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Lead-Free Hybrid Ferroelectric Material Based on the Formamidine: [NH2CHNH2]3Bi2I9.

Abstract

The extraordinary thermally stable up to around 600 K crystals of [NH2CHNH2]3Bi2I9 (FA3Bi2I9) have been grown with the use of 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 hysteresis loops observations. 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 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.

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Publication details

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
Citation: J. Mater. Chem. C, 2019, Accepted Manuscript

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    Lead-Free Hybrid Ferroelectric Material Based on the Formamidine: [NH2CHNH2]3Bi2I9.

    P. Szklarz, A. Gągor, R. Jakubas, P. Zielinski, A. Piecha-Bisiorek, J. Cichos, M. Karbowiak, G. Bator and A. Cizman, J. Mater. Chem. C, 2019, Accepted Manuscript , DOI: 10.1039/C8TC06458J

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