Synthesis, structure and magnetic ordering of the mullite-type Bi2Fe(4-x)CrxO9 solid solutions with a frustrated pentagonal Cairo lattice.
Synthesis, structure and magnetic ordering of the mullite-type Bi2Fe(4-x)CrxO9 solid solutions with a frustrated pentagonal Cairo lattice.
复制标题
具有受抑五方开罗晶格的莫来石型 Bi2Fe(4-x)CrxO9 固溶体的合成、结构和磁有序性。
DOI：
10.1039/c5dt04296h
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发表时间：
2016
影响因子：
4
通讯作者：
A. Abakumov
中科院分区：
文献类型：
--
作者：
M. G. Rozova;V. Grigoriev;I. Bobrikov;D. Filimonov;K. Zakharov;O. Volkova;A. Vasiliev;E. Antipov;A. Tsirlin;A. Abakumov
采用软化学技术，在氩气中进行固相反应，合成了高度均匀的摩尔来石型固溶体Bi2Fe(4-x)CrxO9 （x = 0.5, 1,1.2）。采用x射线和中子粉末衍射、透射电镜和（57）Fe Mössbauer光谱(S.G. pam, a = 7.95579(9) Å， b = 8.39145(9) Å， c = 5.98242（7) Å， RF（x射线）= 0.022，RF（中子）= 0.057）研究了Bi2Fe3CrO9的晶体结构。该结构的ab平面由三个四面体配位的Fe位点和两个八面体配位的Fe/Cr位点组成的扭曲的五边形环镶嵌而成，它们在ab平面上通过共享角连接在一起，形成一个五边形Cairo晶格。磁化率测量和粉末中子衍射表明，当Cr含量从x = 0时的TN ~ 250 K增加到x = 1.2时的TN ~ 155 K时，n<s:1>温度降低，化合物呈反铁磁有序（AFM）。在T = 30 K时，Bi2Fe3CrO9的磁性结构表征为传播矢量K =(1/2,1/2,1/2)。四面体配位铁离子在共用角四面体的二聚体内形成单线态对，但相邻二聚体上的自旋几乎是正交的。八面体配位的（Fe,Cr）阳离子沿c平面形成反铁磁性的上-上-下-下链，而ab平面的自旋排列近邻之间几乎正交，次近邻之间共线。所得到的磁性结构与纯Bi2Fe4O9中的磁性结构明显不同，甚至在晶体等效交换中也具有几种类型的自旋相关，这可能是由铁和铬同时存在于八面体位置引起的。
Highly homogeneous mullite-type solid solutions Bi2Fe(4-x)CrxO9 (x = 0.5, 1, 1.2) were synthesized using a soft chemistry technique followed by a solid-state reaction in Ar. The crystal structure of Bi2Fe3CrO9 was investigated using X-ray and neutron powder diffraction, transmission electron microscopy and (57)Fe Mössbauer spectroscopy (S.G. Pbam, a = 7.95579(9) Å, b = 8.39145(9) Å, c = 5.98242(7) Å, RF(X-ray) = 0.022, RF(neutron) = 0.057). The ab planes in the structure are tessellated with distorted pentagonal loops built up by three tetrahedrally coordinated Fe sites and two octahedrally coordinated Fe/Cr sites, linked together in the ab plane by corner-sharing forming a pentagonal Cairo lattice. Magnetic susceptibility measurements and powder neutron diffraction show that the compounds order antiferromagnetically (AFM) with the Néel temperatures decreasing upon increasing the Cr content from TN ∼ 250 K for x = 0 to TN ∼ 155 K for x = 1.2. The magnetic structure of Bi2Fe3CrO9 at T = 30 K is characterized by a propagation vector k = (1/2,1/2,1/2). The tetrahedrally coordinated Fe cations form singlet pairs within dimers of corner-sharing tetrahedra, but spins on the neighboring dimers are nearly orthogonal. The octahedrally coordinated (Fe,Cr) cations form antiferromagnetic up-up-down-down chains along c, while the spin arrangement in the ab plane is nearly orthogonal between nearest neighbors and collinear between second neighbors. The resulting magnetic structure is remarkably different from the one in pure Bi2Fe4O9 and features several types of spin correlations even on crystallographically equivalent exchange that may be caused by the simultaneous presence of Fe and Cr on the octahedral site.