title: Local and Cooperative Jahn-Teller Effect and Resultant Magnetic Properties of M2AgF4(M = Na-Cs) Phases.
abstract: The crystal structure, magnetic properties, heat capacity, and Raman spectra of double-perovskite M2AgF4(M = K, K3/4Rb1/4, K1/2Rb1/2, K1/4Rb3/4, and Rb) phases have been examined, adding to the body of previous results for the M = Na, Cs derivatives. The results suggest that double-perovskite K2AgF4adopts a disordered orthorhombic Bmab structure with an antiferrodistortive arrangement of the elongated and tilted [AgF6] octahedra rather than the structure with the ferrodistortive arrangement of compressed octahedra, as suggested previously (Mazej, Z.; Goreshnik, E.; Jagličić, Z.; Gaweł, B.; Łasocha, W.; Grzybowska, D.; Jaroń, T.; Kurzydłowski, D.; Malinowski, P. J.; Koźmiński, W.; Szydłowska, J.; Leszczyński, P. J.; Grochala, W. KAgF3, K2AgF4and K3Ag2F7: important steps towards a layered antiferromagnetic fluoroargentate(II). CrystEngComm 2009, 11, 1702-1710). A re-examination of the previously collected single-crystal X-ray diffraction data confirms the current structure assignment, and it is also in agreement with recent theoretical calculations. High-field electron paramagnetic resonance spectra reaffirm the presence of elongated [AgF6] octahedra in the crystal structure of all M2AgF4phases studied. The local structure of the M = K derivative is most complex, with regions of the sample that are quite orthorhombically distorted, whereas other regions more closely resemble the tetragonal phase. The mixed-cation K/Rb phases are also inhomogeneous, containing regions of the pure K compound and regions of another high-symmetry phase (likely tetragonal) of a mixed (Rb-richer) compound with unknown composition. The temperature-resolved phase diagram of all K/Rb phases has been established and positioned within the entire M = Na, K, Rb, Cs series.
authors.affiliation: Centre of New Technologies, University of Warsaw , Banacha 2c, 02-097, Warsaw, Poland.|Faculty of Mathematics and Natural Sciences, Cardinal Stefan Wyszynski University in Warsaw , Wóycickiego 1/3, 01-938, Warsaw, Poland.
authors.forename: Dominik
authors.initials: D
authors.lastname: Kurzydłowski
authors.affiliation: Centre of New Technologies, University of Warsaw , Banacha 2c, 02-097, Warsaw, Poland.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Jaroń
authors.affiliation: National High Magnetic Field Laboratory, Florida State University , 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310, United States.
authors.forename: Andrew
authors.initials: A
authors.lastname: Ozarowski
authors.affiliation: National High Magnetic Field Laboratory, Florida State University , 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310, United States.|Department of Physics, Florida State University , Tallahassee, Florida 32306, United States.
authors.forename: Stephen
authors.initials: S
authors.lastname: Hill
authors.affiliation: Faculty of Civil and Geodetic Engineering, Institute of Mathematics, Physics and Mechanics, University of Ljubljana , Jadranska 19, SI-1000, Ljubljana, Slovenia.
authors.forename: Zvonko
authors.initials: Z
authors.lastname: Jagličić
authors.affiliation: Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain , Place L. Pasteur, B-1348, Louvain-la-Neuve, Belgium.
authors.forename: Yaroslav
authors.initials: Y
authors.lastname: Filinchuk
authors.affiliation: Department of Inorganic Chemistry and Technology, Jožef Stefan Institute , Jamova 39, SI-1000, Ljubljana, Slovenia.
authors.forename: Zoran
authors.initials: Z
authors.lastname: Mazej
authors.affiliation: Centre of New Technologies, University of Warsaw , Banacha 2c, 02-097, Warsaw, Poland.
authors.forename: Wojciech
authors.initials: W
authors.lastname: Grochala