A novel high entropy spinel-type aluminate MAl$_{2}$O$_{4}$(M = Zn, Mg, Cu, Co) and its lithiated oxyfluoride and oxychloride derivatives prepared by one-step mechanosynthesis

For the first time, a spinel-type high entropy oxide (Zn$_{0.25}$Cu$_{0.25}$Mg$_{0.25}$Co$_{0.25}$)Al$_{2}$O$_{4}$ as well as its derivative lithiated high entropy oxyfluoride Li$_{0.5}$(Zn$_{0.25}$Cu$_{0.25}$Mg$_{0.25}$Co$_{0.25}$)$_{0.5}$Al$_{2}$O$_{3.5}$F$_{0.5}$ and oxychloride Li$_{0.5}$(Zn$_{0.25}$Cu$_{0.25}$Mg$_{0.25}$Co$_{0.25}$)$_{0.5}$Al$_{2}$O$_{3.5}$Cl$_{0.5}$ are prepared in the nanostructured state via high-energy co-milling of the simple oxide precursors and the halides (LiF or LiCl) as sources of lithium, fluorine and chlorine. Their nanostructure is investigated by XRD, HR-TEM, EDX and XPS spectroscopy. It is revealed that incorporation of lithium into the structure of spinel oxide together with the anionic substitution has significant effect on its short-range order, size and morphology of crystallites as well as on its oxidation/reduction processes. The charge capacity of the as-prepared nanomaterials tested by cyclic voltammetry is found to be rather poor despite lithiation of the samples in comparison to previously reported spinel-type high entropy oxides. Nevertheless, the present work offers the alternative one-step mechanochemical route to novel classes of high entropy oxides as well as to lithiated oxyfluorides and oxychlorides with the possibility to vary their cationic and anionic elemental composition.