Neutron Diffraction Study of Ba6Mn4MO15 (M = Cu, Zn): Long-Range Magnetic Order in Pseudo-1D Materials

Synthesis, Characterization, and Magnetic Properties of Uranium-Containing 2H-Perovskite-Related Sulfides: Ba3MUS6 (M = Mn, Fe, Co, Ni) and Ba3Co0.858(5)Mg0.142(5)US6

The uranium-containing 2H-perovskite-related chalcogenide family of compounds was revisited using the recently developed boron-chalcogen mixture (BCM) method for actinides to aid in their syntheses and to obtain magnetic measurements. Two known 2H-perovskite-related structures, Ba3MnUS6 and Ba3FeUS6, were synthesized using the BCM method and were found to exhibit antiferromagnetic transitions at TN = ∼7.6 and 10.8 K, respectively. Combining the BCM method with the molten flux crystal growth technique resulted in single crystals of three new compositions, Ba3NiUS6, Ba3CoUS6, and Ba3Co0.858(5)Mg0.142(5)US6, the synthesis and characterization of which is reported. Magnetic measurements of Ba3NiUS6 revealed a complex magnetic susceptibility consisting of a weak, glassy, antiferromagnetic transition near 65 K followed by an antiferromagnetic transition at TN = ∼18 K. A reduced radius ratio plot for the existing chalcogenide compositions and new additions to this structure type reported herein is presented to aid in the search for additional 2H-perovskite-related sulfides.

New Barium Cobaltite Series Ban+1ConO3n+3(Co8O8): Intergrowth Structure Containing Perovskite and CdI2-Type Layers

Single crystals of two new cobaltites, Ba2Co9O14 and Ba3Co10O17, were obtained from the flux of K2CO3 in the temperature range 800-890 degrees C. They crystallize in an intergrowth structure containing perovskite block and CdI2-type layers and can be attributed to the n = 1 and 2 members in a new intergrowth series of cobaltites, Ba(n+1)Co(n)O(3n+3)(Co8O8). Both Ba2Co9O14 and Ba3Co10O17 are metastable and transform into the known 2H-perovskite-related oxides at high temperature.

Time-Resolved in Situ Studies of Oxygen Intercalation into SrCoO2.5, Performed by Neutron Diffraction and X-ray Absorption Spectroscopy

Electrochemical oxidation of the antiferromagnetically ordered SrCoO(2.5), with brownmillerite-type structure, to the cubic ferromagnet SrCoO(3), with perovskite structure, has been investigated in situ by neutron diffraction as well as by X-ray absorption fine structure (XAFS) spectroscopy in specially designed electrochemical cells. The neutron diffraction experiments were performed twice, using two different wavelengths (lambda = 1.2921(2) and 4.74 A) in order to better discriminate structural and magnetic changes as functions of the charge transfer. From the neutron diffraction experiments, two intermediate phases, SrCoO(2.75) and SrCoO(2.82)(+/-)(0.07), were characterized. No superstructure reflections were observed for the corresponding SrCoO(2.75) phase. Instead we observed here, for the first time, 3D oxygen ordering during an oxygen intercalation reaction, as established for SrCoO(2.82)(+/-)(0.07), which can be described as a tetragonal unit cell, related to the perovskite cell by a approximately 2(a radical2) and c approximately 2a. The structure of this intermediate phase confirms the strongly topotactic character of the oxygen intercalation reaction. We were also able to prove, from in situ XAFS spectroscopy at the Co absorption edge, that the evolution of the Co valence state from formally +3 for SrCoO(2.5) to +4 for the final reaction product (SrCoO(3.0)) does not proceed continuously but gives evidence for the formation of O(-) species for stoichiometries corresponding to SrCoO(2.82)(+/-)(0.07). The use of neutrons (vs X-rays) in the diffraction experiments and the choice of the transmission (vs fluorescence) mode in the XAFS experiment guarantee that the obtained data well represent bulk and not just surface properties.

Structural and Magnetic Properties of Hexagonal Perovskites La1.2Sr2.7MO7.33 (M = Ru, Ir) Containing Peroxide Ions

The structures of the new compound La(1.2)Sr(2.7)IrO(7.33) and the recently discovered La(1.2)Sr(2.7)RuO(7.33) have been solved using a combination of X-ray and neutron diffraction. Both compounds crystallize in the trigonal space group Rm and consist of isolated MO6 (M = Ru, Ir) octahedra, which are arranged in well-defined hexagonal perovskite slabs. These slabs are separated by (Sr2O(1+delta)) layers containing both O2- and (O2)2- ions. The composition can therefore be written as La(1.2)Sr(2.7)MO(7-delta)(O2)delta with delta = 0.33. Results of the magnetic susceptibility and XANES measurements show that the transition metal cations are in a pentavalent state. While in La(1.2)Sr(2.7)RuO(7.33) an antiferromagnetic interaction between the Ru5+ ions is found, La(1.2)Sr(2.7)IrO(7.33) shows a very small temperature-independent paramagnetism down to 1.8 K due to the strong spin-orbit coupling characteristic for the 5d element iridium.

Growth of Sr6Rh5O15 single crystals from high-temperature solutions: structure determination using the traditional 3-D and the 4-D superspace group methods and magnetic measurements on oriented single crystals

Single crystals of Sr6Rh5O15 were grown from a molten potassium carbonate flux. The structure was solved by both the traditional 3-D crystallographic approach and the 4-D superspace group approach using JANA2000. Both methods produced an equivalent structure determination, thereby confirming the 4-D superspace group approach as an effective structure solution method for 3-D commensurate composite structures. Sr6Rh5O15 corresponds to the n = 1, m = 1 member of the A3n+3mA'nB3m+nO9m+6n family of 2H hexagonal perovskite-related oxides. This compound is characterized by pseudo-one-dimensional polyhedral chains of four face-sharing RhO6 octahedra followed by one RhO6 trigonal prism. These chains in turn are separated by [Sr](infinity) chains. Magnetic measurements were carried out on oriented single crystals, and a very large magnetic anisotropy in the magnetic susceptibility was observed.