Structural Frustration and Occupational Disorder: The Rare Earth Metal Polysulfides Tb₈S_14.8, Dy₈S_14.9, Ho₈S_14.9, and Y₈S_14.8

Dark red crystals of Y₈S_14.8, Tb₈S_14.8, Dy₈S_14.9, and Ho₈S_14.9 have been obtained following different reaction routes. The isostructural title compounds adopt the Gd₈Se₁₅ type, a 24-fold superstructure of the ZrSSi-type and can be described in space group <i>A</i>112 (non standard setting of <i>C</i>121, no. 5) with lattice parameter of <i>a</i> = 11.505(1) Å, <i>b</i> = 15.385(1) Å, <i>c</i> = 15.726(1) Å, and γ = 90.21(2)° for Y₈S_{15–<i>x</i>}; <i>a</i> = 11.660(1) Å, <i>b</i> = 15.468(2) Å, <i>c</i> = 15.844(2) Å, and γ = 90.19(2)° for Tb₈S_{15–<i>x</i>}; <i>a</i> = 11.584(1) Å, <i>b</i> = 15.340(2) Å, <i>c</i> = 15.789(2) Å, and γ = 90.34(2)° for Dy₈S_{15–<i>x</i>}; and <i>a</i> = 11.538(1) Å, <i>b</i> = 15.288(2) Å, <i>c</i> = 15.740(2) Å, and γ = 90.23(1)° for Ho₈S_{15–<i>x</i>}, respectively. The structure consists of an alternating stacking of puckered [<i>RE</i>S] (<i>RE</i>, rare-earth metals) double slabs and planar sulfur layers along [001]. The planar sulfur layers have a complex arrangement of S₂^2– dinuclear dianions, isolated S^2– ions, and vacancies. All compounds contain trivalent rare-earth metal ions, for Tb₈S_{15–<i>x</i>} and Dy₈S_{15–<i>x</i>} antiferromagnetic order was found at <i>T</i>_N = 5.4(2) K and 3.8(1) K, respectively. Short wavelength cutoff optical band gaps of 1.6 to 1.7 eV were determined

Structural Frustration and Occupational Disorder: The Rare Earth Metal Polysulfides Tb₈S_14.8, Dy₈S_14.9, Ho₈S_14.9, and Y₈S_14.8

Dark red crystals of Y₈S_14.8, Tb₈S_14.8, Dy₈S_14.9, and Ho₈S_14.9 have been obtained following different reaction routes. The isostructural title compounds adopt the Gd₈Se₁₅ type, a 24-fold superstructure of the ZrSSi-type and can be described in space group <i>A</i>112 (non standard setting of <i>C</i>121, no. 5) with lattice parameter of <i>a</i> = 11.505(1) Å, <i>b</i> = 15.385(1) Å, <i>c</i> = 15.726(1) Å, and γ = 90.21(2)° for Y₈S_{15–<i>x</i>}; <i>a</i> = 11.660(1) Å, <i>b</i> = 15.468(2) Å, <i>c</i> = 15.844(2) Å, and γ = 90.19(2)° for Tb₈S_{15–<i>x</i>}; <i>a</i> = 11.584(1) Å, <i>b</i> = 15.340(2) Å, <i>c</i> = 15.789(2) Å, and γ = 90.34(2)° for Dy₈S_{15–<i>x</i>}; and <i>a</i> = 11.538(1) Å, <i>b</i> = 15.288(2) Å, <i>c</i> = 15.740(2) Å, and γ = 90.23(1)° for Ho₈S_{15–<i>x</i>}, respectively. The structure consists of an alternating stacking of puckered [<i>RE</i>S] (<i>RE</i>, rare-earth metals) double slabs and planar sulfur layers along [001]. The planar sulfur layers have a complex arrangement of S₂^2– dinuclear dianions, isolated S^2– ions, and vacancies. All compounds contain trivalent rare-earth metal ions, for Tb₈S_{15–<i>x</i>} and Dy₈S_{15–<i>x</i>} antiferromagnetic order was found at <i>T</i>_N = 5.4(2) K and 3.8(1) K, respectively. Short wavelength cutoff optical band gaps of 1.6 to 1.7 eV were determined

Many Faces of Ni₃Bi₂S₂: Tunable Nanoparticle Morphology via Microwave-Assisted Nanocrystal Conversion

Several combinations of the microwave-assisted polyol route and conversion chemistry techniques were exploited to access the bimetallic sulfide Ni₃Bi₂S₂ with a variety of morphological features. First, Bi₂S₃ microstructures can be converted into Ni₃Bi₂S₂ at 240 °C; the precursor’s rod-like shape and size pertain to the final product. Second, round Ni₃Bi₂S₂ particles can be obtained directly from a presynthesized NiBi intermetallic precursor; the resultant submicron size particles agglomerate and thus differ from the starting alloy’s shape. Third, microwave reflux of bismuth nitrate and nickel acetate solution in ethylene glycol in the presence of thiosemicarbazide can be employed to produce Ni₃Bi₂S₂ with a peculiar flower-like morphology. The presence and the decisive role of the <i>in situ</i> generated NiBi intermediate are unraveled, confirming that the reaction proceeds via transformation of solid rather than via a solution–dissolution process. NiBi nanoparticles preconfigure the Ni₃Bi₂S₂ product morphology in a wide range of pH values. In turn, the pH value is found to be a key factor that determines the type of impurities accompanying the Ni₃Bi₂S₂ ternary phase. At pH ≈ 4 bismuth precipitates as a main side-phase, while pH ≈ 12 favors the formation of NiS impurity

Downscaling Effect on the Superconductivity of Pd₃Bi₂X₂ (X = S or Se) Nanoparticles Prepared by Microwave-Assisted Polyol Synthesis

Pd₃Bi₂S₂ and Pd₃Bi₂Se₂ have been successfully prepared in the form of nanoparticles with diameters of ∼50 nm by microwave-assisted modified polyol synthesis at low temperatures. The composition and morphology of the samples have been studied by means of powder X-ray diffraction as well as electron microscopy methods, including X-ray intensity mapping on the nanoscale. Superconducting properties of the as-prepared samples have been characterized by electrical resistivity measurements down to low temperatures (∼0.2 K). Deviations from the bulk metallic behavior originating from the submicrometer nature of the samples were registered for both phases. A significant critical-field enhancement up to 1.4 T, i.e., 4 times higher than the value of the bulk material, has been revealed for Pd₃Bi₂Se₂. At the same time, the critical temperature is suppressed to 0.7 K from the bulk value of ∼1 K. A superconducting transition at 0.4 K has been observed in nanocrystalline Pd₃Bi₂S₂. Here, a zero-temperature upper critical field of ∼0.5 T has been estimated. Further, spark plasma-sintered Pd₃Bi₂S₂ and Pd₃Bi₂Se₂ samples have been investigated. Their superconducting properties are found to lie between those of the bulk and nanosized samples

Synthesis of a Cu-Filled Rh₁₇S₁₅ Framework: Microwave Polyol Process Versus High-Temperature Route

Metal-rich, mixed copper–rhodium sulfide Cu_3−δRh₃₄S₃₀ that represents a new Cu-filled variant of the Rh₁₇S₁₅ structure has been synthesized and structurally characterized. Copper content in the [CuRh₈] cubic cluster was found to vary notably dependent on the chosen synthetic route. Full site occupancy was achieved only in nanoscaled Cu₃Rh₃₄S₃₀ obtained by a rapid, microwave-assisted reaction of CuCl, Rh₂(CH₃CO₂)₄ and thiosemicarbazide at 300 °C in just 30 min; whereas merely Cu-deficient Cu_3−δRh₃₄S₃₀ (2.0 ≥ δ ≥ 0.9) compositions were realized via conventional high-temperature ceramic synthesis from the elements at 950 °C. Although Cu_3−δRh₃₄S₃₀ is metallic just like Rh₁₇S₁₅, the slightly enhanced metal content has a dramatic effect on the electronic properties. Whereas the Rh₁₇S₁₅ host undergoes a superconducting transition at 5.4 K, no signs of the latter were found for the Cu-derivatives at least down to 1.8 K. This finding is corroborated by the strongly reduced density of states at the Fermi level of the ternary sulfide and the disruption of long-range Rh–Rh interactions in favor of Cu–Rh interactions as revealed by quantum-chemical calculations

Synthesis, Crystal and Topological Electronic Structures of New Bismuth Tellurohalides Bi₂TeBr and Bi₃TeBr

Halogen substitution, that is, bromine for iodine, in the series of topological Bi_<i>n</i>TeI (<i>n</i> = 1, 2, 3) materials was conducted in order to explore the impact of anion exchange on topological electronic structure. In this proof-of-concept study, we demonstrate the applicability of the modular view on crystal and electronic structures of new Bi₂TeBr and Bi₃TeBr compounds. Along with the isostructural telluroiodides, they constitute a family of layered structures that are stacked from two basic building modules, _∞²[Bi₂] and _∞²[BiTeX] (X = I, Br). We present solid-state synthesis, thermochemical studies, crystal growth, and crystal-structure elucidation of Bi₂TeBr [space group <i>R</i>3̅<i>m</i> (no. 166), <i>a</i> = 433.04(2) pm, <i>c</i> = 5081.6(3) pm] and Bi₃TeBr [space group <i>R</i>3<i>m</i> (no. 160), <i>a</i> = 437.68(3) pm, <i>c</i> = 3122.9(3) pm]. First-principles calculations establish the topological nature of Bi₂TeBr and Bi₃TeBr. General aspects of chemical bonding appear to be similar for Bi_<i>n</i>TeX (X = I, Br) with the same <i>n</i>, so that alternation of the global gap size upon substitution is insignificant. The complex topological inversion proceeds between the states of two distinct modules, _∞²[Bi₂] and _∞²[BiTeBr]; thus, the title compounds can be seen as heterostructures built via a modular principle. Furthermore, highly disordered as well as incommensurately modulated ternary phase(s) are documented near the Bi₂TeBr composition. Single-crystal X-ray diffraction experiments on BiTeBr and Bi₂TeI resolve some discrepancies in prior published work

Modular Design with 2D Topological-Insulator Building Blocks: Optimized Synthesis and Crystal Growth and Crystal and Electronic Structures of Bi_<i>x</i>TeI (<i>x</i> = 2, 3)

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. <i>R</i>3<i>m</i>, <i>a</i> = 440.12(2) pm, <i>c</i> = 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 Bi_<i>x</i>TeI with <i>x</i> > 3; instead, it indicates a possible homogeneity range of Bi₃TeI. The series BiTeI–Bi₂TeI–Bi₃TeI illustrates the influence of structural modifications on topological properties