The new extremely substituted high entropy (Ba,Sr,Ca,La)Fe6-x(Al,Ti,Cr,Ga,In,Cu,W)xO19 microcrystals with magnetoplumbite structure

Abstract The high entropy oxide phase formation was investigated during solid state sintering at 1300–1350 °C in the BaO–SrO–CaO–La2O3–Fe2O3–Al2O3–TiO2–Cr2O3–Ga2O3–In2O3–CuO and BaO–SrO–CaO–La2O3–Fe2O3–Al2O3–Cr2O3–CoO-Ga2O3–In2O3-WO3 systems. The BaO–Fe2O3–Al2O3–TiO2–Cr2O3–Ga2O3–In2O3–CuO system was proved to form the single phase material with magnetoplumbite structure, which composition was represented by the formula Ba1.00Fe5.83Al1.19Ti1.08Cr1.12Cu0.78Ga1.03In0.97O19. Large configurational entropy of mixing of that phase resulted in significant incorporation of copper, known for its low solubility in the ternary Ba(Fe12-xCux)O19 phase. The structure parameters and magnetic properties of the single phase material were investigated. The Curie temperature of it was as low as 180.4 K due to dilution of high magnetic moment cations with zero magnetic moment cations. Nevertheless, the high concentration of high spin cations ensured enhanced paramagnetic properties of the material. In contrast to the first system, the BaO–SrO–CaO–La2O3–Fe2O3–Al2O3–Cr2O3–CoO-Ga2O3–In2O3-WO3 system formed two phases: the multicomponent spinel phase with low barium, strontium, calcium, lanthanum, and tungsten content along with the multicomponent (Ba, Sr, Ca, La) tungstate phase. High Gibbs energy of formation of the latter phase was the main obstacle for the high entropy magnetoplumbite phase formation.