title: Experimental and theoretical studies of structural phase transition in a novel polar perovskite-like [C2H5NH3][Na0.5Fe0.5(HCOO)3] formate.
abstract: We report the synthesis, single crystal X-ray diffraction, and thermal, dielectric, Raman and infrared studies of a novel heterometallic formate [C2H5NH3][Na0.5Fe0.5(HCOO)3] (EtANaFe). The thermal studies show that EtANaFe undergoes a second-order phase transition at about 360 K. X-ray diffraction data revealed that the high-temperature structure is monoclinic, space group P2(1)/n, with dynamically disordered ethylammonium (EtA(+)) cations. EtANaFe possesses a polar low-temperature structure with the space group Pn and, in principle, is ferroelectric below 360 K. Dielectric data show that the reciprocal of the real part of dielectric permittivity above and below the phase transition temperature follows the Curie-Weiss, as expected for a ferroelectric phase transition. Based on theoretical calculations, we estimated the polarization as (0.2, 0, 0.8) μC cm(-2), i.e., lying within the ac plane. The obtained data also indicate that the driving force of the phase transition is ordering of EtA(+) cations. However, this ordering is accompanied by significant distortion of the metal formate framework.
authors.affiliation: Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Box 1410, 50-950 Wrocław 2, Poland. m.ptak@int.pan.wroc.pl.
authors.forename: Maciej
authors.initials: M
authors.lastname: Ptak
authors.forename: Mirosław
authors.initials: M
authors.lastname: Mączka
authors.forename: Anna
authors.initials: A
authors.lastname: Gągor
authors.forename: Adam
authors.initials: A
authors.lastname: Sieradzki
authors.forename: Alessandro
authors.initials: A
authors.lastname: Stroppa
authors.forename: Domenico
authors.initials: D
authors.lastname: Di Sante
authors.forename: Juan Manuel
authors.initials: JM
authors.lastname: Perez-Mato
authors.forename: Lucyna
authors.initials: L
authors.lastname: Macalik