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Electron paramagnetic resonance study of ferroelectric phase transition and dynamic effects in a Mn doped [NH][Zn(HCOO)] hybrid formate framework. | LitMetric

AI Article Synopsis

  • The study investigates a manganese-doped hybrid framework with ferroelectric properties, showing significant changes in electron paramagnetic resonance (EPR) spectra at 190 K, the phase transition temperature.
  • The successful substitution of Zn2+ ions by Mn2+ is confirmed through various EPR techniques, revealing the influence of temperature on Mn2+ zero-field splitting and the structural changes of MnO6 octahedra during the transition.
  • Results from EPR and density functional theory calculations suggest a quasi two-dimensional ordering in the framework, with relaxation time analysis indicating that the dynamics are significantly influenced by vibrational modes of the metal-oxygen octahedra.

Article Abstract

We present an X- and Q-band continuous wave (CW) and pulse electron paramagnetic resonance (EPR) study of a manganese doped [NH4][Zn(HCOO)3] hybrid framework, which exhibits a ferroelectric structural phase transition at 190 K. The CW EPR spectra obtained at different temperatures exhibit clear changes at the phase transition temperature. This suggests a successful substitution of the Zn2+ ions by the paramagnetic Mn2+ centers, which is further confirmed by the pulse EPR and 1H ENDOR experiments. Spectral simulations of the CW EPR spectra are used to obtain the temperature dependence of the Mn2+ zero-field splitting, which indicates a gradual deformation of the MnO6 octahedra indicating a continuous character of the transition. The determined data allow us to extract the critical exponent of the order parameter (β = 0.12), which suggests a quasi two-dimensional ordering in [NH4][Zn(HCOO)3]. The experimental EPR results are supported by the density functional theory calculations of the zero-field splitting parameters. Relaxation time measurements of the Mn2+ centers indicate that the longitudinal relaxation is mainly driven by the optical phonons, which correspond to the vibrations of the metal-oxygen octahedra. The temperature behavior of the transverse relaxation indicates a dynamic process in the ordered ferroelectric phase.

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http://dx.doi.org/10.1039/d0cp01612hDOI Listing

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