Refine
Document Type
Keywords
- Bismuth layered compounds (1)
- Crystal structure (1)
- Crytal growth (1)
- Electronic structure (1)
- Topological insulator (1)
- bismuth (1)
- cluster compounds (1)
- hexagonal perovskite (1)
- ionic liquids (1)
- low-valen (1)
Institute
BTU
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 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.
Out-of-the-box Multipath TCP as a Tor Transport Protocol: Performance and Privacy Implications
(2020)
This study is based on 616 geochronological ages from aeolian
and colluvial sediments as well as paleosols, representing the
largest database of geochronological data from northeastern
Germany available to date. Cumulative probability density functions
for radiocarbon data and kernel density estimates for luminescence
data were created covering the last 15 ka. The data analysis aimed at the identification of changes and their drivers in geomorphodynamics and soil formation. The ages representing
aeolian activity cluster in the Late Glacial, the Early Holocene, and the Late Holocene, where the first two clusters are assumed to
result mostly from climatic impact with only a minor share of
human impact triggering the mobilization of aeolian sediments.
The third cluster is considered to result mainly from human
impact. The Late Glacial to Early Holocene activity phase is interrupted by a phase of surface stability around 11.5–12.7 ka, which is indicated by the occurrence of initial soil formations of Finow and Usselo types. Colluvial sedimentation predominantly occurred during the last 7 ka and clearly accelerated since the last 1000 a. According to the ages of specific paleosol types, related soilforming processes started already in the Late Glacial and were
completed in the Holocene.