Department of Nuclear Engineering, University of Tennessee , Knoxville, Tennessee 37996, United States.
Department of Physics and Astronomy, University of Tennessee , Knoxville, Tennessee 37996, United States.
J Am Chem Soc. 2017 Aug 2;139(30):10395-10402. doi: 10.1021/jacs.7b04370. Epub 2017 Jul 21.
A wide variety of compositions adopt the isometric spinel structure (ABO), in which the atomic-scale ordering is conventionally described according to only three structural degrees of freedom. One, the inversion parameter, is traditionally defined as the degree of cation exchange between the A- and B-sites. This exchange, a measure of intrinsic disorder, is fundamental to understanding the variation in the physical properties of different spinel compositions. Based on neutron total scattering experiments, we have determined that the local structure of MgNiAlO spinel cannot be understood as simply being due to cation disorder. Rather, cation inversion creates a local tetragonal symmetry that extends over sub-nanometer domains. Consequently, the simple spinel structure is more complicated than previously thought, as more than three parameters are needed to fully describe the structure. This new insight provides a framework by which the behavior of spinel can be more accurately modeled under the extreme environments important for many geophysics and energy-related applications, including prediction of deep seismic activity and immobilization of nuclear waste in oxides.
多种成分采用等轴尖晶石结构 (ABO)，其中原子尺度的有序性通常仅根据三个结构自由度来描述。一个是反演参数，传统上定义为 A 位和 B 位之间的阳离子交换程度。这种交换是固有无序的一种度量，对于理解不同尖晶石成分的物理性质变化至关重要。基于中子总散射实验，我们已经确定 MgNiAlO 尖晶石的局部结构不能简单地归因于阳离子无序。相反，阳离子反演会产生局部四方对称性，这种对称性会延伸到亚纳米域。因此，简单的尖晶石结构比以前想象的要复杂，因为需要三个以上的参数才能完全描述结构。这种新的认识为尖晶石在许多地球物理和能源相关应用中重要的极端环境下的行为提供了一个更准确的建模框架，包括对深部地震活动的预测和氧化物中核废料的固定。
