Resolving the crystal-structural enigmas in Na-Super Ionic Conductors (NaSICON) of type A3M2(PO4)3, based on the A = Na, Li and M = Cr, Sc,

High ionic mobility in promising solid-state electrolytes of the NaSICON – type family depend of the temperature dependent distribution of alkaline ions over different crystallographic positions within the 3-dimensionally connected channel structure of the material. Ordering phenomena towards low temperature stepwise reduce the symmetry from the highly conduction, rhombohedral R-3c aristo structure towards monoclinic structures (C2/c, Cc, P21/c, P21/n), yet most of the intermediate states are unsolved and transition phenomena not fully understood. Using a combination of in-situ single – crystal and powder X-ray diffraction measurements (200 K <= T <= 600 K), the structural phase transition sequences will be studied on 4 representative compositions. From the obtained data we will be able to develop a general model for structural phase traditions in the NaSICON family of compounds having high potential in modern energy related material science.

在极具应用前景的NaSICON型（NaSICON-type）固体电解质家族中，高离子迁移率取决于碱金属离子在材料三维连通通道结构内不同晶体学位置上的温度依赖性分布。随着温度降低，有序化现象会逐步降低体系对称性：从高导电的菱面体R-3c原型（aristo）结构，逐步转变为单斜晶系结构（包括C2/c、Cc、P21/c、P21/n空间群），但目前多数中间态仍未被解析，相变机制也尚未完全阐明。本研究将采用原位单晶X射线衍射（in-situ single-crystal X-ray diffraction）与粉末X射线衍射（powder X-ray diffraction）联用的测试手段，测试温度范围为200 K ≤ T ≤ 600 K，针对4种代表性组分开展结构相变序列的研究。基于所获实验数据，我们将构建适用于NaSICON型化合物家族的通用结构相变模型，该类化合物在现代能源材料科学领域具有极高应用潜力。