Cooperative mechanisms of fast-ion conduction in gallium-based oxides with tetrahedral moieties
Cooperative mechanisms of fast-ion conduction in gallium-based oxides with tetrahedral moieties
复制标题
DOI：
10.1038/nmat2039
复制
发表时间：
2007-11-01
期刊：
影响因子：
41.2
通讯作者：
Slater, Peter R.
中科院分区：
文献类型：
--
作者：
Kendrick, Emma;Kendrick, John;Slater, Peter R.
对更高能源效率的需求已获得越来越多的支持，以使用燃料电池技术，一个典型的例子是固体氧化物燃料电池(1,2)。此类设备的一个关键要求是良好的离子（O2- 或 H+）导体作为电解质 (3,4)。传统上，萤石型和钙钛矿型氧化物一直是目标(3-6)，尽管人们对中温（400-700 摄氏度）固体氧化物燃料电池的替代结构类型越来越感兴趣。特别是含有四面体部分的结构，例如La1-xCaxMO4-x/2(M= Ta, Nb, P)（参考文献7,8）、La1-xBa1+xGaO4-x/2（参考文献9,10）和La9.33+xSi6O26+3x/2（参考文献11），最近引起了相当大的关注。然而，仍然缺乏对这些系统中传导机制的原子尺度的理解；这种机制细节对于制定优化电导率的策略以及识别下一代材料非常重要。在此背景下，我们报告了 La1-xBa1+xGaO4-x/2 系统的综合实验和计算建模研究，该系统同时表现出质子和氧化物离子传导 (9,10)。在这里，我们表明，氧化物离子传导是通过协作的“齿轮”型过程进行的，涉及Ga2O7单元的断裂和重组，而质子传导的限速步骤是四面体内质子转移。这两种机制对于陶瓷氧化物材料来说都是不寻常的，并且类似的协同过程在包含四面体部分的相关系统中可能很重要。
The need for greater energy efficiency has garnered increasing support for the use of fuel-cell technology, a prime example being the solid-oxide fuel cell(1,2). A crucial requirement for such devices is a good ionic (O2- or H+) conductor as the electrolyte(3,4). Traditionally, fluorite- and perovskite-type oxides have been targeted(3-6), although there is growing interest in alternative structure types for intermediate-temperature (400-700 degrees C) solid-oxide fuel cells. In particular, structures containing tetrahedral moieties, such as La1-xCaxMO4-x/2(M= Ta, Nb, P) (refs 7,8), La1-xBa1+xGaO4-x/2 (refs 9,10) and La9.33+xSi6O26+3x/2 (ref. 11), have been attracting considerable attention recently. However, an atomic-scale understanding of the conduction mechanisms in these systems is still lacking; such mechanistic detail is important for developing strategies for optimizing the conductivity, as well as identifying next-generation materials. In this context, we report a combined experimental and computational modelling study of the La1-xBa1+xGaO4-x/2 system, which exhibits both proton and oxide-ion conduction(9,10). Here we show that oxide-ion conduction proceeds via a cooperative 'cog-wheel'-type process involving the breaking and re-forming of Ga2O7 units, whereas the rate-limiting step for proton conduction is intra-tetrahedron proton transfer. Both mechanisms are unusual for ceramic oxide materials, and similar cooperative processes may be important in related systems containing tetrahedral moieties.