Geometric frustration of Jahn–Teller order in the infinite-layer lattice
- SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Stanford Univ., CA (United States)
- Cornell Univ., Ithaca, NY (United States)
- SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Univ. of Florida, Gainesville, FL (United States)
- Pohang Univ. of Science and Technology (POSTECH) (Korea, Republic of)
- SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)
The Jahn–Teller effect, in which electronic configurations with energetically degenerate orbitals induce lattice distortions to lift this degeneracy, has a key role in many symmetry-lowering crystal deformations. Lattices of Jahn–Teller ions can induce a cooperative distortion, as exemplified by LaMnO3. Although many examples occur in octahedrally or tetrahedrally coordinated transition metal oxides due to their high orbital degeneracy, this effect has yet to be manifested for square-planar anion coordination, as found in infinite-layer copper, nickel, iron and manganese oxides. Here, for this work, we synthesize single-crystal CaCoO2 thin films by topotactic reduction of the brownmillerite CaCoO2.5 phase. We observe a markedly distorted infinite-layer structure, with ångström-scale displacements of the cations from their high-symmetry positions. This can be understood to originate from the Jahn–Teller degeneracy of the dxz and dyz orbitals in the d7 electronic configuration along with substantial ligand–transition metal mixing. A complex pattern of distortions arises in a $$2\sqrt2$$ x $$2\sqrt2$$ x $$1$$ tetragonal supercell, reflecting the competition between an ordered Jahn–Teller effect on the CoO2 sublattice and the geometric frustration of the associated displacements of the Ca sublattice, which are strongly coupled in the absence of apical oxygen. As a result of this competition, the CaCoO2 structure forms an extended two-in–two-out type of Co distortion following ‘ice rules’.
- Research Organization:
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
- Sponsoring Organization:
- Gordon and Betty Moore Foundation; National Science Foundation (NSF); US Air Force Office of Scientific Research (AFOSR); USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)
- Grant/Contract Number:
- AC02-76SF00515; AC05-00OR22725
- OSTI ID:
- 1996651
- Alternate ID(s):
- OSTI ID: 1975261
- Journal Information:
- Nature (London), Journal Name: Nature (London) Journal Issue: 7951 Vol. 615; ISSN 0028-0836
- Publisher:
- Nature Publishing GroupCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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