title: Effect of solvent, temperature and pressure on the stability of chiral and perovskite metal formate frameworks of [NH2NH3][M(HCOO)3] (M = Mn, Fe, Zn).
abstract: We report the synthesis, crystal structure, and thermal, Raman, infrared and magnetic properties of [NH2NH3][M(HCOO)3] (HyM) compounds (M = Mn, Zn, Fe). Our results show that synthesis from methanol solution leads to perovskite polymorphs while that from 1-methyl-2-pyrrolidinone or its mixture with methanol allows obtaining chiral polymorphs. Perovskite HyFe, chiral HyFe and chiral HyMn undergo phase transitions at 347, 336 and 296 K, respectively, with symmetry changes from Pnma to Pna21, P63to P212121and P63to P21. X-ray diffraction and Raman studies show that the phase transitions are governed by dynamics of the hydrazinium ions. Low-temperature magnetic studies show that these compounds exhibit magnetic ordering below 9-12.5 K. Since the low-temperature structures of chiral HyMn and perovskite HyFe are polar, these compounds are possible multiferroic materials. We also report high-pressure Raman scattering studies of chiral and perovskite HyZn, which show much larger stiffness of the latter phase. These studies also show that the ambient pressure polar phases are stable up to at least 1.4 and 4.1 GPa for the chiral and perovskite phase, respectively. Between 1.4 and 2.0 GPa (for chiral HyZn) and 4.1 and 5.2 GPa (for perovskite HyZn) pressure-induced transitions are observed associated with changes in the zinc-formate framework. Strong broadening of Raman bands and the decrease in their number for the high-pressure phase of chiral HyZn suggest that this phase is disordered and has higher symmetry than the ambient pressure one.
authors.affiliation: Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Box 1410, 50-950 Wrocław 2, Poland. m.maczka@int.pan.wroc.pl.
authors.forename: Mirosław
authors.initials: M
authors.lastname: Mączka
authors.affiliation: Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Box 1410, 50-950 Wrocław 2, Poland. m.maczka@int.pan.wroc.pl.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Pasińska
authors.affiliation: Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Box 1410, 50-950 Wrocław 2, Poland. m.maczka@int.pan.wroc.pl.
authors.forename: Maciej
authors.initials: M
authors.lastname: Ptak
authors.affiliation: Faculdade de Física, Universidade Federal do Pará, 66075-110, Belém, PA, Brazil.
authors.forename: Waldeci
authors.initials: W
authors.lastname: Paraguassu
authors.affiliation: Faculdade de Física, Universidade Federal do Pará, 66075-110, Belém, PA, Brazil.
authors.forename: Tercio Almeida
authors.initials: TA
authors.lastname: da Silva
authors.affiliation: Department of Experimental Physics, Wrocław University of Technology, Wybrzeże Wyspiańskiego 27, 50-370, Wrocław, Poland.
authors.forename: Adam
authors.initials: A
authors.lastname: Sieradzki
authors.affiliation: Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Box 1410, 50-950 Wrocław 2, Poland. m.maczka@int.pan.wroc.pl.
authors.forename: Adam
authors.initials: A
authors.lastname: Pikul