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| KCuF3 | |
|---|---|
| Name | Potassium copper(II) fluoride |
| Formula | KCuF3 |
| Molar mass | 157.60 g·mol−1 |
| Appearance | blue-green orthorhombic crystals |
| Density | 2.91 g·cm−3 |
| Melting point | decomposes above 800 °C |
| Solubility | soluble in water, hygroscopic |
KCuF3 is a transition-metal fluoride composed of potassium, copper, and fluorine that has served as a paradigmatic material in studies of low-dimensional magnetism, orbital physics, and electron–lattice coupling. It is notable for exhibiting cooperative Jahn–Teller distortion, quasi-one-dimensional antiferromagnetism, and orbital ordering, making it relevant across experimental programs involving neutron scattering, synchrotron spectroscopy, and theoretical modeling. KCuF3 has been investigated alongside prototypical materials in condensed matter physics and correlated-electron research.
KCuF3 crystallizes in a perovskite-related lattice closely associated with the cubic perovskite archetype first characterized in studies of Perovskite and later compared with materials like CaTiO3, SrTiO3, LaMnO3, YBa2Cu3O7−δ, and K2NiF4. The structure is often described using space groups that reflect cooperative distortions akin to those discussed for Ilmenite and FeO; early single-crystal diffraction work referenced methods from William H. Bragg-era techniques and modernized by instruments at facilities such as Institut Laue–Langevin and synchrotrons like European Synchrotron Radiation Facility. The Cu2+ ions occupy octahedral sites within a fluoride framework, producing corner-sharing CuF6 octahedra that stack to form chains along one crystallographic axis, a motif reminiscent of chain compounds studied in the context of Heisenberg model realizations like KCuO2 and Sr2CuO3.
Chemical bonding in KCuF3 is significantly ionic with appreciable covalency in the Cu–F interaction; this has been compared against bonding pictures used for CuO, Cu2O, NiO, and CoO. Lattice constants and octahedral tilts have been measured in experimental campaigns led by teams associated with Max Planck Society and Brookhaven National Laboratory, and the degree of distortion correlates with theories developed by researchers following the legacy of John B. Goodenough and Junjiro Kanamori.
Electronically, KCuF3 is a Mott–Hubbard-like insulator, a classification often discussed in tandem with V2O3, NiS2, La2CuO4, MnO, and VO2. The Cu2+ (d9) configuration gives rise to a single hole in the eg manifold, leading to strong on-site Coulomb repulsion treated within methods like Hubbard model, Dynamical mean-field theory, Density functional theory, and extensions such as DFT+U and LDA+DMFT. Magnetically KCuF3 exhibits quasi-one-dimensional antiferromagnetism with exchange interactions similar to those in BaCu2Si2O7 and Sr2CuO3; neutron scattering experiments performed at facilities like Oak Ridge National Laboratory and ISIS Neutron and Muon Source have mapped spin-wave dispersions that are compared to predictions from the Bethe ansatz and numerical work influenced by Richard Feynman-style spin chain analyses.
Long-range Néel order occurs at low temperatures, a phenomenon placed in historical context with studies of Louis Néel-type antiferromagnetism and contrasted with low-dimensional spin liquids examined by groups associated with Pauling-era magnetism. Magnetic susceptibility, electron spin resonance, and muon spin rotation experiments have been carried out by collaborations involving CERN-linked instrumentation and regional laboratories such as Argonne National Laboratory.
The cooperative Jahn–Teller distortion in KCuF3, a case study in symmetry breaking described in the foundational works of Hermann Jahn and Edward Teller, produces alternating long and short Cu–F bonds and drives orbital ordering of the eg orbitals. This orbital patterning is analogous to orbital physics discussed for LaMnO3 and K2CuF4 and has been modeled using Kugel–Khomskii-type Hamiltonians developed by K. I. Kugel and D. I. Khomskii. High-resolution X-ray diffraction and resonant X-ray scattering at facilities like SLAC National Accelerator Laboratory and Diamond Light Source have resolved the orbital superstructure; theoretical descriptions draw on work by P. W. Anderson and subsequent computational frameworks such as those advanced by Walter Kohn and Sir Nevill Mott.
The interplay between lattice, spin, and orbital degrees of freedom in KCuF3 provides an experimental realization of concepts central to the Goodenough–Kanamori rules and has influenced research directions pursued by groups at institutions such as MIT, Harvard University, Princeton University, and University of Cambridge.
Typical synthesis routes for KCuF3 employ solid-state reactions starting from reagents like KF and CuF2, echoing preparative techniques used historically for fluorides investigated at laboratories including Bell Labs and university chemistry departments such as those at University of California, Berkeley and University of Oxford. Hydrothermal synthesis and melt-growth methods have been adapted from protocols used for related halides like K2NiF4 and Cs2CuCl4, often under inert atmospheres in gloveboxes supplied by companies mentioned in materials workflows at Argonne National Laboratory. Crystal growth for neutron and X-ray experiments has been performed using Bridgman and flux methods with apparatus referenced in materials studies at Lawrence Berkeley National Laboratory and Forschungszentrum Jülich.
Chemical purity, humidity control, and handling precautions follow standards established by organizations such as American Chemical Society and International Union of Pure and Applied Chemistry for air-sensitive fluorides; analytical characterization typically includes techniques developed at institutions like Stanford University and ETH Zurich.
Optically KCuF3 shows absorption features within the visible and ultraviolet related to d–d transitions and charge-transfer excitations compared to spectra of CuO, CuCl2, and TiO2; spectroscopies using instruments from Rutherford Appleton Laboratory and National Institute of Standards and Technology have been employed. Thermal properties, including specific heat and thermal expansion, have been measured in campaigns analogous to those on La2CuO4 and reported by groups at University of Tokyo and Max Planck Institutes. Electrical transport is insulating with activation energies discussed in contexts similar to Mott insulator materials and characterized using setups pioneered at Bell Labs and IBM Research.
Phonon spectra obtained via Raman and infrared spectroscopy have been used to probe electron–phonon coupling as in studies of MgO and Al2O3; inelastic neutron scattering further elucidates magnon–phonon interactions referenced in work from ISIS and Institut Laue–Langevin.
While KCuF3 is not a commercial commodity like Si or Al2O3, it serves as a benchmark material in basic research into low-dimensional magnetism, orbital physics, and strong correlation phenomena studied at universities and national laboratories such as Columbia University, University of Chicago, Los Alamos National Laboratory, and Cornell University. It has been used in comparative studies that inform understanding of high-temperature superconductors like YBa2Cu3O7−δ and La2−xSrxCuO4, and its role as a model system has influenced theoretical frameworks taught at departments across Princeton University and California Institute of Technology.
Experimental protocols developed for KCuF3 have informed techniques in resonant inelastic X-ray scattering employed at European XFEL and neutron spectroscopy standards at SNS (Spallation Neutron Source). Research on KCuF3 continues to guide inquiries supported by funding agencies such as National Science Foundation and Department of Energy.
Category:Fluorides