Study of the Structural, Magnetic, and Electrical Properties of the 5H Hexagonal-Type Perovskite BaMn0.2Co0.8O2.80.

A combination of X-ray, neutron and electron diffraction, and high-resolution electron microscopy have been used to establish the 5H structural type of a new hexagonal-type perovskite BaMn0.2Co0.8O2.80. The structure can be described as a (cc′chh) 5H hexagonal polytype with ordered oxygen vacancies where the cubic c′ layer corresponds to a composition of [BaO2] as opposed to [BaO3]. The resulting layer structure consists of [MnCo2O12] blocks of three sharing faces octahedra linked by corners to two unconnected [CoO4] tetrahedra. Electron Energy Switch order Loss Spectroscopy shows Mn to be present only as Mn(+IV) and therefore Co is present as mixed +III/+IV. Mn(+IV) and Co(+III) ions are distributed over the face sharing octahedral sites whereas Co(+IV) ions are located on the tetrahedral sites. The magnetic behavior is more complex than is observed for BaCoO2.80 (a ferromagnet with Tc = 47 K) and can be described by a Stoner–Wohlfarth model of random-anisotropic, noninteracting monodomain ferromagnetic ...