具有新型层状共生结构的含镓氧化物的设计合成和离子导电性研究

The gallium-containing oxides is our target system because the flexible coordination modes of Ga3+ with 4, 5, or 6 oxygens is beneficial to the oxygen immigration at high temperature by losing or accepting oxygen atoms. Considering the similar layered type structures in stuffed tridymite- and CaGa4O7, we rationally design a series of possible intergrowth structures with the general formula (CaPbGa4O8)n(CaGa4O7)m. During the preliminary investigation, two members of CaPbGa4O8 and Ca2PbGa8O15 were indeed realized by solid state reactions and their structures were determined by powder X-ray and neutron diffraction. Note that Ca2PbGa8O15 is the first example of intergrowth compounds not based on the closed-packing-structures. This project is therefore proposed on the basis of these two new oxides. We plan to substitute with rare earth cations, Bi3+, Ge4+ to gain interstitial oxygen, or dope with alkaline metal, Zn2+ to obtain oxygen vacancies, followed by the examination of high temperature oxygen ionic conductivity. It is also necessary to study the location and the concentration of the oxygen vacancies or interstitial oxygen in the structure through the combination of neutron diffraction and inelastic scattering, to shed the light of the conducting mechanism. In addition, we also propose to facilitate the soft-chemistry synthetic methods to discover other new layered intergrowth oxides in this system or even other complex phase diagrams. In summary, rational design of new structures and solving them with powder diffraction techniques are both important characteristics of our project.

申请人研究含镓氧化物是因为镓可与氧形成4、5或6配位，在高温下镓氧多面体容易脱去或接受氧，实现氧离子传输。申请人选择具有相似层状结构的填充式鳞石英和CaGa4O7组合，设计(CaPbGa4O8)n(CaGa4O7)m共生型系列氧化物，在前期研究中已获得CaPbGa4O8与Ca2PbGa8O15，利用粉末X射线和中子衍射解析晶体结构，其中Ca2PbGa8O15是第一例非密堆积类型的层状共生结构。本项目将基于这两个新氧化物，利用高价金属离子如稀土、Bi3+、Ge4+或低价离子如碱金属、Zn2+等对Ca/Pb/Ga适量取代，在结构中引入间隙氧或氧空位，测试氧离子导电行为，并通过中子衍射或全散射手段研究缺陷状态，进而分析氧离子导电机制。此外，申请人将利用软化学合成等方法探索这个系列中其它可能存在的新型氧化物，并拓展至其他复合金属氧化物体系。本项目研究特色在于新结构设计以及利用粉末衍射解析未知结构。

镓离子可与氧形成柔性的4、5或6配位，不仅利于氧缺陷的稳定，还有助于氧离子在不同GaOn多面体（n = 4、5、6）之间传递，进而实现氧离子导电。我们希望通过探索合成新型含镓复合金属氧化物，并通过不等价离子掺杂来构造氧缺陷，以获得具有高离子电导率的氧离子导体材料。利用离子之间电荷、离子半径、化学性质的差异，我们设计合成了若干新型含镓复合金属氧化物，包括Ca2PbGa8O15，CaPbGa4O8, Ca1-xSrxGa2O4 (x = 0.2-0.95)，CaBa1-xPbxZn2Ga2O7，Ca7Mg2Ga6O18以及Sr11Zn12-δGa6O33-δ。运用粉末X射线衍射、同步辐射以及高分辨中子衍射从头解析了它们的晶体结构，并对他们的结构进行了系统分析与研究，揭示了它们的结构化学本质。例如，我们设计合成了第一例非密堆积型纯面体结构的层状共生氧化物Ca2PbGa8O15，其结构稳定与Pb2+的孤对电子效应及Ca/Pb离子有序密切相关。CaBa1-xPbxZn2Ga2O7的反常晶格扩张起源于Pb-O共价键协同晶格应力释放。此外，这些新型含镓氧化物都可以容纳一定的氧空位缺陷，但它们的三维骨架结构不利于氧离子长程迁来获得离子导电。通过本项目的研究，我们认识到具有低维柔性结构的含镓氧化物可能是潜在优异氧离子导体材料，这对定向设计合成高氧离子电导率的含镓复合金属氧化物具有重要的指导意义。