Reinvestigation of crystal structure and structural disorder of Ba3MgSi2O8
Reinvestigation of crystal structure and structural disorder of Ba3MgSi2O8
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DOI：
10.1154/1.3193522
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发表时间：
2009-09
影响因子：
0.5
通讯作者：
T. Iwata;T. Horie;K. Fukuda
中科院分区：
文献类型：
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作者：
T. Iwata;T. Horie;K. Fukuda
用实验室X射线粉末衍射重新研究了Ba_3MgSi_2O_8的晶体结构和结构无序。标题化合物为三方晶系，空间群为P3m1，Z=1，晶胞参数a= 0.561453（4）nm，c= 0.727629（4）nm，V= 0.198641（2）nm3。用于结构细化的初始结构模型取自钾芒硝（K3NaS2O8），并通过分裂原子模型进行修改。在分裂原子模型中，两种类型的Ba网站和SiO4四面体之一，分别，位置和取向无序。用Rietveld方法对新的晶体结构和结构无序进行了修正。基于最大熵方法的模式拟合（MPF）方法被用来确认分裂原子模型的有效性，在该模型中，由假设强度划分引起的传统结构偏差被最小化。由MPF计算的最终可靠性指标为Rwp= 6.52%，S = 1.36，Rp = 4.84%，RB = 0.97%，RF = 0.52%。Ba_3MgSi_2O_8的无序结构的详细信息显示在MPF测定的三维和二维电子密度分布图中。
Crystal structure and structural disorder of Ba3MgSi2O8 were reinvestigated by laboratory X-ray powder diffraction. The title compound was found to be trigonal with space group P3m1, Z=1, and unit-cell dimensions a=0.561 453(4) nm, c=0.727 629(4) nm, and V=0.198 641(2) nm3. The initial structural model used for structure refinement was taken from that of glaserite (K3NaS2O8) and modified by a split-atom model. In the split-atom model, one of the two types of Ba sites and that of SiO4 tetrahedra were, respectively, positionally and orientationally disordered. The new crystal structure and structural disorder were refined by the Rietveld method. The maximum-entropy-method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The final reliability indices calculated from MPF were Rwp=6.52%, S=1.36, Rp=4.84%, RB=0.97%, and RF=0.52%. Details of the disorder structure of Ba3MgSi2O8 are shown in the three-dimensional and two-dimensional electron-density distribution maps determined by MPF.