Browsing by Author "Maljuk, A"

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    A (3 + 3)-dimensional “hypercubic” oxide-ionic conductor: type ii bi2o3–nb2o5
    (ACS Publications, 2013-04-09) Ling, CD; Schmid, S; Blanchard, PER; Petříček, V; McIntyre, GJ; Sharma, N; Maljuk, A; Yaremchenko, AA; Kharton, VV; Gutmann, MJ; Withers, RL
    The high-temperature cubic form of bismuth oxide, δ-Bi2O3, is the best intermediate-temperature oxide-ionic conductor known. The most elegant way of stabilizing δ-Bi2O3 to room temperature, while preserving a large part of its conductivity, is by doping with higher valent transition metals to create wide solid-solutions fields with exceedingly rare and complex (3 + 3)-dimensional incommensurately modulated ?hypercubic? structures. These materials remain poorly understood because no such structure has ever been quantitatively solved and refined, due to both the complexity of the problem and a lack of adequate experimental data. We have addressed this by growing a large (centimeter scale) crystal using a novel refluxing floating-zone method, collecting high-quality single-crystal neutron diffraction data, and treating its structure together with X-ray diffraction data within the superspace symmetry formalism. The structure can be understood as an ?inflated? pyrochlore, in which corner-connected NbO6 octahedral chains move smoothly apart to accommodate the solid solution. While some oxide vacancies are ordered into these chains, the rest are distributed throughout a continuous three-dimensional network of wide δ-Bi2O3-like channels, explaining the high oxide-ionic conductivity compared to commensurately modulated phases in the same pseudobinary system. © 2013, American Chemical Society.
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    Competing exchange interactions on the verge of a metal-insulator transition in the two-dimensional spiral magnet Sr3Fe2O7
    (Americal Physical Society, 2014-10-03) Kim, JH; Jain, A; Reehuis, M; Khaliullin, G; Peets, DC; Ulrich, C; Park, JT; Faulhaber, E; Hoser, A; Walker, HC; Adroja, DT; Walters, AC; Inosov, DS; Maljuk, A; Keimer, B
    We report a neutron scattering study of the magnetic order and dynamics of the bilayer perovskite Sr 3 Fe 2 O 7 , which exhibits a temperature-driven metal-insulator transition at 340 K. We show that the Fe 4+ moments adopt incommensurate spiral order below T N =115  K and provide a comprehensive description of the corresponding spin-wave excitations. The observed magnetic order and excitation spectra can be well understood in terms of an effective spin Hamiltonian with interactions ranging up to third-nearest-neighbor pairs. The results indicate that the helical magnetism in Sr 3 Fe 2 O 7 results from competition between ferromagnetic double-exchange and antiferromagnetic superexchange interactions whose strengths become comparable near the metal-insulator transition. They thus confirm a decades-old theoretical prediction and provide a firm experimental basis for models of magnetic correlations in strongly correlated metals. © 2014, American Physical Society.
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    Growth of LiCoO2 single crystals by the TSFZ method
    (American Chemical Society, 2018-11-08) Nakamura, S; Maljuk, A; Maruyama, Y; Nagao, M; Watauchi, S; Hayashi, T; Anzai, Y; Furukawa, Y; Ling, CD; Deng, G; Avdeev, M; Büchner, B; Tanaka, I
    We have grown LiCoO2 single crystals by the traveling solvent floating zone (TSFZ) growth with Li-rich solvent, having observed the incongruent melting behavior of LiCoO2 between 1100 and 1300 °C. The optimum growth conditions in terms of atmosphere and solvent composition were determined to be Ar flow and an atomic ratio Li/Co 85:15, respectively. The crystals grown using a conventional-mirror-type furnace contained periodic inclusions of a Co–O phase due to the influence of Co–O phase segregation on the stability of the molten zone during growth. By using a tilted-mirror FZ furnace, inclusion-free LiCoO2 crystals of about 5 mm in diameter and 70 mm long were obtained at a tilting angle θ = 10°. The grown crystals were confirmed to be single-domain by neutron Laue diffraction. © 2018 American Chemical Society
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    Magnetic phase diagram of Sr3Fe2O7-delta
    (American Physical Society, 2013-06-10) Peets, DC; Kim, JH; Dosanjh, P; Reehuis, M; Maljuk, A; Aliouane, N; Ulrich, C; Keimer, B
    Magnetometry, electrical transport, and neutron scattering measurements were performed on single crystals of the Fe4+-containing perovskite-related phase Sr3Fe2O7−δ as a function of oxygen content. Although both the crystal structure and electron configuration of this compound are closely similar to those of well-studied ruthenates and manganates, it exhibits very different physical properties. The fully oxygenated compound (δ=0) exhibits a charge-disproportionation transition at TD=340 K, and an antiferromagnetic transition at TN=115 K. For temperatures T≤TD, the material is a small-gap insulator; the antiferromagnetic order is incommensurate, which implies competing exchange interactions between the Fe4+ moments. The fully deoxygenated compound (δ=1) is highly insulating, and its Fe3+ moments exhibit commensurate antiferromagnetic order below TN∼600 K. Compounds with intermediate δ exhibit different order with lower TN, likely as a consequence of frustrated exchange interactions between Fe3+ and Fe4+ sublattices. A previous proposal that the magnetic transition temperature reaches zero is not supported. © 2013, American Physical Society.
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    Neutron diffraction study of spin and charge ordering in SrFeO3-delta
    (American Physical Society, 2012-05-22) Reehuis, M; Ulrich, C; Maljuk, A; Niedermayer, C; Ouladdiaf, B; Hoser, A; Hofmann, T; Keimer, B
    We report a comprehensive neutron diffraction study of the crystal structure and magnetic order in a series of single-crystal and powder samples of SrFeO3-delta in the vacancy range 0 <= delta <= 0.23. The data provide detailed insights into the interplay between the oxygen vacancy order and the magnetic structure of this system. In particular, a crystallographic analysis of data on Sr8Fe8O23 revealed a structural transition between the high-temperature tetragonal and a low-temperature monoclinic phase with a critical temperature T = 75 K, which originates from charge ordering on the Fe sublattice and is associated with a metal-insulator transition. Our experiments also revealed a total of seven different magnetic structures of SrFeO3-delta in this range of delta, only two of which namely an incommensurate helix state in SrFeO3 and a commensurate, collinear antiferromagnetic state in Sr4Fe4O11) had been identified previously. We present a detailed refinement of some of the magnetic ordering patterns and discuss the relationship between the magnetotransport properties of SrFeO3-delta samples and their phase composition and magnetic microstructure. © 2012, American Physical Society.