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Institute
Gadolinium disulfide was prepared by high-pressure synthesis at 8 GPa and 1173 K. It crystallizes in the monoclinic space group P121/a1 (No. 14) with lattice parameters a = 7.879(1) Å; b = 3.936(1) Å, c = 7.926(1) Å and β = 90.08(1)°. The crystal structure is a twofold superstructure of the aristotype ZrSSi and consists of puckered cationic [GdS]+ double slabs that are sandwiched by planar sulfur sheets containing S22– dumbbells. The thermal decomposition of GdS2 proceeds via the sulfur-deficient polysulfides GdS1.9, GdS1.85 and GdS1.77 and eventually results in the sesquisulfide Gd2S3. GdS2 is a paramagnetic semiconductor which orders antiferromagnetically at TN = 7.7(1) K. A metamagnetic transition is observed in the magnetically ordered state.
Structural engineering of topological bulk materials is systematically explored with regard to the incorporation of the buckled bismuth layer [Bi₂], which is a 2D topological insulator per se, into the layered BiTeI host structure. The previously known bismuth telluride iodides, BiTeI and Bi₂TeI, offer physical properties relevant for spintronics. Herewith a new cousin, Bi₃TeI (sp.gr. R3m, a = 440.12(2) pm, c = 3223.1(2) pm), joins the ranks and expands this structural family. Bi₃TeI = [Bi₂][BiTeI] represents a stack with strictly alternating building blocks. Conditions for reproducible synthesis and crystal-growth of Bi₂TeI and Bi₃TeI are ascertained, thus yielding platelet-like crystals on the millimeter size scale and enabling direct measurements. The crystal structures of Bi₂TeI and Bi₃TeI are examined by X-ray diffraction and electron microscopy. DFT calculations predict metallic properties of Bi₃TeI and an unconventional surface state residing on various surface terminations. This state emerges as a result of complex hybridization of atomic states due to their strong intermixing. Our study does not support the existence of new stacking variants BiₓTeI with x > 3; instead, it indicates a possible homogeneity range of Bi₃TeI. The series BiTeI–Bi₂TeI–Bi₃TeI illustrates the influence of structural modifications on topological properties.
The crystallization mechanism of uranium phosphide telluride UPTe by chemical vapor transport reaction [1] is presented based on thermodynamic modelling using TRAGMIN program. Evaluation of standard data of all expected species was performed by modeling of the binary phase diagrams U/Te and U/P. Data of UPTe were deduced from known phosphide tellurides[2,3]. Identifying the viable composition area within the quaternary system U/P/Te/I the temperature depending transport equilibria could be obtained.
The reaction of Bi, BiCl₃, and TlCl in the ionic liquid [BMIm]Cl·4AlCl₃ (BMIm = 1-n-butyl-3-methylimidazolium) at 180 °C yielded air-sensitive black crystals of (Bi₈)Tl[AlCl₄]₃. X-ray diffraction on single crystals at room temperature revealed a structure containing [Tl(AlCl₄)₃]∞12−
strands separated by isolated Bi₈²⁺ square antiprisms. The thallium(I) ion is coordinated by twelve Cl⁻ ions of six [AlCl₄]⁻ groups, resulting in a chain of face-sharing [TlCl₁₂]¹¹⁻ icosahedra. The Bi₈²⁺ polycation is disordered, simulating a threefold axis through its center and overall hexagonal symmetry (space group P6₃/m). Slowly cooling the crystals to 170 K resulted in increased order in the Bi₈ cluster orientations. An ordered structure model in a supercell with a’ = 2a, b’ = 2b, c’ = 3c and the space group P6₅ was refined. The structure resembles a hexagonal perovskite, with complex groups in place of simple ions.
Single crystals of the polytellurides RETe1.8 of gadolinium, terbium, and dysprosium were prepared by chemical vapor transport and alkali metal halide flux reactions. To determine proper synthesis conditions for the desired target composition, the binary phase diagram Gd-Te was evaluated by CalPhaD methods. The compounds are isostructural to SmTe1.8 and crystallize in space group P4/n (no. 85) with lattice parameters of a = 966.10(4), 960.00(3), and 957.33(2) pm and c = 1794.15(10), 1785.77(6), and 1779.38(5) pm for GdTe1.8, TbTe1.8 and DyTe1.8, respectively. The structures consist of puckered [RETe] double slabs and planar telluride layers composed of Te2 dumbbells and linear Te3 units in accordance with ELI-D based bonding analyses. The latter can be understood as a Te3(4–) anion. GdTe1.8 is a semiconductor with a bandgap of 0.19 eV/0.17 eV (experimental / calculated). Magnetization data confirm trivalent RE ions and indicate antiferromagnetic order at T(N) = 12 K for TbTe1.8 and T(N) = 9.8 K for DyTe1.8, whereas GdTe1.8 remains paramagnetic down to 2 K.