Laboratoire CRISMAT, UMR 6508 CNRS, ENSICAEN, 6 bd du Maréchal Juin, 14050 Caen Cedex 4, France.
Inorg Chem. 2013 May 20;52(10):6073-82. doi: 10.1021/ic400426m. Epub 2013 May 8.
On the basis of the Mn(3+) for Fe(3+) substitution in Pb(2-x)Ba(x)Fe2O5, a novel oxide Pb1.3Ba0.7MnFeO5 has been synthesized at normal pressure. Though it belongs to the same structural family, the mixed "MnFe" oxide exhibits a very different structural distortion of its framework compared to the pure "Fe2" oxide, due to the Jahn-Teller effect of Mn(3+). Combined neutron diffraction, high resolution electron microscopy/high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) investigations allow the origin of this difference to be determined. Here we show that the MO6 octahedra of the double perovskite layers in the "MnFe" structure exhibit a strong tetragonal pyramidal distortion "5 + 1", whereas the "Fe2" structure shows a tetrahedral distortion "4 + 2" of the FeO6 octahedra. Similarly, the MO5 polyhedra of the "MnFe" structure tend toward a tetragonal pyramid, whereas the FeO5 polyhedra of the "Fe2" structure are closer to a trigonal bipyramid. Differently from the oxide Pb(2-x)Ba(x)Fe2O5, which is antiferromagnetic, the oxide Pb1.3Ba0.7MnFeO5 exhibits a spin glass behavior with Tg ∼ 50 K in agreement with the disordered distribution of the Mn(3+) and Fe(3+) species.
在 Mn(3+)取代 Fe(3+)的基础上，在常压下合成了一种新型氧化物 Pb1.3Ba0.7MnFeO5。尽管它属于相同的结构家族，但混合的“MnFe”氧化物与纯“Fe2”氧化物相比，其框架的结构变形非常不同，这是由于 Mn(3+)的 Jahn-Teller 效应。结合中子衍射、高分辨率电子显微镜/高角度环形暗场扫描透射电子显微镜（HAADF-STEM）研究，可以确定这种差异的起源。在这里，我们表明，“MnFe”结构中双钙钛矿层的 MO6 八面体表现出强烈的四方金字塔畸变“5 + 1”，而“Fe2”结构则表现出 FeO6 八面体的四面体畸变“4 + 2”。类似地，“MnFe”结构的 MO5 多面体趋于四方金字塔，而“Fe2”结构的 FeO5 多面体更接近三角双锥。与反铁磁氧化物 Pb(2-x)Ba(x)Fe2O5 不同，氧化物 Pb1.3Ba0.7MnFeO5 表现出自旋玻璃行为，Tg ∼ 50 K，与 Mn(3+)和 Fe(3+)物种的无序分布一致。
