Study of the Structural, Electronic, and Magnetic Properties of the Barium-Rich Iron(IV) Oxides, Ba₂FeO₄ and Ba₃FeO₅

Crystals of Ba2FeO4 and Ba3FeO5, grown from a “self-sealing” KOH−Ba(OH)2 flux, have been characterized by single-crystal X-ray diffraction, Mössbauer spectroscopy, and magnetic measurements. Ba2FeO4 forms nonmerohedral twinned crystals with the monoclinic space group P21/n, a = 6.034(2) Å, b = 7.647(2) Å, c = 10.162(3) Å, β = 92.931(6)°, and Z = 4. Ba3FeO5 crystallizes in the orthorhombic space group Pnma, with a = 10.301(1) Å, b = 8.151(1) Å, c = 7.611(1) Å, and Z = 4. While both compounds feature discrete FeO44- tetrahedra, the anion found in Ba2FeO4 has shorter Fe−O bonds and is significantly distorted relative to the Ba3FeO5 anion. An iron valence of 4+ was confirmed by magnet susceptibility measurements and by the low-temperature isomer shifts of −0.152 and −0.142 mm/s relative to α-iron for Ba2FeO4 and Ba3FeO5, respectively.