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首页> 外文期刊>Powder diffraction >Improved structural model of Pb-doped γ-Bi_2O_3: (Bi_(23.68)Pk_(0.32))(Bi_(1.28)Pb_(0.72))O_(38.48)
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Improved structural model of Pb-doped γ-Bi_2O_3: (Bi_(23.68)Pk_(0.32))(Bi_(1.28)Pb_(0.72))O_(38.48)

机译：掺杂Pb的γ-Bi_2O_3的改进结构模型：（Bi_（23.68）Pk_（0.32））（Bi_（1.28）Pb_（0.72））O_（38.48）

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摘要

A polycrystalline single-phase sample with nominal composition Bi_(24)PbO_(37) was synthesized from Bi_2O_3 and PbO by a high-temperature solid state reaction at 690℃ for 1.5 h. The compound adopts Bi_(12)SiO_(20)-type structure [cubic, space group I23 (No. 197); a-10.24957(3) A] and was refined to R_p = 7.96%, R_(wp)= 10.4%, R_(exp) = 8.43%, R_B = 3.06%, and S= 1.23. The distributions of Pb~(2+) and Bi~(3+) over cationic sites based on the X-ray powder diffraction data were determined using a combination of the Rietveld refinement and bond valence calculations. The results showed that the asymmetric unit contains two mixed cation sites: the fully occupied 24/site and the partly occupied 8c site, with the unit-cell content (Bi_(23.68)Pb_(0.32))(Bi_(1.28)Pb_(0.72))O_(38.48). The structural constraints favor a preference of Pb~(2+) ion for the 8c site, i.e. only 1.3% of Bi~(3+) is substituted by Pb~(2+) at the 24/site and 36% at the 8c site. At the 24/site, the cations are surrounded by 5 + 2 or in a very small amount by 5 + 1 + 2 oxide ions, forming a base bicapped square pyramid or a bicapped highly deformed octahedron, respectively. At the 8c site, the cations with three oxide ions form a trigonal pyramid with the cations at the apex.
机译：通过Bi_2O_3和PbO在690℃下高温固相反应1.5 h，合成了标称成分为Bi_（24）PbO_（37）的多晶单相样品。该化合物采用Bi_（12）SiO_（20）型结构[立方，空间群I23（第197号）； a-10.24957（3）A]并细化为R_p = 7.96％，R_（wp）= 10.4％，R_（exp）= 8.43％，R_B = 3.06％，S = 1.23。基于X射线粉末衍射数据，结合Rietveld精制和键合价计算确定了Pb〜（2+）和Bi〜（3+）在阳离子位点上的分布。结果表明，不对称单元包含两个混合阳离子位点：完全占据的24 /位点和部分占据的8c位点，单元格含量为（Bi_（23.68）Pb_（0.32））（Bi_（1.28）Pb_（0.72 ））O_（38.48）。结构约束有利于Pb〜（2+）离子对8c位点的偏爱，即，只有1.3％的Bi〜（3+）被24b /位的Pb〜（2+）和36％的8c位点所取代。现场。在24个位点，阳离子被5 + 2包围，或极少量地被5 +1 + 2个氧化物离子包围，分别形成了一个基本的二头方形金字塔或二头形高度变形的八面体。在8c位置，带有三个氧化物离子的阳离子与阳离子在顶点形成一个三角金字塔。

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