High-entropy oxide phases with magnetoplumbite structure

Abstract

Abstract Sintering of oxides and carbonates at 1400 °C gives crystalline high-entropy single phase products with a BaFe12O19 (magnetoplumbite) structure containing 5 doping elements at high concentration level: Ba(Fe6Ti1·2Co1·2In1.2Ga1.2Cr1.2)O19. The complete list of explored substitutions includes K, Ca, Sr, Pb, La, Bi, Al, Ga, In, Ti, V, Cr, Mn, Co, and Ni. Loading to the batch more than 5 dopants or introduction of NiO, or V2O5 initiates formation of second phases like spinels or vanadates. Bi2O3 and K2O are too volatile at sintering temperature and were evaporated from the samples. Due to large ionic radius, the In3+ cation is likely to be incorporated not only on Fe3+ sites, but also on Ba2+ sites, that follow from resulting crystal composition. The smallest di-valent and tri-valent cations, Sr2+ and Al3+, are found to preferably concentrate together in the same magnetoplumbite phase crystals within one sample. According to elemental analysis of selected hexagonal crystals in the investigated 8 doped samples the most prospective compositions for obtaining high-entropy single phase with magnetoplumbite structure can be formulated as (Ca,Sr,Ba,Pb,La)Fex(Al,Ga,In,Ti,Cr,Mn,Co)12-xO19 where x = 1.5–6.