Anomalous low-temperature behavior of the Co dimers in the oxo-halide CoSb2O3Br2
Anomalous low-temperature behavior of the Co dimers in the oxo-halide CoSb2O3Br2
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含氧卤化物 CoSb2O3Br2 中钴二聚体的异常低温行为
DOI：
10.1016/j.jssc.2008.07.005
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发表时间：
2008
影响因子：
3.3
通讯作者：
R. K. Kremer
中科院分区：
文献类型：
--
作者：
Z. Hugonin;M. Johnsson;S. Lidin;D. Wulferding;P. Lemmens;R. K. Kremer
报道了一种新型氧化溴化钴锑的合成、晶体结构测定、磁性和低温结构性能。CoSb{sub 2}O{sub 3}Br{sub 2}在空间群P-1的三斜晶系中结晶，晶格参数为：a=5.306(3) a, b=7.812(4) a, c=8.0626(10) a, {alpha}=88.54(3){sup O}, {beta}=82.17(3){sup O}, {gamma}=80.32(4){sup O}， Z=2。晶体结构由单晶x射线数据解出，细化为F{sup 2}， R{sub 1}=3.08。该结构由[CoO{sub 4}Br{sub 2}]、[SbO{sub 3}Br]和[SbO{sub 3}]三个单元组成，它们通过共享边角连接，形成Co-Co结构二聚体。这些层没有净电荷，仅通过范德华力与相邻层弱连接。在{约}25k以上，磁化率与磁场无关，可以用居里-魏斯定律很好地描述。在25k以下，磁化率达到最大值，然后再次下降，这是远程反铁磁相关开始的典型特征。在T{sub N}{约}9k以下观察到长程反铁磁有序，表明层内Co-Co二聚体之间存在大量的二聚体交换耦合。然而，根据热容结果，只有一小部分熵与长程有序跃迁有关。在T<6 K的拉曼散射中观测到的声子异常和比热异常表明，在最低温度下，结构不稳定导致了反演对称性的丧失。-图解摘要：报道了新型层状化合物CoSb{sub 2}O{sub 3}Br{sub 2}的合成、晶体结构测定和磁性能。结构Co-Co二聚体在层内形成。在25k以下的磁化率是远程反铁磁相关开始的典型特征。拉曼散射和比热测量都指出结构不稳定导致6 K以下反转对称性的损失。
We report the synthesis, crystal structure determination, magnetic and low-temperature structural properties of a new cobalt antimony oxo-bromide. CoSb{sub 2}O{sub 3}Br{sub 2} crystallizes in the triclinic crystal system, space group P-1, with the following lattice parameters: a=5.306(3) A, b=7.812(4) A, c=8.0626(10) A, {alpha}=88.54(3){sup o}, {beta}=82.17(3){sup o}, {gamma}=80.32(4){sup o}, and Z=2. The crystal structure was solved from single crystal X-ray data and refined on F{sup 2}, R{sub 1}=3.08. The structure consists of layers made up by three building blocks, [CoO{sub 4}Br{sub 2}], [SbO{sub 3}Br], and [SbO{sub 3}] that are connected via edge- and corner-sharing so that structural Co-Co dimers are formed. The layers have no net charge and are only weakly connected by van der Waals forces to adjacent layers. Above {approx}25 K the magnetic susceptibility is independent of the magnetic field and can be very well described by a Curie-Weiss law. Below 25 K the susceptibility passes through a maximum and decreases again that is typical for the onset of long-range antiferromagnetic correlations. Long-range antiferromagnetic ordering is observed below T{sub N}{approx}9 K indicating substantial inter-dimer exchange coupling between Co-Co dimers within the layers. However, according to the heat capacity results only a minute fraction of the entropy is associated with the long-range ordering transition. The phonon anomalies observed for T<6 K in Raman scattering and an anomaly in the specific heat point to a structural instability leading to a loss of inversion symmetry at lowest temperatures. - Graphical abstract: The synthesis, crystal structure determination, and magnetic properties of the new layered compound CoSb{sub 2}O{sub 3}Br{sub 2} is reported. Structural Co-Co dimers are formed within the layers. The susceptibility below 25 K is typical for the onset of long-range antiferromagnetic correlations. Raman scattering and specific heat measurements both point to a structural instability leading to a loss of inversion symmetry below 6 K.
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