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Issue 10, 2019
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Lead-free hybrid ferroelectric material based on formamidine: [NH2CHNH2]3Bi2I9

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The extraordinary thermal stability of [NH2CHNH2]3Bi2I9 (FA3Bi2I9) crystals, up to around 600 K, has been enhanced by using the evaporating method. DSC measurements have revealed reversible structural phase transitions: at 203 K (Phase I → Phase II), 173 K (II → III), 134.7 K (III → IV), 131.4 K (IV → V), and 120 K (V → VI). The crystal structures of FA3Bi2I9 adopt the polar space groups P63mc at 220 K (Phase I) and Cmc21 at 190 K (Phase II). The pyroelectric current (Ipyr) measured in the temperature range covering all the phases of FA3Bi2I9 confirmed their polar nature. The reversibility of the spontaneous polarization in each phase has been confirmed by the observed hysteresis loops. All the phase transitions are dielectrically active. The dielectric response (ε*(ω,T) close to 134.7 and 131.4 K) is characteristic of ferroelectrics with a critical slowing-down process. Optical bandgaps estimated from the UV-vis measurements and calculated using the DFT method are equal to 1.85 and 1.89 eV, respectively. On the basis of the structural, dielectric, and spectroscopic results, the molecular mechanisms of the phase transitions have been proposed.

Graphical abstract: Lead-free hybrid ferroelectric material based on formamidine: [NH2CHNH2]3Bi2I9

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The article was received on 21 Dec 2018, accepted on 04 Feb 2019 and first published on 04 Feb 2019

Article type: Paper
DOI: 10.1039/C8TC06458J
J. Mater. Chem. C, 2019,7, 3003-3014

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    Lead-free hybrid ferroelectric material based on formamidine: [NH2CHNH2]3Bi2I9

    P. Szklarz, A. Gągor, R. Jakubas, P. Zieliński, A. Piecha-Bisiorek, J. Cichos, M. Karbowiak, G. Bator and A. Ciżman, J. Mater. Chem. C, 2019, 7, 3003
    DOI: 10.1039/C8TC06458J

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