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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Neutron diffraction and multinuclear solid state NMR investigation into the structures of oxide ion conducting La9.6Si6O26.4 and La8Sr2Si6O26, and their hydrated phases
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Neutron diffraction and multinuclear solid state NMR investigation into the structures of oxide ion conducting La9.6Si6O26.4 and La8Sr2Si6O26, and their hydrated phases

机译：中子衍射和多核固态NMR研究氧化物离子传导La9.6Si6O26.4和La8Sr2Si6O26的结构及其水合相

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Apatite silicates are attracting significant interest as potential SOFC electrolyte materials. They are non-conventional oxide ion conductors in the sense that oxide ion interstitials, rather than vacancies, are the key defects. In this work we compare the structures of La9.6Si6O26.4 and La8Sr2Si6O26, both before and after hydration in order to gather information about the location of the interstitial oxide ion site. Neutron diffraction structural studies suggest that in the as-prepared La8Sr2Si6O26 and hydrated La8Sr2Si6O26, the interstitial oxide ion sites are close to the apatite channel centre. For La9.6Si6O26.4, a similar site close to the channel centre is observed, but on hydration of this particular sample, the interstitial site is shown to be significantly displaced away from the channel centre towards the SiO4 units. This can be explained by the need for additional displacement from the channel centre to accommodate the large amount of interstitial anions in this hydrated phase. The solid state Si-29 MAS NMR spectra are shown to be very sensitive to the different speciation exhibited by the La8Sr2Si6O26 and La9.6Si6O26.4 systems, with the former being dominated by regular SiO4 framework species and the latter being dominated by interruptions to this network caused by cation vacancies and interstitials. The corresponding O-17 MAS NMR study identifies a strong signal from the O atoms of the SiO4 groups, thus demonstrating that all of the O species in these systems are exchangeable O under heterogeneous gas phase conditions. In addition, interstitial O species attributed to pendant OH linkages on the Si positions are clearly identified and resolved, and these are removed on dehydration. This observation and assignment is corroborated by corresponding H-1 MAS NMR measurements. Overall the neutron diffraction work indicates that the interstitial site location in these apatite silicates depends on the anion content with progressive displacement towards the SiO4 tetrahedra on increasing anion content, while the observation of exchangeable O on the SiO4 groups is consistent with prior modelling predictions as to the importance on the silicate units in the conduction process.
机译：磷灰石硅酸盐作为潜在的SOFC电解质材料引起了人们的极大兴趣。它们是非常规的氧化物离子导体，从某种意义上说，氧化物离子间隙（而不是空位）是关键缺陷。在这项工作中，我们比较了水合之前和之后的La9.6Si6O26.4和La8Sr2Si6O26的结构，以收集有关间隙氧化物离子位点位置的信息。中子衍射结构研究表明，在制备的La8Sr2Si6O26和水合La8Sr2Si6O26中，组织间氧化物离子位点靠近磷灰石通道中心。对于La9.6Si6O26.4，观察到接近通道中心的类似位点，但是在水合该特定样品时，间隙位置显示出显着地从通道中心移向SiO4单元。这可以解释为需要从通道中心移开以在该水合相中容纳大量间隙阴离子。固态Si-29 MAS NMR光谱显示对La8Sr2Si6O26和La9.6Si6O26.4系统表现出的不同形态非常敏感，前者以规则的SiO4骨架物质为主导，而后者则受到干扰。网络由阳离子空位和间隙引起。相应的O-17 MAS NMR研究确定了来自SiO4基团的O原子的强信号，因此证明了这些系统中的所有O物种在异相气相条件下都是可交换的O。此外，可以清楚地识别和分辨归因于Si位置OH侧链的间隙O物种，并在脱水时将其除去。相应的H-1 MAS NMR测量结果证实了这一观察和分配。总体而言，中子衍射工作表明，这些磷灰石硅酸盐中的间隙位置取决于阴离子含量，随着阴离子含量的增加，向SiO4四面体的位移逐渐增加，而观察到的SiO4基团上可交换的O与先前的模型预测一致在传导过程中硅酸盐单元的重要性。

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