Preparation and properties of Sr(CrMnFeCoNi)3O4 and Sr(MgAlTiCrFe)12O19 high entropy strontium ferrite systems and valance state analysis

Abstract

Two high-entropy ferrite ceramic systems, Sr(CrMnFeCoNi)12O19 and Sr(MgAlTiCrFe)12O19, were designed according to AB12O19 composition and synthesised using elevated-temperature solid phase reaction. The B-site was loaded with five atoms in equal proportions. We focused on preparing high-entropy hexagonal magnetoplumbite strontium ferrites. However, spinel structure significantly formed in the Sr(CrMnFeCoNi)12O19 system. The extruded strontium outside the lattice pulled out a part of chromium, causing phase separation and element segregation. The strontium extrusion outside the lattice and non-formation of hexagonal ferrite, which was reported for the first time, could be attributed to the electrovalence change in the elements. First-principles calculation of the (CrMnFeCoNi)3O4 spinel system was used to analyse the band structure and density state. After entropy engineering design, it was mutated into a wide direct band gap (2.3 eV at 0 K). Although the non-magnetic elements reduced the magnetic performance, they significantly improved the mechanical performance with a flexural strength of 208.7 ± 0.9 MPa. These results may contribute to the element selection and preparation of high-entropy strontium ferrites.