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In the current work, a simple mechanochemical route has been employed to preparatively access three spinel‐type compositionally complex ceramics, i. e., (Co, Fe, Mn)₃O₄, (Co, Fe, Mn, Ni)₃O₄, and (Co, Cr, Fe, Mn, Ni)₃O₄. Hydrated nitrate salts of the respective transition metal elements were mechanically ground with ammonium hydrogen carbonate. The resulting paste‐like mixture of metal hydroxides, oxyhydroxides, and carbonates was rinsed with water to remove the byproduct (NH₄NO₃) and converted into the respective single‐phase spinel‐type oxides via calcination. In situ X‐ray diffraction (XRD) revealed the formation of the spinel‐type structure (Fd 3‾m) already at temperatures as low as 150 °C. Typically, the calcination of the precursors at temperatures beyond 500 °C led to the formation of well‐crystallized, single‐phase spinel‐type oxides with nearly equimolar composition and highly homogeneous distribution of the transition metals within the structure. The mechanochemical synthesis route in the present study is considered to be an easy, straightforward, and scalable access to compositionally complex oxides.

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