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Author: Wolter, Anja U.B. × DDC: 540 ×

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    Laser-Assisted Floating Zone Growth of BaFe2S3 Large-Sized Ferromagnetic-Impurity-Free Single Crystals
    (Basel : MDPI, 2021) Amigó, Maria Lourdes; Maljuk, Andrey; Manna, Kaustuv; Stahl, Quirin; Felser, Claudia; Hess, Christian; Wolter, Anja U.B.; Geck, Jochen; Seiro, Silvia; Büchner, Bernd
    The quasi-one-dimensional antiferromagnetic insulator BaFe2S3 becomes superconducting under a hydrostatic pressure of ∼10 GPa. Single crystals of this compound are usually obtained by melting and further slow cooling of BaS or Ba, Fe, and S, and are small and needle-shaped (few mm long and 50–200 μm wide). A notable sample dependence on the antiferromagnetic transition temperature, transport behavior, and presence of superconductivity has been reported. In this work, we introduce a novel approach for the growth of high-quality single crystals of BaFe2S3 based on a laser-assisted floating zone method that yields large samples free of ferromagnetic impurities. We present the characterization of these crystals and the comparison with samples obtained using the procedure reported in the literature.
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    Layered manganese bismuth tellurides with GeBi4Te7- and GeBi6Te10-type structures: Towards multifunctional materials
    (London : RSC Publ., 2019) Souchay, Daniel; Nentwig, Markus; Günther, Daniel; Keilholz, Simon; de Boor, Johannes; Zeugner, Alexander; Isaeva, Anna; Ruck, Michael; Wolter, Anja U.B.; Büchnerde, Bernd; Oeckler, Oliver
    The crystal structures of new layered manganese bismuth tellurides with the compositions Mn0.85(3)Bi4.10(2)Te7 and Mn0.73(4)Bi6.18(2)Te10 were determined by single-crystal X-ray diffraction, including the use of microfocused synchrotron radiation. These analyses reveal that the layered structures deviate from the idealized stoichiometry of the 12P-GeBi4Te7 (space group P3m1) and 51R-GeBi6Te10 (space group R3m) structure types they adopt. Modified compositions Mn1-xBi4+2x/3Te7 (x = 0.15-0.2) and Mn1-xBi6+2x/3Te10 (x = 0.19-0.26) assume cation vacancies and lead to homogenous bulk samples as confirmed by Rietveld refinements. Electron diffraction patterns exhibit no diffuse streaks that would indicate stacking disorder. The alternating quintuple-layer [M2Te3] and septuple-layer [M3Te4] slabs (M = mixed occupied by Bi and Mn) with 1 : 1 sequence (12P stacking) in Mn0.85Bi4.10Te7 and 2 : 1 sequence (51R stacking) in Mn0.81Bi6.13Te10 were also observed in HRTEM images. Temperature-dependent powder diffraction and differential scanning calorimetry show that the compounds are high-temperature phases, which are metastable at ambient temperature. Magnetization measurements are in accordance with a MnII oxidation state and point at predominantly ferromagnetic coupling in both compounds. The thermoelectric figures of merit of n-type conducting Mn0.85Bi4.10Te7 and Mn0.81Bi6.13Te10 reach zT = 0.25 at 375 °C and zT = 0.28 at 325 °C, respectively. Although the compounds are metastable, compact ingots exhibit still up to 80% of the main phases after thermoelectric measurements up to 400 °C. © The Royal Society of Chemistry 2019.