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, Mossbauer spectroscopy, and magnetic measurements. Ba2FeO4 forms nonmerohedral twinned crystals with the monoclinic space group P2(1)/c, a = 6.034(2) Angstrom, b = 7.647(2) Angstrom, c = 10.162(3) Angstrom, beta = 92.931(6)degrees, and Z = 4. Ba3FeO5 crystallizes in the orthorhombic space group Pnma, with a = 10.301(1) Angstrom, b = 8.151(1) Angstrom, c = 7.611(1) Angstrom, 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 alpha-iron for Ba2FeO4 and Ba3FeO5, respectively.