Structural, thermal, dielectric and phonon properties of perovskite-like imidazolium magnesium formate.

Mirosław Mączka,Adam Sieradzki,Anna Gągor,Jerzy Hanuza,Waldeci Paraguassu,Nathalia Leal Marinho Costa

doi:10.1039/c6cp01353h

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.

Highlights

University of Economics, 118/120 Komandorska Str., 53-345 Wrocław, Poland † Electronic supplementary information (ESI) available: Tables S1–S5: crystal data for imidazolium magnesium formate (ImMg), IR and Raman wavenumber for the low- and high-temperature phases of ImMg together with the proposed assignment, and wavenumber intercepts at zero pressure and pressure coefficients for ambient and high-pressure phases of ImMg
DSC The DSC measurements show that ImMg exhibits a phase transition at 451 K upon heating and 448 K upon cooling (Fig. S1, ESI†)
We report the synthesis and characterization of ImMg perovskite-type formate

Summary

Introduction

University of Economics, 118/120 Komandorska Str., 53-345 Wrocław, Poland † Electronic supplementary information (ESI) available: Tables S1–S5: crystal data for ImMg, IR and Raman wavenumber for the low- and high-temperature phases of ImMg together with the proposed assignment, and wavenumber intercepts at zero pressure and pressure coefficients for ambient and high-pressure phases of ImMg. The most evident difference between the high- and low-temperature patterns detected for ImMg and ImMn is the vanishing of the (À1À11), (À111), (1À11) and (111) diffraction peaks after the phase transition, signifying the reduction of the unit cell size.

Results

Conclusion