高温高压下磷灰石型锗酸镧材料的结构与电学特性研究

Apatite-type lanthanum germanates (ATLG) as novel intermediate-temperature solid electrolytes have great application prospects. However, there are two key scientific issues that limit ATLG's development and application: 1) the influence law of ATLG's structural changes with temperature and pressure on the electrical properties is still unclear; 2) it is difficult to obtain highly densified ATLG without the loss of germanium. In this project, based on the comprehensive investigation and preliminary research, we plan to systematically study the basic laws, physical mechanisms and internal relations of the changes of ATLG's crystal structure and electrical properties with temperature and pressure using the diamond anvil cell in situ high-pressure experimental technology, deeply explore the changes of the key structural unit GeO4 tetrahedron with temperature and pressure and the physical essence of its influence on the ATLG's electrical properties, and obtain the temperature and pressure phase diagram of ATLG. On the basis of the above researches, we plan to capture the high-performance high-pressure metastable phase of ATLG using the cubic high-pressure apparatus high-temperature and high-pressure experimental technique, meanwhile solve the technical problem that the conventional methods can not achieve pure and highly densified ATLG, finally implement the controllable preparation of pure, highly dense and high-performance ATLG. The implementation of this project will not only can obtain the evolution laws and mechanisms of ATLG's crystal structure and electrical properties with temperature and pressure, but also can establish a new high-temperature and high-pressure optimization way of ATLG's physical properties, and which will provide a new research perspective and experimental basis for the optimization of ATLG's physical properties.

磷灰石型锗酸镧（ATLG）是一种极具应用前景的新型中温固态电解质材料。而目前限制其发展与应用的关键科学问题是：1)其结构随温压变化进而对电学特性的影响规律尚不清楚，2)难以在避免锗流失的前提下实现其高度致密化。本项目在综合调研和前期研究的基础上，提出拟利用金刚石对顶砧原位高温高压实验技术，系统研究ATLG结构与电学特性随温压变化的规律、机制及内在关联，深入探究关键结构单元GeO4四面体随温压变化进而影响电学特性的物理本质，获得ATLG的温压相图；并在此基础上，采用六面顶高温高压实验技术，探索“截获”性能更优的高压亚稳相ATLG，同时解决常规方法无法克服的“致密化与锗流失”矛盾难题，实现纯净、高度致密且性能更优的新型ATLG的可控制备。本项目的实施不仅可以获得ATLG物性随温压变化的规律与机制，还有望建立ATLG物性优化的高温高压新途径，并为ATLG的物性优化提供新的研究角度与实验依据。

磷灰石型锗酸镧（ATLG）是一种极具应用前景的新型中温固态电解质材料，决定着ATLG基固体氧化物燃料电池（SOFC）的能量转换效率和稳定性。但目前常规技术难以在避免锗流失的前提下实现ATLG材料的高度致密化，且ATLG材料的结构随温压变化进而对电学特性的影响规律与机制尚不清楚，极大限制了其发展与应用。本项目采用NaCl熔盐法制备优质ATLG粉体材料，继而利用金刚石对顶砧原位高压实验技术对其结构随压力变化的规律与机制进行系统研究，随后利用六面顶高温高压实验技术探索“截获”性能更优的高压亚稳相ATLG，同时解决常规方法无法克服的“致密化与锗流失”矛盾难题，实现纯净、高度致密且性能更优的新型ATLG的可控制备。研究表明，NaCl熔盐法在900℃/4h的烧结条件下，可获得尺寸均匀（~200nm）、无团聚、结晶性好的优质ATLG粉体；高压下ATLG材料会发生由P63/m对称性到P63对称性的微妙结构相变，相变过程伴随着明显的c轴轴向塌缩，其主要原因是压力造成GeO4四面体构成的多孔结构框架与内部结构单元之间的压力失衡，进而导致GeO4四面体的靠近、倾斜与旋转，并随压力的增加GeO4四面体的空间位置、形态及排列方式不断变化，最终诱发ATLG材料结构由高的P63/m对称性向低的P63对称性转变，进而为GeO4四面体旋转提供更大的自由度，因此高压亚稳相更容易被压缩且理论导电性更好；对优质ATLG粉体进行高温高压（900-1100℃/3.0-4.5GPa）优化成型后，ATLG片体材料的纯净度与致密度显著提升，其电导率较常规烧结样品提升了一个数量级以上。本项目的实施不仅获得了ATLG结构随压力变化的规律与机制，还建立ATLG物性优化的高温高压新途径，对推动ATLG的发展与应用具有重要的科学意义。