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

Abstract

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 (Co1/6Mn1/6Fe1/6Cr1/6Ni1/6Al1/6)3O4 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 (Co1/6Mn1/6Fe1/6Cr1/6Ni1/6Al1/6)3O4, the (Co1/6Mn1/6Fe1/6Cr1/6Ni1/6Al1/6)3O4 and (Co1/5Mn1/5Fe1/5Cr1/5Ni1/5)3O4 ceramics were first fabricated and reported. Owing to significant lattice distortion induced by the aluminum cation, the (Co1/6Mn1/6Fe1/6Cr1/6Ni1/6Al1/6)3O4 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 (Co1/6Mn1/6Fe1/6Cr1/6Ni1/6Al1/6)3O4 only increased from 2.63 µm to 10.11 µm, while that of (Co1/5Mn1/5Fe1/5Cr1/5Ni1/5)3O4 increased from 1.77 µm to 15.61 µm. The slower grain growth rate of (Co1/6Mn1/6Fe1/6Cr1/6Ni1/6Al1/6)3O4 after aluminum cation insertion was attributed to the sluggish diffusion effect.