Oliver Osters

Synthesis and Identification of Metastable Compounds: Black Arsenic—Science or Fiction?†

Back in black: All metastable and stable phases can be identified for the solid solution arsenic/phosphorus by a combination of quantum-chemical calculations and investigations of the phase formation. Reaction paths for phase formations and transitions in situ were also evaluated. The results show that orthorhombic black arsenic (o-As) is metastable in pure form and has only been previously obtained by stabilizing impurities.

Cd4Cu7As, The First Representative of a Fully Ordered, Orthorhombically Distorted MgCu2 Laves Phase

The ternary Laves phase Cd(4)Cu(7)As is the first intermetallic compound in the system Cu-Cd-As and a representative of a new substitution variant for Laves phases. It crystallizes orthorhombically in the space group Pnnm (No. 58) with lattice parameters a = 9.8833(7) Å; b = 7.1251(3) Å; c = 5.0895(4) Å. All sites are fully occupied within the standard deviations. The structure can be described as typical Laves phase, where Cu and As are forming vertex-linked tetrahedra and Cd adopts the structure motive of a distorted diamond network. Cd(4)Cu(7)As was prepared from stoichiometric mixtures of the elements in a solid state reaction at 1000 °C. Magnetic measurements are showing a Pauli paramagnetic behavior. During our systematical investigations within the ternary phase triangle Cd-Cu-As the cubic C15-type Laves phase Cd(4)Cu(6.9(1))As(1.1(1)) was structurally characterized. It crystallizes cubic in the space group Fd3m with lattice parameter a = 7.0779(8) Å. Typically for quasi-binary Laves phases Cu and As are both occupying the 16c site. Chemical bonding, charge transfer and atomic properties of Cd(4)Cu(7)As were analyzed by band structure, ELF, and AIM calculations. On the basis of the general formula for Laves phases AB(2), Cd is slightly positively charged forming the A substructure, whereas Cu and As represent the negatively charged B substructure in both cases. The crystal structure distortion is thus related to local effects caused by Arsenic that exhibits a larger atomic volume (18 Å(3) compared to 13 Å(3) for Cu) and higher ionicity in bonding.

Silver(I)-(poly)chalcogenide Halides – Ion and Electron High Potentials

Abstract Materials with high dynamics in the solid state are of potential interest in semiconductor science and for a great variety of energy applications. In most of the cases the majority of physical properties of such compounds are directly related to their electronic structure. Optimization of properties is therefore correlated with direct or indirect control of this parameter. Compounds with highly mobile ions like the coinage metal cations and the heavy chalcogenide anions can easily be modified chemically or physically to fine tune their electronic structures. The range of adjustable properties lasts from ion conductivity, magneto resistance, thermoelectricity to a reversible redox-driven switch of semiconductivity. Today, the strong demand on clean energy production, the efficient energy transport and energy storage is a major goal for present and oncoming generations. Stable, mixed-conducting materials will play a major role in this process. The ongoing development of coinage metal chalcogenide halides during the last 50 years reflects the fundamental interest in this field. Many interesting and sometimes unexpected properties have been determined recently which substantiates the great potential of this class of materials. Especially the new class of coinage metal polychalcogenide halides is of potential interest due to their drastic modulations of physical properties driven by a fundamental tuning of its electronic structures. Thermopower and thermal diffusivity, two major properties to tune thermoelectricity can be varied in such a way that drastic changes can be addressed in very small temperature ranges close to room temperature. Herein we report on the recent progress of polychalcogenide and chalcogenide halides with the mobile d10 ions Ag and Cu putting the main focus on silver compounds.

Element allotropes and polyanion compounds of pnicogenes and chalcogenes: stability, mechanisms of formation, controlled synthesis and characterization

Abstract The application of the EnPhaSyn (theoretical Energy diagrams, experimental Phase formation, Synthesis and characterisation) concept is reviewed with respect to prediction of structures and stability of element allotropes and compound polymorphs, their phase formation and transition processes, and their directed synthesis, respectively. Therein, the relative energetical stability (En) of target compounds and possible decomposition are determined from quantum chemical DFT calculations. Phase formation and transition (Pha) is probed by a gas balance method, developed as high temperature gas balance concept. It helped to study the synthesis and stability range of several compounds experimentally. Applications of the concept and synthesis principles (Syn) of non-equilibrium phases are presented for allotropes of P, As, P1-xAsx, as well as binary and ternary compounds including the Zintl and Laves like phases IrPTe, NiP2, CoSbS, NiBiSe, Li0.2CdP2, Cu3CdCuP10, and Cd4Cu7As.

Zirconium Transition Metal (Poly)antimonides – Syntheses, Characterization and Electrochemical Properties

Herein we report on the syntheses, crystal structures and first electrochemical characterizations of ternary zirconium transition metal (poly)antimonides Zr2TSb3 (with T = Cu, Pd) and Zr3TSb7 (with T = Ni, Pd). The compounds were synthesized by arc-melting, followed by an annealing procedure at elevated temperatures. Phase analysis and structure analysis were performed by powder and singlecrystal measurements. The electrochemical properties of all compounds were measured in half cells against lithium to test their potential as anode materials for Li batteries. The Zr3TSb7 phases show metallic behavior with conductivities of 10-1 S cm-1 within a temperature range of 324 to 428 K Graphical Abstract Zirconium Transition Metal (Poly)antimonides – Syntheses, Characterization and Electrochemical Properties

The layered polyphosphide Ag3.73(4)Zn2.27(4)P16.

The silver zinc hexadecaphosphide Ag3.73(4)Zn2.27(4)P16 is the first polyphosphide in the ternary system Ag/Zn/P. It was synthesized from stoichiometric mixtures of Ag, Zn and P in the molar ratio 4:2:16, using AgI as a mineralizing agent in a gas-phase-assisted reaction. Ag3.73(4)Zn2.27(4)P16 crystallizes in the Cu5InP16 structure type. The asymmetric unit contains two Ag/Zn sites with mixed occupancies and four P sites. One of the Ag/Zn sites is located on a twofold rotation axis. The polyanionic [P16]-substructure consists of corrugated six-membered rings that are connected into a layer via the 1-, 2-, 4- and 5-positions of the rings by a bridging P atom in each case. The layers extend parallel to the bc plane and are stacked along the a axis. Both Ag/Zn sites are tetrahedrally coordinated by P atoms.

Cu4.35Cd1.65As16: the first polyarsenic compound in the Cu–Cd–As system

The first polyarsenic compound in the Cu–Cd–As system was obtained by solid-state reaction of the elements and has a refined composition of Cu4.35 (2)Cd1.65 (2)As16 (tetracopper dicadmium hexadecaarsenide). It adopts the Cu5InP16 structure type. The asymmetric unit consists of one Cu site, a split Cu/Cd site and four As sites. The polyanionic structure can be described as being composed of As6 rings in chair conformations which are connected in the 1-, 2-, 4- and 5-positions. The resulting layers evolve along the c axis perpendicular to the ab plane. One Cu atom exhibits site symmetry 2 and is tetrahedrally coordinated by four As atoms. The other Cu atom, representing the split site, and the corresponding Cd atom have different coordination spheres. While the Cu atom is tetrahedrally coordinated by four As atoms, the Cd atom has a [3 + 1] coordination with a considerably longer Cd—As distance.