title: Perovskite to postperovskite transition in NaFeF3.
abstract: The GdFeO3-type perovskite NaFeF3 transforms to CaIrO3-type postperovskite at pressures as low as 9 GPa at room temperature. The details of such a transition were investigated by in situ synchrotron powder diffraction in a multianvil press. Fit of the p-V data showed that the perovskite phase is more compressible than related chemistries with a strongly anisotropic response of the lattice metrics to increasing pressure. The reduction in volume is accommodated by a rapid increase of the octahedral tilting angle, which reaches a critical value of 26° at the transition boundary. The postperovskite form, which is fully recoverable at ambient conditions, shows a regular geometry of the edge-sharing octahedra and its structural properties are comparable to those found in CaIrO3-type MgSiO3 at high pressure and temperature. Theoretical studies using density functional theory at the GGA + U level were also performed and describe a scenario where both perovskite and postperovskite phases can be considered Mott-Hubbard insulators with collinear magnetic G- and C-type antiferromagnetic structures, respectively. Magnetic measurements are in line with the theoretical predictions with both forms showing the typical behavior of canted antiferromagnets.
authors.affiliation: Chemistry Department and Centre for Material Science and Nanotechnology and §Department of Physics, University of Oslo , NO-0315 Oslo, Norway.
authors.forename: Fabian L
authors.initials: FL
authors.lastname: Bernal
authors.forename: Kirill V
authors.initials: KV
authors.lastname: Yusenko
authors.forename: Jonas
authors.initials: J
authors.lastname: Sottmann
authors.forename: Christina
authors.initials: C
authors.lastname: Drathen
authors.forename: Jérémy
authors.initials: J
authors.lastname: Guignard
authors.forename: Ole Martin
authors.initials: OM
authors.lastname: Løvvik
authors.forename: Wilson A
authors.initials: WA
authors.lastname: Crichton
authors.forename: Serena
authors.initials: S
authors.lastname: Margadonna