Bertold Rasche

A Metallic Room‐Temperature Oxide Ion Conductor

Nanoparticles of Bi3 Ir, obtained from a microwave-assisted polyol process, activate molecular oxygen from air at room temperature and reversibly intercalate it as oxide ions. The closely related structures of Bi3 Ir and Bi3 IrOx (x≤2) were investigated by X-ray diffraction, electron microscopy, and quantum-chemical modeling. In the topochemically formed metallic suboxide, the intermetallic building units are fully preserved. Time- and temperature-dependent monitoring of the oxygen uptake in an oxygen-filled chamber shows that the activation energy for oxide diffusion (84 meV) is one order of magnitude smaller than that in any known material. Bi3 IrOx is the first metallic oxide ion conductor and also the first that operates at room temperature.

The Topochemical Pseudomorphosis of a Chloride into a Bismuthide

The heterogeneous reaction of crystals of the novel intermetallic subhalide Bi12 Rh3 Cl2 with a solution of n-butyllithium at 70 °C led to the complete topochemical exchange of chloride ions for bismuth atoms, that is, the transformation into the isostructural metastable intermetallic superconductor Bi14 Rh3. The crystals underwent the reductive pseudomorphosis almost unchanged except some fissures perpendicular to the a-axis. Detailed inspections of the transformed crystals by electron microscopy indicated no volume defects that would indicate internal chemical reactions. Thus, extensive mass transport must have occurred through the seemingly dense crystal structure. An efficient transport mechanism, based on an unusual breathing mode of the three-dimensional network formed by edge-sharing [RhBi8 ] cubes and antiprisms, is proposed. The replacement of ionic interaction in the chloride by metallic bonding in the binary intermetallic compound closes the pseudo gap in the density of states at the Fermi level. As a result, the rod-packing of conducting, yet electrically isolated strands of [RhBi8] cubes in Bi12 Rh3 Cl2 turns into the three-dimensional metal Bi14 Rh3.

Low-Temperature Topochemical Transformation of Bi13Pt3I7 into the New Layered Honeycomb Metal Bi12Pt3I5

Ordered single-crystals of the metallic subiodide Bi13 Pt3 I7 were grown and treated with n-butyllithium. At 45 °C, complete pseudomorphosis to Bi12 Pt3 I5 was achieved within two days. The new compound is air-stable and contains the same

Correlation between topological band character and chemical bonding in a Bi14Rh3I9-based family of insulators

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High-Temperature-Phase Bi4RhI2: Electronic Localization by Structural Distortion

[(PtBi8/2 )3 I](n+) honeycomb nets and iodide layers as the starting material Bi13 Pt3 I7 , but does not include

Stacked topological insulator built from bismuth-based graphene sheet analogues

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Bismuth‐based candidates for topological insulators: Chemistry beyond Bi2Te3

[BiI2 I4/2 ](-) iodidobismuthate strands. Electron microscopy and X-ray diffraction studies of solid intermediates visualize the process of the topochemical crystal-to-crystal transformation. In the electronic band structures of Bi13 Pt3 I7 and Bi12 Pt3 I5 , the vicinities of the Fermi levels are dominated by the intermetallic fragments. Upon the transformation of Bi13 Pt3 I7 into Bi12 Pt3 I5 , the intermetallic part is oxidized and the Fermi level is lowered by 0.16 eV. Whereas in Bi13 Pt3 I7 the intermetallic layers do not interact across the iodidobismuthate spacers (two-dimensional metal), they couple in Bi12 Pt3 I5 and form a three-dimensional metal.

Crystal Growth and Real Structure Effects of the First Weak 3D Stacked Topological Insulator Bi14Rh3I9

Recently the presence of topologically protected edge-states in Bi14Rh3I9 was confirmed by scanning tunnelling microscopy consolidating this compound as a weak 3D topological insulator (TI). Here, we present a density-functional-theory-based study on a family of TIs derived from the Bi14Rh3I9 parent structure via substitution of Ru, Pd, Os, Ir and Pt for Rh. Comparative analysis of the band-structures throughout the entire series is done by means of a unified minimalistic tight-binding model that evinces strong similarity between the quantum-spin-Hall (QSH) layer in Bi14Rh3I9 and graphene in terms of -molecular orbitals. Topologically non-trivial energy gaps are found for the Ir-, Rh-, Pt- and Pd-based systems, whereas the Os- and Ru-systems remain trivial. Furthermore, the energy position of the metal -band centre is identified as the parameter which governs the evolution of the topological character of the band structure through the whole family of TIs. The -band position is shown to correlate with the chemical bonding within the QSH layers, thus revealing how the chemical nature of the constituents affects the topological band character.

Electronic Structure of the Dark Surface of the Weak Topological Insulator Bi14Rh3I9

The metal-rich compound Bi4RhI2 was discovered in a thorough investigation of the Bi-Rh-I phase system. The monoclinic crystal structure was solved via single-crystal X-ray diffraction. It consists of infinite strands of face-sharing distorted square antiprisms ∞1[RhBi8/2]2+, which are separated by iodide ions. Bi4RhI2 is the high-temperature phase related to the weak three-dimensional topological insulator Bi14Rh3I9 (Bi4.67RhI3) and forms peritectically at 441 °C, where Bi14Rh3I9 decomposes. The structure of Bi4RhI2 is compared with Bi4RuI2 and Bi9Rh2I3, all three sharing a similar intermetallic strand-like structure, although their overall count of valence electrons differs. A chemical bonding analysis of Bi4RhI2 via the electron localizability indicator reveals a complex bonding pattern with covalent bonds between rhodium and bismuth, as well as between bismuth atoms and suggests a possible explanation for the formation of this structure type. Band structure calculations indicate a narrow band gap of 157 meV, which was verified by resistivity measurements on a pressed powder pellet and on single crystals. In a broader context, this strandlike structure type accounts for unusual physical phenomena, such as the transition into a charge-density-wave phase.