RESUMO
SrFe0.75Mo0.25O3-δ has been recently discovered as an extremely efficient electrode for intermediate temperature solid oxide fuel cells (IT-SOFCs). We have performed structural and magnetic studies to fully characterize this multifunctional material. We have observed by powder neutron diffraction (PND) and transmission electron microscopy (TEM) that its crystal symmetry is better explained with a tetragonal symmetry (I4/mcm space group) than with the previously reported orthorhombic symmetry (Pnma space group). The temperature dependent magnetic properties indicate an exceptionally high magnetic ordering temperature (TN â¼ 750 K), well above room temperature. The ordered magnetic structure at low temperature was determined by PND to be an antiferromagnetic coupling of the Fe cations. Mössbauer spectroscopy corroborated the PND results. A detailed study, with X-ray absorption spectroscopy (XAS), in agreement with the Mössbauer results, confirmed the formal oxidation states of the cations to be mixed valence Fe(3+/4+) and Mo(6+).
RESUMO
[Pt(NCO)2(C12H12N2)], Mr = 463.37, orthorhombic, Cmc2(1), a = 18.722 (6), b = 11.889 (5), c = 6.688 (5) A, V = 1488.7 (9) A3, Z = 4, Dx = 2.067 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 90.59 cm-1, F(000) = 864, T = 291 (1) K, R = 0.052 for 735 reflections with F greater than or equal to 6 sigma F. The structure consists of square-planar coordinated Pt atoms, surrounded by four N atoms; of these, two belong to the bidentate bipyridyl ligand and two belong to the two pseudohalide groups which occupy cis positions. The bite angle of the bipyridyl ligand is 82.3 (9) degrees, significantly larger than the value reported earlier for the unsubstituted bipyridyl ligand, 76 (2) degrees. The metal atom is displaced 0.10 (5) A below the plane of the four N atoms. The non-bonding Pt-Pt distance is 0.258 (5) A longer in the title compound than in the unsubstituted ligand complex, leading to significant differences in the chemical and spectroscopic properties of the two homologues.
