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961 results on '"Hoffmann, Rolf‐Dieter"'

201. Ferromagnetic Ordering in GdPdCd.

Author

Hoffmann, Rolf-Dieter, primary, Poettgen, Rainer, additional, Fickenscher, Thomas, additional, Felser, Claudia, additional, Latka, Kazimierz, additional, and Kmiec, Roman, additional

Published
2010
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209. Superconductivity in Quasi One‐Dimensional Carbides

Author

Scherer, Wolfgang, primary, Hauf, Christoph, additional, Presnitz, Manuel, additional, Scheidt, Ernst‐Wilhelm, additional, Eickerling, Georg, additional, Eyert, Volker, additional, Hoffmann, Rolf‐Dieter, additional, Rodewald, Ute C., additional, Hammerschmidt, Adrienne, additional, Vogt, Christian, additional, and Pöttgen, Rainer, additional

Published
2010
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210. Supraleitung in quasi-eindimensionalen Carbiden

Author

Scherer, Wolfgang, primary, Hauf, Christoph, additional, Presnitz, Manuel, additional, Scheidt, Ernst-Wilhelm, additional, Eickerling, Georg, additional, Eyert, Volker, additional, Hoffmann, Rolf-Dieter, additional, Rodewald, Ute C., additional, Hammerschmidt, Adrienne, additional, Vogt, Christian, additional, and Pöttgen, Rainer, additional

Published
2010
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247. Ca4Au10Zn3 - A Substitution Variant of AlB2 by Incorporation of Zn3 Triangles.

Author

Gerke, Birgit, Hoffmann, Rolf‐Dieter, and Pöttgen, Rainer

Subjects
*INTERMETALLIC compounds synthesis, *CALCIUM compounds, *TANTALUM, *X-ray crystallography, *THREE-dimensional imaging, *ARISTOTYPE
Abstract

The gold-rich intermetallic phase Ca4Au10Zn3 was synthesized from the elements by high-frequency melting in sealed tantalum ampoules. Analyses of the sample by X-ray powder and single crystal diffraction indicated a new structure type with a small homogeneity range resulting from Au/Zn mixing: C2/ c, a = 1598.4(2), b = 819.7(1), c = 1188.2(2) pm, β = 120.93(1)°, wR2 = 0.0397, 2292 F2 values, 83 variables for Ca4Au9.66(1)Zn3.34(1), and a = 1596.6(2), b = 818.8(2), c = 1187.1(2) pm, β = 120.91(2)°, wR2 = 0.0280, 2296 F2 values, 83 variables for Ca4Au9.98(1)Zn3.02(1). The gold atoms built up a three-dimensional distorted tetrahedral network with Au-Au distances ranging from 274-294 pm. The cavities within this network are filled by calcium atoms and Zn3 triangles (272-279 pm Zn-Zn) in an ordered manner. The small homogeneity range Ca4Au10- xZn3+ x concerns Au/Zn mixing within the triangles and the tetrahedral network as well. The crystal chemical relationship with the aristotype AlB2 is discussed on the basis of a group-subgroup scheme. [ABSTRACT FROM AUTHOR]

Published
2015
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248. The Gallides SrRh2Ga2, SrIr2Ga2, and Sr3Ir4Ga4.

Author

Seidel, Stefan, Schubert, Lea, Hoffmann, Rolf-Dieter, and Pöttgen, Rainer

Subjects
INTERMETALLIC compounds, CRYSTAL structure, GALLIUM, X-ray diffraction, STRONTIUM
Abstract

The gallides SrRh2Ga2, SrIr2Ga2, and Sr3Rh4Ga4 were obtained from the elements by induction melting and subsequent annealing. They were investigated by powder and single-crystal X-ray diffraction: CaRh2B2 type, Fddd, a = 573.2(1), b = 1051.3(1), c = 1343.7(2) pm, wR2 = 0.0218, 398 F2 values, 15 variables for SrRh2Ga2; a = 576.0(1), b = 1045.5(1), c = 1350.6(3) pm for SrIr2Ga2, and Na3Pt4Ge4 type, I $\bar{4}$3 m, a = 777.4(2) pm, wR2 = 0.0234, 190 F2 values, 11 variables for Sr3Ir4Ga4. The gallides SrRh2Ga2 and Sr3Ir4Ga4 exhibit complex, covalently bonded three-dimensional [Rh2Ga2] and [Ir4Ga4] networks with short Rh-Ga (241-246 pm) and Ir-Ga (243-259 pm) distances. The strontium atoms fill large cages within these networks. They are coordinated by 8 Rh + 10 Ga in SrRh2Ga2 and by 4 Ir + 8 Ga in Sr3Ir4Ga4. The structure of SrRh2Ga2 is discussed along with the monoclinic distortion variants HoNi2B2 and BaPt2Ga2 on the basis of a group-subgroup scheme. [ABSTRACT FROM AUTHOR]

Published
2015
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249. LaRh3Ga2 - Structure Determination from a Trilling.

Author

Seidel, Stefan, Hoffmann, Rolf‐Dieter, and Pöttgen, Rainer

Subjects
*X-ray diffraction, *CRYSTAL structure, *INTERMETALLIC compounds, *GALLIUM, *RHODIUM, *LANTHANUM
Abstract

The gallide LaRh3Ga2 was obtained by arc-melting of the elements and subsequent annealing of the product button in a high-frequency furnace. The sample was studied by powder X-ray diffraction and the structure was refined from single crystal data of a trilling: ErRh3Si2 type (CaCu5 superstructure), Imma, a = 760.1(2), b = 975.6(3), c = 564.0(2) pm, wR = 0.0358 for 717 F2 values and 23 variables; domain ratio 0.36(1) / 0.28(1) / 0.35(1). The rhodium atoms build up Kagomé networks (281.8 and 282.2 pm Rh-Rh), which are condensed through the gallium atoms (249.6-251.0 pm Rh-Ga). The lanthanum atoms fill large voids left by the three-dimensional [Rh3Ga2] network. They have coordination number 18 (6 Ga + 12 Rh) in form of a hexa-capped hexagonal prism. The crystal chemical relationship with the aristotype CaCu5 is briefly discussed on the basis of a group-subgroup scheme. [ABSTRACT FROM AUTHOR]

Published
2015
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250. New quaternary arsenide oxides with square planar coordination of gold(i) – structure, 197Au Mössbauer spectroscopic, XANES and XPS characterization of Nd10Au3As8O10 and Sm10Au3As8O10

Author

Bartsch, Timo, Niehaus, Oliver, Johrendt, Dirk, Kobayashi, Yasuhiro, Seto, Makoto, Abdala, Paula M., Bartsch, Manfred, Zacharias, Helmut, Hoffmann, Rolf-Dieter, Gerke, Birgit, Rodewald, Ute Ch., and Pöttgen, Rainer

Subjects
ARSENIDES, CHROMIUM-cobalt-nickel-molybdenum alloys, QUARTZ, RARE earth metals, COORDINATE covalent bond
Abstract

The quaternary gold(i) arsenide oxides Nd10Au3As8O10 and Sm10Au3As8O10 were synthesized in sealed quartz ampoules from the rare earth (RE) elements, their appropriate sesquioxides, arsenic, arsenic(iii) oxide and finely dispersed gold at maximum annealing temperatures of 1223 K. Both structures were refined from X-ray single crystal diffractometer data at room temperature and at 90 K. Nd10Au3As8O10 and Sm10Au3As8O10 crystallize with a new structure type that derives from the BaAl4 structure through distortions and formation of ordered vacancies. The structures consist of stacked polycationic [RE10O10]10+ layers with oxygen in tetrahedral rare earth coordination and polyanionic [Au(i)3(As2)4]10− layers with gold in square planar or rectangular planar coordination of four arsenic dumbbells (255 pm As1–As2). In contrast to the well known ionic rare earth oxide layers, the gold arsenide layers rather show covalent bonding and account for the metallic nature of these two new arsenide oxides. This is confirmed by electronic structure calculations and resistivity measurements. The oxidation state of gold was investigated by 197Au Mössbauer, X-ray absorption near edge structure (XANES) and photoelectron (XPS) spectroscopy. Due to missing comparative gold arsenide compounds, the monovalent gold phosphide oxides RE2AuP2O were measured for comparison. The XANES measurements additionally comprise monovalent gold arsenides REAuAs2. The XPS study contains BaAuAs as reference compound instead. Combination of all data clearly indicates Au(i), which was not observed in square planar coordination up to now. Temperature dependent magnetic susceptibility data show Curie–Weiss paramagnetism for Nd10Au3As8O10 and no magnetic ordering down to 2.5 K. Sm10Au3As8O10 shows the typical Van Vleck type paramagnetism for samarium compounds along with a transition to an antiferromagnetically ordered state at TN = 8.6 K. [ABSTRACT FROM AUTHOR]

Published
2015
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