Crystal and Magnetic Structures of High Pressure Perovskite-Type Oxyfluorides,PbFeO 2 F and 0.5PbFeO 2 F-0.5PbTiO 3 [Pb(
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0988-QQ06-03
Crystal and Magnetic Structures of High pressure Perovskite-Type Oxyfluorides,PbFeO2F and 0.5PbFeO2F-0.5PbTiO3 [Pb(Fe0.5Ti0.5)O2.5F0.5] Tetsuhiro Katsumata1, Akihiro Takase1, Masashi Yoshida1, Yoshiyuki Inaguma1, John E. Greedan2, Jacques Barbier2, Lachlan M. D. Cranswick3, and Mario Bieringer4 1
Faculty of Science, Gakushuin Univ., 1-5-1 Mejiro, Toshima-ku, Tokyo, 171-8588, Japan
2
Chemistry department and Brockhouse Institute for Materials Research, McMaster Univ., 1280 Main Street West, Hamilton, L8S 4M1, Canada
3
Canadian Neutron Bean Center, Building 459, Chalk River Laboratories, Chalk River, K0J 1J0, Canada
4
Department of Chemistry, University of Manitoba, 506 Parker Building, Winnipeg, R3T 2N2, Canada
Abstract The perovskites PbFeO2F and 0.5PbFeO2F-0.5PbTiO3 were synthesized at high temperatures (1000 oC) and high pressures (4 – 6 GPa). The crystal and magnetic structures were determined using powder neutron diffraction. Quenched PbFeO2F has the cubic perovskite-type, Pm3m, structure in which the Pb ion shifts from ideal A-site along the directions, which is in good accordance with a previous report. The magnetic structure is antiferromagnetic G-type with propagation vector k = (1/2 1/2 1/2) and an Fe3+ ordered moment of 3.83 µB at 283K. The Néel temperature is 655(5) K. Annealed PbFeO2F has a tetragonal perovskite-type structure at room temperature and transforms reversibly from tetragonal to cubic at approximately 470 K. A superlattice with dimensions a × a × 5c is observed both in electron and x-ray diffraction. The solid solution 0.5PbFeO2F-0.5PbTiO3 belongs to the non-centrosymmetric space group P4mm. The magnetic structure is G-type antiferromagnetic and shows a weak ferromagnetic moment at 4 K. Consequently, 0.5PbFeO2F-0.5PbTiO3 is simultaneously ferroelectric and a weak ferromagnet at low temperature. The Nèel temperature is 450 K but the temperature dependence of the ordered Fe moment is anomalous. Introduction Multi-ferroic materials, in which the ferroelectricity and ferromagnetism are present in the same material, have received renewed interest in recent years. Many multiferroic compounds are found in the transition metal oxides, especially with the perovskite-type structure such as, BiMnO3 [1], BiFeO3 [2], Bi2FeCrO6 [3], Bi2NiMnO6 [4], TbMnO3 and DyMnO3 [5]. In BiMO3 compounds, the 6s lone pair of Bi ion and 3d transition metal ion in B-site induce the ferroelectric and ferromagnetic, respectively. The perovskite-type oxyfluoride, PbFeO2F is considered to be a candidate multiferroic material, because this compound has similar features to BiMO3, i.e. the A-site ion has a 6s lone pair and the B-site is occupied by a 3d transition metal ion. PbFeO2F was synthesized under high pressure and high temperature by Troyanchuk et al. [6]. Our group has been interested in this compound and has been successful in preparing a high purity sample. Furthermore, it was found that this
compound has a cubic perovskite-type structure in which the Pb ion shits from the ideal A-site position a
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