A study of the structure-composition-properties correlation is reported for the oxygen-deficient SrFeCoO (x = 0.1-0.85) materials. The introduction of Co in the parent SrFeO (SrFeO) structure revealed an interesting structural transformation. At room temperature (RT), an orthorhombic (space group Cmmm, 2√2a × 2a × √2a type, a = lattice parameter of the cubic perovskite) → tetragonal (space group P4/mmm, a × a × 2a type) → tetragonal (space group I4/mmm, 2a × 2a × 4a type) structural transformation is observed in parallel with increasing Co content and decreasing oxygen content in the structure. At the same time, a rich variation in the magnetic properties is explored. The samples with x = 0.25, 0.3 show temperature-induced magnetization reversal. With increasing Co content in the structure, magnetic interactions start to weaken due to the random distribution of Fe and Co in the structure; the x = 0.5 sample shows frustration in the magnetic behavior with much smaller magnetization value. With a further increase in the Co content in the structure, RT ferrimagnetic-type behavior is observed for the sample with x = 0.85. The nuclear and magnetic structure refinements using RT and low-temperature neutron powder diffraction (NPD, 10 K) patterns confirm the formation of a "314-type" novel oxygen vacancy ordered phase for the sample with x = 0.85, which is the first case of "314-type" novel oxygen vacancy ordering without A-site (ABO type perovskite) ordering. The magnetic structure is G-type antiferromagnetic starting at room temperature. Further, the stabilization of the "314-type" complex superstructure is related to the ordering of oxygen vacancies in the oxygen-deficient Co-O layers, and the same assists in building a network of Co ions with different coordination environments, each with different spin states, and forms the spin-state ordering.

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We describe the synthesis and the crystallographic and magnetic properties of a novel NaCoCr2(PO4)3 phosphate. A conventional solid-state reaction was used to obtain single-phase powders. A Rietveld analysis of powder X-ray diffraction data proposes an orthorhombic symmetry similar to α-CrPO4-type structure in space group Imma with the following unit cell parameters: a = 10.413(1) Å; b = 13.027(1) Å; c = 6.372(1) Å. The framework consists of PO4 tetrahedra, M(1)O6 (M(1) = Cr) octahedra, and M(2)2O10 (M(2) = 0.5Cr+0.5Co) binuclear unit of edge-sharing MO6 octahedra. It can be described in terms of two building blocks: sheets consisting of corner-sharing M(2)2O10 units with PO4 tetrahedra found parallel to the (b,c) plane, and chains made by corner-sharing CrO6 octahedra and PO4 tetrahedra running along the b axis. From the interconnection of the sheets and chains, a 3D rigid skeleton is formed, exhibiting two kinds of intersecting tunnel channels containing the Na(+) ions. The proposed structure derives from the α-CrPO4-type structure considering a positive charge balance according to the equation Cr(3+) → Co(2+) + Na(+), resulting in sodium countercation introduction within the unoccupied channels shown in the α-CrPO4 framework. Temperature-dependent DC and AC magnetic susceptibility is indicative of a long-range magnetic ordering occurring at 32 K. Further, spin-flop transition sheds light on a chromium-based phosphate for the first time.

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Abstract:There is ongoing effort to identify novel materials that have performance better than LiCoO 2 . The objective of this work is to explore materials in the system (1 -x -y) LiNi 0.8 Co 0.2 O 2 • xLi 2 MnO 3 • yLiCoO 2 . A ternary composition diagram was used to identify sample points, and compositions for testing were initially chosen. Detailed characterization of the synthesized materials was done, including Rietveld Refinement of XRD data, XPS analysis for valence state of transition-metals, SEM for microstructure details, and TGA for thermal stability of the materials. Electrochemical performance showed that discharge capacities on the order of 230 mAh/g were obtained. Preliminary results showed that these materials exhibit good cycling capabilities thereby positioning these materials as promising for Li-ion battery applications.

SrFeCoO was synthesized by a solid-state reaction. Its structural study at room temperature using conventional X-ray as well as neutron powder diffraction, electron diffraction and high-resolution transmission electron microscopy is presented. An oxygen-vacancy ordering related to the "314" model known for the SrYCoO oxide is proposed despite neither an A-site ordering nor an A-site mismatch. By means of Mössbauer spectroscopy, Mohr salt titration and the difference in the neutron cross sections of Fe and Co, a cation distribution within the crystallographic sites as the following Sr(FeCo)(FeCoCo)O is suggested, highlighting a natural layered structure with Fe and Co in higher oxidation states in the oxygen replete layers than in the oxygen deficient ones.

Transition. -The new title compound is prepared by solid state reaction of a stoichiometric mixture of Na 2CO3, Co(NO3)2, Cr(NO3)3, and (NH4)H2PO4 (Pt crucible, 1423 K, 48 h). NaCoCr2(PO4)3 is characterized by powder XRD, and magnetic and specific heat measurements. It crystallizes in the orthorhombic space group Imma with Z = 4. The framework consists of PO 4 tetrahedra, CrO6 octahedra, and (0.5Cr + 0.5Co)2O10 binuclear units of edge-sharing (0.5Cr + 0.5Co)O 6 octahedra. Na + ions are located within intersecting tunnels delimited by the framework. The compound shows a magnetic phase transition from para-to antiferromagnetic behavior at about 32 K. A spin-flop transition is likely due to the competition within the (0.5Cr + 0.5Co)2O10 bioctahedral units between Co 2+ -O(2p)-Cr 3+ ferromagnetic 90 superexchange interactions and Cr 3+ -O(2p)-Cr 3+ antiferromagnetic 90 superexchange interactions, and mediated by direct exchange. -(SOUIWA, K.; CHENNABASAPPA, M.; DECOURT, R.; BEN AMARA, M.; HIDOURI*, M.; TOULEMONDE, O.; Inorg. Chem. 54 (2015) 15, 7345-7352, http://dx.doi.org/10.1021/acs.inorgchem.5b00776 ; Fac. Sci., Univ. Monastir, 5019 Monastir, Tunisia; Eng.) -W. Pewestorf 41-012