title: An unusual high-spin ground state of Co3+ in octahedral coordination in brownmillerite-type cobalt oxide.
abstract: The crystal and magnetic structures of brownmillerite-like Sr(2)Co(1.2)Ga(0.8)O(5) with a stable Co(3+) oxidation state at both octahedral and tetrahedral sites are refined using neutron powder diffraction data collected at 2 K (S.G. Icmm, a = 5.6148(6) Å, b = 15.702(2) Å, c = 5.4543(6) Å; R(wp) = 0.0339, R(p) = 0.0443, χ(2) = 0.775). The very large tetragonal distortion of CoO(6) octahedra (1.9591(4) Å for Co-O(eq) and 2.257(6) Å for Co-O(ax)) could be beneficial for the stabilization of the long-sought intermediate-spin state of Co(3+) in perovskite-type oxides. However, the large magnetic moment of octahedral Co(3+) (3.82(7)μ(B)) indicates the conventional high-spin state of Co(3+) ions, which is further supported by the results of a combined theoretical and experimental soft X-ray absorption spectroscopy study at the Co-L(2,3) edges on Sr(2)Co(1.2)Ga(0.8)O(5). A high-spin ground state of Co(3+) in Sr(2)Co(1.2)Ga(0.8)O(5) resulted in much lower in comparison with a LaCoO(3) linear thermal expansion coefficient of 13.1 ppm K(-1) (298-1073 K) determined from high-temperature X-ray powder diffraction data collected in air.
authors: MSU-MPG Partner Group and the Chemistry Department, Lomonosov Moscow State University, Russia. istomin@icr.chem.msu.ru.
authors: S Ya
authors: SY
authors: Istomin
authors: O A
authors: OA
authors: Tyablikov
authors: S M
authors: SM
authors: Kazakov
authors: E V
authors: EV
authors: Antipov
authors: A I
authors: AI
authors: Kurbakov
authors: A A
authors: AA
authors: Tsirlin
authors: N
authors: N
authors: Hollmann
authors: Y Y
authors: YY
authors: Chin
authors: H-J
authors: HJ
authors: Lin
authors: C T
authors: CT
authors: Chen
authors: A
authors: A
authors: Tanaka
authors: L H
authors: LH
authors: Tjeng
authors: Z
authors: Z
authors: Hu