Masson Olivier, Berghout Abid, Béchade Emilie, Jouin Jenny, Thomas Philippe, Asaka Toru, Fukuda Koichiro
Science des Procédés Céramiques et de Traitements de Surface (SPCTS), CNRS, Centre Européen de la Céramique, Limoges Cedex, France.
Department of Environmental and Materials Engineering, Nagoya Institute of Technology, Nagoya, Japan.
Sci Technol Adv Mater. 2017 Sep 4;18(1):644-653. doi: 10.1080/14686996.2017.1362939. eCollection 2017.
The local structure of apatite-type lanthanum silicates of general formula La(SiO)O has been investigated by combining the atomic pair distribution function (PDF) method, conventional X-ray and neutron powder diffraction (NPD) data and density functional theory (DFT) calculations. DFT was used to build structure models with stable positions of excess oxide ions within the conduction channel. Two stable interstitial positions were obtained in accordance with literature, the first one located at the very periphery of the conduction channel, neighbouring the SiO tetrahedral units, and the second one closer to the channel axis. The corresponding PDFs and average structures were then calculated and tested against experimental PDFs obtained by X-ray total scattering and NPD Rietveld refinements results gathered from literature. It was shown that of the two stable interstitial positions obtained with DFT only the second one located within the channel is consistent with experimental data. This result consolidates one of the two main conduction mechanisms along the c-axis reported in the literature, namely the one involving cooperative movement of O4 and Oi ions.
通过结合原子对分布函数（PDF）方法、传统X射线和中子粉末衍射（NPD）数据以及密度泛函理论（DFT）计算，对通式为La(SiO)O的磷灰石型硅酸镧的局部结构进行了研究。DFT用于构建结构模型，其中过量的氧离子在传导通道内具有稳定位置。根据文献获得了两个稳定的间隙位置，第一个位于传导通道的最外围，与SiO四面体单元相邻，第二个更靠近通道轴。然后计算了相应的PDF和平均结构，并与通过X射线全散射获得的实验PDF以及从文献中收集的NPD Rietveld精修结果进行了对比测试。结果表明，通过DFT获得的两个稳定间隙位置中，只有位于通道内的第二个位置与实验数据一致。这一结果巩固了文献中报道的沿c轴的两种主要传导机制之一，即涉及O4和Oi离子协同移动的机制。
