Npj Comput. Mater.:高熵化合物—氧空位的元素组成调控
单相多组分金属和陶瓷固溶体，由于其构型熵的作用而使这类材料的单相可稳定存在，而引起了广泛的关注。对于陶瓷材料来说，这些所谓的高熵或熵稳定相具有很大的构型熵，这种构型熵源于体系中一个或多个阳离子亚晶格的化学无序，而阴离子亚晶格(通常，但不一定)仍存在有序结构。从近期的发现来看，高熵氧化物已经表现出了卓越的电化学和电子功能特性，如高离子迁移率、高锂存储-循环稳定性、高效的高温热化学水分裂性、磁交换耦合性和巨大的介电性。而在这些高熵化合物中，空位缺陷则会影响材料的性能。例如，空位形成的传导路径会影响质子和Li+离子的扩散；氧空位也可以影响光电化学水分解过程中的光吸收和电荷分离；介电响应可以通过空位和缺陷复合产生受体、供体和阱态等多种状态。显然，理解和控制这些材料中缺陷的形成，对理解其功能特性至关重要。然而在具有大构型熵的氧化物中，大范围的化学无序如何影响缺陷的形成，至今不得而知。
Entropic stabilization has evolved into a strategy to create new oxide materials and realize novel functional properties engineered through the alloy composition. Achieving an atomistic understanding of these properties to enable their design, however, has been challenging due to the local compositional and structural disorder that underlies their fundamental structure-property relationships. Here, we combine high-throughput atomistic calculations and linear regression algorithms to investigate the role of local configurational and structural disorder on the thermodynamics of vacancy formation in (MgCoNiCuZn)O-based entropy-stabilized oxides (ESOs) and their influence on the electrical properties. We find that the cation-vacancy formation energies decrease with increasing local tensile strain caused by the deviation of the bond lengths in ESOs from the equilibrium bond length in the binary oxides. The oxygen-vacancy formation strongly depends on structural distortions associated with the local configuration of chemical species. Vacancies in ESOs exhibit deep thermodynamic transition levels that inhibit electrical conduction. By applying the charge-neutrality condition, we determine that the equilibrium concentrations of both oxygen and cation vacancies increase with increasing Cu mole fraction. Our results demonstrate that tuning the local chemistry and associated structural distortions by varying alloy composition acts an engineering principle that enables controlled defect formation in multi-component alloys.
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