钾水钠锰矿单晶的结构调制
Structural modulation in potassium birnessite single crystals
摘要：
我们报告的单晶钾水钠锰矿（K0.31MnO2*0.41H2O）的生长，并提出了这挫磁系统的平均和局部结构表征。采用助熔剂生长法，在700 °C下用KNO 3/B2 O3助熔剂获得单晶。单晶X-射线衍射表明其具有平均正交对称性，空间群为Cmcm。高角度环形暗场扫描透射电子显微镜（HAADF-STEM）与原子分辨率能量色散X射线光谱（EDS）的组合证明了钾水钠锰矿的层状结构，其中含锰平面被钾原子层很好地分隔开。MnO 6八面体和K/H2O平面通过积分微分相衬（iDPC）STEM清晰成像。此外，iDPC-STEM还揭示了具有氧化锰平面的交替对比度的局部域的存在，最有可能源自Mn 3+和Mn 4+沿c轴的电荷排序。这些电荷有序域明显相关的c-晶格参数相比，矩阵的其余部分减少。从这项工作中获得的见解可以更好地理解结构和磁性之间的相关性。
英文摘要：
We report on the growth of single-crystal potassium birnessite (K0.31MnO2*0.41H2O) and present both the average and local structural characterization of this frustrated magnetic system. Single crystals were obtained employing a flux growth method with a KNO3/B2O3 flux at 700 °C. Single-crystal X-ray diffraction revealed an average orthorhombic symmetry, with space group Cmcm. A combination of high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with atomic resolution energy dispersive X-ray spectroscopy (EDS) demonstrated the layered structure of potassium birnessite with manganese-containing planes well separated by layers of potassium atoms. MnO6 octahedra and the K/H2O planes were clearly imaged via integrated differential phase contrast (iDPC) STEM. Furthermore, iDPC-STEM also revealed the existence of local domains with alternating contrast of the manganese oxide planes, most likely originating from charge ordering of Mn3+ and Mn4+ along the c-axis. These charge-ordered domains are clearly correlated with a reduction in the c-lattice parameter compared to the rest of the matrix. The insight gained from this work allows for a better understanding of the correlation between structure and magnetic properties.
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