Hiroshi
AU - Yoshimura, Kazuyoshi
AU - Takano, Mikio
AU - Nishi, Masakazu
AU - Ohoyama, Kenji
AU - Mizumaki, Masaichiro
AU - Kawamura, Naomi
AU - Fniguez, Jorge
AU - Canadell, Enric
PY - 2009/1/14
Y1 - 2009/1/14
N2 - CaFeO2, a material exhibiting an unprecedented layered structure containing 3d6 iron in a high-spin distorted square-planar coordination, is reported. The new phase, obtained through a low-temperature reduction procedure using calcium hydride, has been characterized through powder neutron diffraction, synchrotron X-ray diffraction, Mössbauer spectroscopy, XAS experiments as well as first-principles DFT calculations. The XAS spectra near the Fe-K edge for the whole solid solution (Sr 1-xCax)FeO2 supports that iron is in a square-planar coordination for 0 ≤ x ≤ 0.8 but clearly suggests a change of coordination for x = 1. The new structure contains infinite FeO2 layers in which the FeO4 units unprecedentedly distort from square-planar toward tetrahedra and rotate along the c-axis, in marked contrast to the well-studied and accepted concept that octahedral rotation in perovskite oxides occurs but the octahedral shape is kept almost regular. The new phase exhibits high-spin configuration and G-type antiferromagnetic ordering as in SrFeO2. However, the distortion of the FeO2 layers leads to only a slight decrease of the Néel temperature with respect to SrFeOx. First-principles DFT calculations provide a clear rationalization of the structural and physical observations for CaFeO 2 and highlight how the nature of the cation influences the structural details of the AFeO2 family of compounds (A = Ca, Sr, Ba). On the basis of these calculations the driving force for the distortion of the FeO2 layers in CaFeO2 is discussed.
AB - CaFeO2, a material exhibiting an unprecedented layered structure containing 3d6 iron in a high-spin distorted square-planar coordination, is reported. The new phase, obtained through a low-temperature reduction procedure using calcium hydride, has been characterized through powder neutron diffraction, synchrotron X-ray diffraction, Mössbauer spectroscopy, XAS experiments as well as first-principles DFT calculations. The XAS spectra near the Fe-K edge for the whole solid solution (Sr 1-xCax)FeO2 supports that iron is in a square-planar coordination for 0 ≤ x ≤ 0.8 but clearly suggests a change of coordination for x = 1. The new structure contains infinite FeO2 layers in which the FeO4 units unprecedentedly distort from square-planar toward tetrahedra and rotate along the c-axis, in marked contrast to the well-studied and accepted concept that octahedral rotation in perovskite oxides occurs but the octahedral shape is kept almost regular. The new phase exhibits high-spin configuration and G-type antiferromagnetic ordering as in SrFeO2. However, the distortion of the FeO2 layers leads to only a slight decrease of the Néel temperature with respect to SrFeOx. First-principles DFT calculations provide a clear rationalization of the structural and physical observations for CaFeO 2 and highlight how the nature of the cation influences the structural details of the AFeO2 family of compounds (A = Ca, Sr, Ba). On the basis of these calculations the driving force for the distortion of the FeO2 layers in CaFeO2 is discussed.
UR - http://www.scopus.com/inward/record.url?scp=62649153473&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=62649153473&partnerID=8YFLogxK
U2 - 10.1021/ja8072269
DO - 10.1021/ja8072269
M3 - Article
C2 - 19128179
AN - SCOPUS:62649153473
VL - 131
SP - 221
EP - 229
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 1
ER -