Jump to main content
Jump to site search

Issue 18, 2017
Previous Article Next Article

Electron paramagnetic resonance and electric characterization of a [CH3NH2NH2][Zn(HCOO)3] perovskite metal formate framework

Author affiliations

Abstract

We present a combined continuous-wave (CW) and pulse electron paramagnetic resonance (EPR), pulse electron-nuclear double resonance (ENDOR), pyrocurrent as well as broadband dielectric study of a [CH3NH2NH2][Zn(HCOO)3] dense perovskite metal–organic framework (MOF). The pyroelectric current of a single crystal sample reveals two structural phase transitions at Tc1 = 325 and Tc2 = 173 K that are related to the ordering of CH3NH2NH2+ cations. The dielectric permittivity exhibits a small kink at Tc1 implying improper ferroelectric phase transition, while much stronger anomaly is observed at Tc2. The dielectric spectra of the intermediate phase reveal a Cole–Cole relaxation process that is assigned to the hopping motion of the CH3NH2NH2+ cations. EPR and ENDOR experiments are performed on powder MOF samples doped with small amounts of paramagnetic Mn2+ and Cu2+ probe ions. CW EPR spectra reveal the successful incorporation of these ions at the Zn2+ lattice sites, while ENDOR measurements indicate several proton species that are in excellent agreement with the X-ray diffraction data. The CW EPR linewidth and intensity of the Mn2+ spectra demonstrate anomalies at the phase transition points. The direct measurements of the phase memory time Tm of the Mn2+ centers indicate a second motional process of CH3NH2NH2+ cations below Tc2. The measurements of the longitudinal relaxation time T1 of the low-temperature phase reveal a coupling between the electron spins and a hard optical phonon mode which undergoes a damping due to the coupling with the relaxational mode as Tc2 is approached. The temperature dependent Mn2+ and Cu2+ spectra reflect the structural changes of the metal–oxygen octahedra. The fine structure splitting of Mn2+ ions is increasing as the temperature is decreased reflecting a distortion of the MnO6 octahedra. The Cu2+ hyperfine interaction demonstrates a first-order character close to the tricritical limit of the phase transition at Tc2.

Graphical abstract: Electron paramagnetic resonance and electric characterization of a [CH3NH2NH2][Zn(HCOO)3] perovskite metal formate framework

Back to tab navigation

Supplementary files

Publication details

The article was received on 17 Mar 2017, accepted on 05 Apr 2017 and first published on 06 Apr 2017


Article type: Paper
DOI: 10.1039/C7TC01140G
Citation: J. Mater. Chem. C, 2017,5, 4526-4536
  •   Request permissions

    Electron paramagnetic resonance and electric characterization of a [CH3NH2NH2][Zn(HCOO)3] perovskite metal formate framework

    M. Šimėnas, S. Balčiūnas, M. Trzebiatowska, M. Ptak, M. Mączka, G. Völkel, A. Pöppl and J. Banys, J. Mater. Chem. C, 2017, 5, 4526
    DOI: 10.1039/C7TC01140G

Search articles by author

Spotlight

Advertisements