Coduri Mauro, Fracchia Martina, Checchia Stefano, Manzoli Maela, Dejoie Catherine, Ghigna Paolo, Anselmi-Tamburini Umberto
Chemistry Department, University of Pavia, via Taramelli 16, Pavia, 27100, Italy.
INSTM, National Inter-University Consortium for Materials Science and Technology, Via G. Giusti 9, Florence, 50121, Italy.
Small. 2025 Feb;21(5):e2406634. doi: 10.1002/smll.202406634. Epub 2024 Dec 19.
The temperature-resolved structure evolution of quinary and quaternary equimolar oxides containing Mg, Ni, Zn, Co, and Cu is investigated by in situ synchrotron diffraction. Important structural modifications occur already at mild temperatures and depend on the elements involved. All quaternary compounds with χ(Cu) = 0.25 within 250-500 °C show a tetragonal phase. The fraction of Cu dictates the degree of the tetragonal distortion: for χ(Cu) = 0.20 only local distortions are observed, which do not occur in the absence of Cu. Further heating restores the original cubic phase, followed by the segregation of other phases, which depend on the elements available. In the presence of both Cu and Mg, the segregation of guggenite is observed, a phase with a cation connectivity similar to the cubic high entropy oxide, but with a suitable coordination environment for Cu atoms by allowing strong elongation of octahedra. Guggenite acts as a buffer layer facilitating the gradual diffusion of Cu from the cubic high entropy oxide to tenorite. To conclude, it is demonstrated for the first time that the demixing of the prototypal high entropy oxide does not involve just tenorite or binary oxides, it is rather mediated by the formation of guggenite.
通过原位同步加速器衍射研究了含镁、镍、锌、钴和铜的五元及四元等摩尔氧化物的温度分辨结构演变。重要的结构变化在温和温度下就已出现，且取决于所涉及的元素。在250 - 500°C范围内，所有χ(Cu) = 0.25的四元化合物都呈现四方相。铜的含量决定了四方畸变的程度：对于χ(Cu) = 0.20，仅观察到局部畸变，在没有铜的情况下不会出现这种情况。进一步加热会恢复原始的立方相，随后会析出其他相，这取决于可用的元素。在同时存在铜和镁的情况下，观察到古根石的析出，这是一种阳离子连接性与立方高熵氧化物相似的相，但通过允许八面体强烈伸长为铜原子提供了合适的配位环境。古根石作为缓冲层，促进了铜从立方高熵氧化物向黑铜矿的逐渐扩散。总之，首次证明了典型高熵氧化物的分解不仅仅涉及黑铜矿或二元氧化物，而是由古根石的形成介导的。
