Glass-to-crystal transition of sodium(Na) super ionic conductors (NASICON)

利用全散射和布拉格衍射技术研究了钠超离子导体（NASICON）的玻璃-晶体转变。本文将研究两个取代序列：Na_(1+x)Al_xGe_(2-x)P_3O_12和Na_(1+x)Ti_2P_(3-x)Si_xO_12 （x = 0 ~ 2）。这些材料作为固体电解质或电极材料在钠基电池中被讨论作为锂基电池的替代品。NASICON材料得益于玻璃陶瓷合成的制备。然而，很少对玻璃结构进行研究。晶体结构只对烧结材料进行了研究。因此，微晶玻璃在结构上也没有很好地表征。无定形残留物不能确定，但会导致结晶相的成分变化。提出的工作旨在首次通过散射技术确定nasicon -玻璃的原子结构。玻璃相在不同长度尺度上的结构顺序可以通过往复空间数据，即第一个尖锐衍射峰的行为来确定。从散射数据的傅里叶变换得到的对分布函数（实空间）中提取键长和配位数。三维原子模型将通过反蒙特卡罗方法精炼为实验数据。额外的约束条件，如配位数，将由补充实验提供，如固态核磁共振。这将导致对原子结构的详细了解，这是解释离子键强度和离子迁移率的先决条件。陶瓷产品将通过Rietveld技术对结晶相和非晶残留物的精确组成进行表征。重新确定晶体结构，特别是关于取代和配位环境，将为玻璃相的结构工作提供参考点。这些材料呈均匀形核。在非硅质体系中，这种机理尚未得到研究。在结晶阈值处对不同退火样品的总散射方法将为玻璃在成核过程中的结构重组提供见解。了解局部环境从玻璃到结晶状态的变化将有助于指导新型快速离子导电玻璃和陶瓷的开发。此外，实验数据将有助于开发和验证预测模型，这些模型仍然不适合非晶体材料。最后，进行了高温全散射实验，对结晶过程进行原位监测。基于同步加速器的快速采集PDF （RAPDF）是研究玻璃相变化以及结晶相形成和组成的首选方法。这将使我们对微晶玻璃的形成有一个全面的了解。

The glass-to-crystal transition of sodium (Na) super ionic conductors (NASICON) will be investigated by total scattering and Bragg-diffraction techniques. Two substitution series will be studied: Na_(1+x)Al_xGe_(2-x)P_3O_12 and Na_(1+x)Ti_2P_(3-x)Si_xO_12 (x = 0 to 2). These materials are relevant as solid-electrolytes or as electrode materials in sodium-based batteries which are discussed as a replacement for lithium-based ones. NASICON materials benefit strongly from a preparation by a glass-ceramic synthesis. Nevertheless, the glass structures are hardly investigated. Crystal structures were only studied for sintered materials. Thus, the glass-ceramics are structurally not well characterized as well. Amorphous residues are not determined but will lead to compositional changes in the crystalline phases. The proposed work aims to determine the atomic structure of NASICON-glasses by scattering techniques for the first time. Structural ordering on different length scales of the glass phases can be determined from reciprocal-space data, i.e., from the behavior of the first sharp diffraction peak. Bond lengths and coordination numbers will be extracted from the pair-distribution function (real-space) obtained by Fourier transformation of the scattering data. 3-D atomic models will be refined to experimental data by the reverse Monte-Carlo method. Additional constraints, e.g., on coordination numbers, will be provided by complementary experiments, e.g. solid-state NMR. This will lead to detailed knowledge of the atomic structure which is a prerequisite to interpret the strength of ionic bonding and, therefore, ionic mobility. The ceramic products will be characterized regarding exact compositions of the crystalline phases and amorphous residues by the Rietveld technique. A Re-determination of crystal structures, especially regarding substitutions and coordination environments, will provide a reference point for the structural work on the glass phases. These materials show a homogeneous nucleation. Such a mechanism in was not investigated for non-siliceous systems, yet. A total scattering approach on differently annealed samples at the threshold of crystallization will provide insights into structural reorganization of the glasses during the nucleation process. The understanding of changes of the local environments from glass to crystalline state will help to guide the development of new fast ion-conducting glasses and ceramics. Furthermore, experimental data will help to develop and validate predictive models that are still inadequate for non-crystalline materials. Finally, a high temperature total scattering experiment will be done to monitor crystallization in situ. Synchrotron based rapid acquisition PDF (RAPDF) is the method of choice to study changes in the glassy phase as well as the formation and composition of crystalline phases. This will give us a comprehensive understanding of the formation of the glass-ceramics.