title: Structural, thermal, dielectric and phonon properties of perovskite-like imidazolium magnesium formate.
abstract: We report the synthesis and characterisation of a magnesium formate framework templated by protonated imidazole. Single-crystal X-ray diffraction data showed that this compound crystallizes in the monoclinic structure in the P21/n space group with lattice parameters a = 12.1246(4) Å, b = 12.2087(5) Å, c = 12.4991(4) Å and β = 91.39(1)°. The antiparallel arrangement of the dipole moments associated with imidazolium cations suggests the antiferroelectric character of the room-temperature phase. The studied compound undergoes a structural phase transition at 451 K associated with a halving of the c lattice parameter and the disappearance of the antiferroelectric order. The monoclinic symmetry is preserved and the new metrics are a = 12.261(7) Å, b = 12.290(4) Å, c = 6.280(4) Å, and β = 90.62(5)°. Raman and IR data are consistent with the X-ray diffraction data. They also indicate that the disorder of imidazolium cations plays a significant role in the mechanism of the phase transition. Dielectric data show that the phase transition is associated with a relaxor nature of electric ordering. We also report high-pressure Raman scattering studies of this compound that revealed the presence of two pressure-induced phase transitions near 3 and 7 GPa. The first transition is most likely associated with a rearrangement of the imidazolium cations without any significant distortion of these cations and the magnesium formate framework, whereas the second transition leads to strong distortion of both the framework and imidazolium cations. High-pressure data also show that imidazolium magnesium formate does not show any signs of amorphization up to 11.4 GPa.
authors.affiliation: Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Box 1410, 50-950 Wrocław 2, Poland. m.maczka@int.pan.wroc.pl.
authors.forename: Mirosław
authors.initials: M
authors.lastname: Mączka
authors.affiliation: Faculdade de Física, Universidade Federal do Pará, 66075-110, Belém, PA, Brazil.
authors.forename: Nathalia Leal
authors.initials: NL
authors.lastname: Marinho Costa
authors.affiliation: Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Box 1410, 50-950 Wrocław 2, Poland. m.maczka@int.pan.wroc.pl.
authors.forename: Anna
authors.initials: A
authors.lastname: Gągor
authors.affiliation: Faculdade de Física, Universidade Federal do Pará, 66075-110, Belém, PA, Brazil.
authors.forename: Waldeci
authors.initials: W
authors.lastname: Paraguassu
authors.affiliation: Department of Experimental Physics, Wrocław University of Technology, Wybrzeże Wyspiańskiego 27, 50-370, Wrocław, Poland.
authors.forename: Adam
authors.initials: A
authors.lastname: Sieradzki
authors.affiliation: Department of Bioorganic Chemistry, Faculty of Industry and Economics, Wrocław University of Economics, 118/120 Komandorska Str., 53-345 Wrocław, Poland.
authors.forename: Jerzy
authors.initials: J
authors.lastname: Hanuza