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[en] Crystal structure determination of UPTe revealed a UGeTe derivative structure with a pseudo-tetragonal unit cell with lattice parameters a = 410.1(1) pm and c = 1697.1(1) pm at 120(2) K. ThPTe can be regarded as isotypic according to powder X-ray diffraction data, its pseudo-tetragonal lattice parameters are a = 425.05(1) pm and c = 1726.8(1) pm at 296(1) K. Real-space topological analysis of the chemical bonding and Raman data reveal the presence of P_2 units. U_2PTe_2O can be considered as a partially oxidised phosphide telluride with a pseudo-tetragonal unit cell, a = 403.7(1) pm, and c = 3206.8(10) pm at 120(2) K. Single-crystal X-ray diffraction data of UPTe and U_2PTe_2O indicate an ordered orientation of the P_2 dumbbells leading to a monoclinic distortion, which implies a symmetry decrease to space group I11m. (Copyright copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
[en] The reaction of the electrophilic transition metal iridium with tellurium, indium, and bromine resulted in black, shiny crystals with the composition [Ir_2Te_1_4Br_1_2]_2(InBr_4)_2. X-ray diffraction on single-crystals revealed a triclinic structure (space group P anti 1) that contains two crystallographically distinct, centrosymmetric clusters, (Te_1_0)[Ir(TeBr_3)_2]_2"+ and (Te_1_0)[Ir(TeBr_4)(TeBr_2)]_2"+, as well as two tetrahedral InBr_4"- anions per unit cell. The center of the positively charged cluster is a Te_1_0"."- radical anion. This biconvex tricyclo[188.8.131.52"3", "5] unit consists of two angulated Te_4 rings that are linked by two almost linear μ-Te bridges. The radical causes an intense single ESR signal at g = 1.999. Molecular DFT-calculations show that the unpaired electron populates an orbital of the Te_1_0-unit. Computational variation of the number of electrons causes noticeable variations in the Te-Te distances, providing strong evidence for the Te_1_0"."- radical. The decatellurium unit coordinates two iridium(III) cations as a bridging bis-tetradentate ligand. Two terminal bromidotellurate(II) groups complete the slightly distorted octahedral coordination of each transition metal atom. The two [IrTe_6] polyhedra share a common edge. The constitutions of the terminal ligands differ, including only TeBr_3"- anions in one type of clusters, but a combination of TeBr_4"2"- and TeBr_2 groups in the other. The coordinating tellurium atoms of the central Te_1_0"."- and of the terminal groups act as electron pair donors, thereby fulfilling the 18-electron-rule for the iridium(III) cations. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
[en] The Kitaev-Heisenberg model is source of a topological quantum spin liquid with Majorana fermions and gauge flux excitations as fractional quasiparticles. The material -RuCl is composed of weakly van der Waals bound honeycomb layers of edge sharing RuCl octahedra which has recently emerged as a prime candidate for realising such physics. We studied -RuCl by means of thermal transport measurements, a valuable tool to probe elementary excitations of systems with low dimensional spin structure. While the in-plane, longitudinal heat transport is governed by heat conduction of phonons that strongly scatter off the magnetic excitations present in the system, studying the thermal Hall effect (Rhighi-Leduc effect) opens up a new path towards detecting a direct contribution of unconventional magnetic excitations to entropy transport. We have observed a sizeable transversal heat conductivity , the agreement of which with the theoretical predictions for the pure Kitaev model being suggestive of heat transport by fractionalised quasiparticles in -RuCl.
[en] The pale‐pink, hygroscopic compounds Mn(OH)X (X = Br, I) were obtained by high‐pressure synthesis in a Walker‐type multianvil apparatus. They crystallize in the space group P2/c with a = 640.48(3), b = 698.80(3), c = 615.54(2) pm, β = 110.30(1)° at 183(1) K (X = Br), and a = 686.18(3), b = 713.08(3), c = 637.18(3) pm, β = 109.51(1)° at 150(1) K (X = I). The crystal structures are isotypic to Cu(OH)Cl and consist of edge‐sharing distorted Mn(OH)X octahedra arranged in sheets parallel to the bc‐plane. Spin‐polarized scalar‐relativistic DFT+U calculations predict an intrinsic magnetic insulating state (ca. 3.5 eV bandgap) that is proximate to frustration. Calculated effective magnetic moments equal to 4.34 μ/f.u. for Mn(OH)Br and 4.33 μ/f.u. for Mn(OH)I. FT‐IR spectroscopy confirmed interlayer hydrogen bonding. As a side result of the experiments, the compound trans‐MnBr·4HO was obtained. It crystallizes in the space group Cmcm with a = 438.64(2), b = 1167.84(6), and c = 730.95(4) pm. (© 2019 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
[en] The reaction of selenium and NbCl_5 with arsenic in the Lewis-acidic ionic liquid BMImCl.4.8AlCl_3 at 100 C yielded dark-red block-shaped crystals of Nb_2Se_4(AlCl_4)_4, which immediately decompose when exposed to humid air. Arsenic takes the part of the reducing agent for niobium as well as selenium. The crystal structure was described in the monoclinic space group P2_1/n (no. 14) with a = 898.0(1) pm, b = 991.3(1) pm, c = 1629.1(2) pm, and β = 92.43(1) at 296(1) K. The unit cell contains two C_2_h symmetric Nb_2(Se_2)_2(AlCl_4)_4 molecules. The latter consist of a central rectangular bipyramid [Nb_2(Se_2)_2]"4"+ and four η"2-coordinating AlCl_4"- tetrahedra. Diamagentism of the compound and DFT-based real-space bonding analysis imply a chemical bond between the niobium(IV) cations, which are 292.2(2) pm apart. Nb_2Se_4(AlCl_4)_4 can be interpreted as the AlCl_3 adduct of NbSe_2Cl_2. (Copyright copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
[en] The lanthanum-rich antimonide La2NiSb was synthesized by annealing a cold-pressed pellet of the elements in a sealed silica glas tube at 1120 K. La2NiSb was characterized by powder and single-crystal X-ray diffraction: ordered Bi3Ni type, Pnma, Z = 4, a = 825.6(3), b = 452.2(2), c = 1195.5(4) pm, wR = 0.0695, 856 F2 values, 26 variables. The nickel atoms form infinite zig-zag chains (259 pm Ni-Ni) with trigonal-prismatic lanthanum coordination for each nickel atom. The antimony atoms cap the rectangular faces of the lanthanum prisms (336 pm La-Sb) and thereby coordinate also the nickel atoms (271 pm Ni-Sb). These rods run parallel to the b axis and form a herringbone pattern, similar to the FeB-type structure of GdNi. Although metallic conductivity is expected for La2NiSb from DFT-based band structure calculations, the real-space bonding analysis shows prominent localization of electrons on antimonide anions and positively charged lanthanum cations. The chain substructure is strongly bonded by polar covalent Ni-Sb and multicenter Ni-Ni interactions. The nickel atoms, which are involved in multicenter bonding with adjacent nickel and lanthanum atoms, provide a conductivity pathway along the prismatic strands. 121Sb Moessbauer spectroscopic data at 78 K show a single signal at an isomer shift of -7.62(3) mm s-1, supporting the antimonide character. La2NiSb shows weak paramagnetism with a susceptibility of 2.5 x 10-3 emu mol-1 at room temperature.
[en] The interplay between electronic correlations and spin-orbit coupling in heavy transition metal compounds has been intensively studied in the last years due to their interesting properties and unusual ground states like quantum spin liquids. Particularly α-RuCl_3 seems to be a suitable candidate for the experimental realisation of the Kitaev-Model due to its J_e_f_f = 1/2 state and its layered honeycomb lattice of Ru"3"+ ions in the 4d"5 configuration. This leads to highly anisotropic magnetic properties in this compound. We report on specific heat and magnetisation measurements for α-RuCl_3 single crystals grown by means of chemical transport reactions. Furthermore magnetisation experiments under high pressure were conducted on this compound.
[en] -RuCl crystallizes in a layered honeycomb structure and has been proposed as a candidate to realize a fractionalized Kitaev model with strongly frustrated, bond-dependent, anisotropic interactions between Ru magnetic moments (j = ). By introducing Cr as dopant to this Mott insulator (S = at the Ru sites), one can investigate changes of the long-range order in the ground state of -RuCl as well as of the anisotropic Kitaev interactions and field-induced effects which appear upon doping. We report on susceptibility and specific heat measurements of RuCrCl, probing the effect of different doping levels on the magnetic and thermodynamic properties on single crystals for the full range 0 x 1.
[en] Uniform nanocrystals of the intermetallic compounds Bi_2Ir (diameter ≥ 50 nm) and Bi_3Ni (typical size 200 x 600 nm) were obtained by a microwave-assisted polyol process at 240 C. The method was also applied to the spatially confined reaction environment in the microporous exo-template SBA-15 resulting in Bi_3Ni particles of about 6 nm. Non-crystalline bundles of parallel Bi_3Ni nanofibres that have an individual diameter of less than 1 nm were obtained by reductive pseudomorphosis of the subiodide Bi_1_2Ni_4I_3 at room temperature. Magnetic susceptibility measurements demonstrate coexistence of ferromagnetism and superconductivity in a single phase for the nanostructured Bi_3Ni materials. Curie temperature, coercive field, remnant magnetization, saturation moment, diamagnetic screening, and critical field vary with particle size. The crystal structure of Bi_2Ir was determined by Rietveld refinement of powder X-ray diffraction data. Bi_2Ir crystallizes in the monoclinic arsenopyrite type (space group P2_1/c), a superstructure of the markasite type, with a = 690.11(1), b = 678.85(1), c = 696.17(1) pm, and β = 116.454(1) . In contrast to most of the other phases of this type, the Bi_2Ir is not a diamagnetic semiconductor but a weakly paramagnetic semimetal. Conductivity measurements down to 4 K and magnetization measurements in a field of μ_0H = 10 mT down to 1.8 K give no evidence for a transition into the superconducting state. Bonding analysis shows prevailing contribution of Bi-Bi interactions to the conduction, whereas Bi-Ir bonding is mostly covalent and localized. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
[en] Topologically ordered states of matter have recently gained much attention due to their novel physical properties, the signatures of which can be experimentally probed. A prime example is the spin liquid realized in the Kitaev honeycomb lattice compass model, where fractionalization of particles leads to broad continuum-like features in the magnetic response. We will present the high-field microwave absorption results on the Mott-Hubbard-insulating material -RuCl which is, due to its structure and strong spin-orbit coupling, a promising candidate for the realization of Kitaev physics. Measurements on a single-crystal were conducted over a frequency range of = 70-660 GHz at temperatures ranging from 3-30 K. Strikingly, in addition to previously observed conventional gapped magnon modes, we find a highly unusual broad continuum characteristic of fractionalization which extends to energies below the lowest sharp mode and to temperatures significantly higher than the ordering temperature.