Facile synthesis, characterization, and mechanical properties of spinel-structured high-entropy oxides: Lattice distortion and sluggish diffusion effects induced by aluminum cation

For the first time, we adopted the in-situ formed alumina , which resulted from the thermal decomposition of cheap and accessible potassium alum, as the source of aluminum cation to synthesize (Co 1/6 Mn 1/6 Fe 1/6 Cr 1/6 Ni 1/6 Al 1/6 ) 3 O 4 spinel-structured high-entropy oxide powder after the solid state reaction process, showing the advantages of lower synthesis temperature and scalable fabrication. To investigate the effect of aluminum cation insertion on the mechanical properties of (Co 1/6 Mn 1/6 Fe 1/6 Cr 1/6 Ni 1/6 Al 1/6 ) 3 O 4 , the (Co 1/6 Mn 1/6 Fe 1/6 Cr 1/6 Ni 1/6 Al 1/6 ) 3 O 4 and (Co 1/5 Mn 1/5 Fe 1/5 Cr 1/5 Ni 1/5 ) 3 O 4 ceramics were first fabricated and reported. Owing to significant lattice distortion induced by the aluminum cation, the (Co 1/6 Mn 1/6 Fe 1/6 Cr 1/6 Ni 1/6 Al 1/6 ) 3 O 4 possessed higher compressive strength , hardness, and elastic modulus , which were 139.3 MPa, 11.3 GPa, and 167.5 GPa, respectively. Moreover, the average grain size of (Co 1/6 Mn 1/6 Fe 1/6 Cr 1/6 Ni 1/6 Al 1/6 ) 3 O 4 only increased from 2.63 µm to 10.11 µm, while that of (Co 1/5 Mn 1/5 Fe 1/5 Cr 1/5 Ni 1/5 ) 3 O 4 increased from 1.77 µm to 15.61 µm. The slower grain growth rate of (Co 1/6 Mn 1/6 Fe 1/6 Cr 1/6 Ni 1/6 Al 1/6 ) 3 O 4 after aluminum cation insertion was attributed to the sluggish diffusion effect.