화학공학소재연구정보센터
Inorganic Chemistry, Vol.55, No.9, 4354-4361, 2016
Common Building Motifs in Ba2Fe3(PO4)(4)center dot 2H(2)O, BaFe3(PO4)(3), and Na3Fe3(PO4)(4): Labile Fe2+/Fe3+ Ordering and Charge-Dependent Magnetism
Two new mixed-valence Fe2/3+ barium phosphates have been synthesized in hydrothermal conditions and characterized: Ba2Fe32.66+(PO4)(4).2H(2)O (compound 1, ratio Fe3+/Fe2+ = 2:1, orthorhombic space group Pbca, a = 6.71240(10) angstrom, b = 10.6077(2) angstrom, c = 20.9975(5) angstrom, R1 = 3.39%) and BaFe32.33+(PO4)(3) (compound 2, ratio Fe3+/Fe2+ = 1:2, orthorhombic, space group Imma with a = 10.5236(3) angstrom, b = 13.4454(4) angstrom, c = 6.6411(2) angstrom, R1 = 1.63%). 1 has a two-dimensional crystal structure built of [Fe2.5+2Fe3+1(PO4)4]4 layers with charge segregation on two individual Fe crystal sites, in contrast to the single valence on these two sites found in similar layers of Na3Fe3+3(PO4)4. The crystal structure of 2 is formed of the same layers but condensed into a 3D [Fe(2+)2Fe(3+) (1)(PO4)(3)](2-) framework. The complete Fe2+ vs Fe3+ charge ordering on the two available sites differs from what was found in the two previous cases and denotes a remarkable charge adaptability of the common elementary units. Compared to the antiferromagnetic Na3Fe33+(PO4)(4) the partial iron reduction into Fe2+ is responsible for strong ferromagnetic components along the c-easy axis for both 1 and 2. Additionally 1 shows multiple magnetization steps in the perpendicular direction, giving raise to atypical anisotropic magnetism into a complex magnetic phase diagram.