Temperature evolution of (quinuclidinium)[FeCl]: a plastic/polar magnetic hybrid compound with a giant dielectric constant

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2020-09, Vol.8 (33), p.11389-11398
• Main Authors: González-Izquierdo, Palmerina, Fabelo, Oscar, Canadillas-Delgado, Laura, Beobide, Garikoitz, Vallcorba, Oriol, Sánchez-Andújar, Manuel, Fernández-Díaz, María Teresa, de Pedro, Imanol
• Format: Article
• Language: English
• Subjects: Broken symmetry; Crystallography; Evolution; Ferrimagnetism; Ferromagnetism; Ion currents; Magnetic structure; Magnetic transitions; Neutron diffraction; Neutrons; Permittivity; Phase transitions; Physical properties; Single crystals; Synchrotron radiation; Temperature; Thermal analysis; Unit cell; X ray powder diffraction
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d0tc02341h

The temperature evolution of the physical properties of the (quinuclidinium)[FeCl 4 ] compound shows an unprecedented series of phase, structural and magnetic transitions. Above 390 K, a plastic phase (also termed as "rotator phases") is observed (phase I). Between 390 K and 280 K, an intermediate phase solved in a non-centrosymmetric space group has been characterized. Crystallographic studies show that the compound crystallizes in the Pbc 2 1 polar space group (phase II), and therefore the phase transition between I and II involves a paraelectric-to-polar phase transition. This result is confirmed by complex dielectric permittivity. Moreover, the real part of the dielectric permittivity shows a giant increase above 390 K, reaching a maximum value of 10 5 that is notably larger than any other hybrid compound previously reported. Below 280 K, a third structural phase transition is observed, which involves the doubling of the unit cell and a change of symmetry due to the blocking of counter-ions, phase III crystallizing in the Pbca centrosymmetric space group. Below 3.5 K, long-range magnetic order is detected. Neutron diffraction below this order temperature suggests breaking of symmetry and the magnetic structure in phase IV was solved in the P 2 1 ′2 1 ′2 1 Shubnikov space group, giving rise to a ferrimagnetic structure that allows a net ferromagnetic signal along the c -axis. The temperature evolution of (quinuclidinium)[FeCl 4 ] shows the occurrence of an intricate series of phase transitions, involving notable modifications on the physical properties.