Through single-step solid-state reactions, a series of novel bichalcogenides with the general composition (LiFe)ChO (Ch = S, Se, Te) are successfully synthesized. (LiFe)ChO (Ch = S, Se) possess cubic anti-perovskite crystal structures, where Fe and Li are completely disordered on a common crystallographic site (3c). According to Goldschmidt calculations, Li and Fe are too small for their common atomic position and exhibit large thermal displacements in the crystal structure models, implying high cation mobility. Both compounds (LiFe)ChO (Ch = S, Se) were tested as cathode materials against graphite anodes (single cells); They perform outstandingly at very high charge rates (270 mA g, 80 cycles) and, at a charge rate of 30 mA g, exhibit charge capacities of about 120 mA h g. Compared to highly optimized LiCoO cathode materials, these novel anti-perovskites are easily produced at cost reductions by up to 95% and, yet, possess a relative specific charge capacity of 75%. Moreover, these iron-based anti-perovskites are comparatively friendly to the environment and (LiFe)ChO (Ch = S, Se) melt congruently; the latter is advantageous for manufacturing pure materials in large amounts.

A new monoclinic phase (m2) of ternary diamond-like compound Cu2SnSe3 was synthesized by reaction of the elements at 850 K. The crystal structure of m2-Cu2SnSe3 was determined through electron diffraction tomography and refined by full-profile techniques using synchrotron X-ray powder diffraction data (space group Cc, a = 6.9714(2) Å, b = 12.0787(5) Å, c = 13.3935(5) Å, β = 99.865(5)°, Z = 8). Thermal analysis and annealing experiments suggest that m2-Cu2SnSe3 is a low-temperature phase, while the high-temperature phase has a cubic crystal structure. According to quantum chemical calculations, m2-Cu2SnSe3 is a narrow-gap semiconductor. A study of the chemical bonding, applying the electron localizability approach, reveals covalent polar Cu-Se and Sn-Se interactions in the crystal structure. Thermoelectric properties were measured on a specimen consolidated using spark plasma sintering (SPS), confirming the semiconducting character. The thermoelectric figure of merit ZT reaches a maximum value of 0.33 at 650 K.

A new monoclinic selenide Cu 5 Sn 2 Se 7 was synthesized, and its crystal and electronic structure as well as thermoelectric properties were studied. The crystal structure of Cu 5 Sn 2 Se 7 was determined by electron diffraction tomography and refined by full-profile techniques using synchrotron X-ray powder diffraction data: space group C2, a = 12.6509(3) Å, b = 5.6642(2) Å, c = 8.9319(4) Å, β = 98125(4)°, Z = 2; T = 295 K. Thermal analysis and high-temperature synchrotron X-ray diffraction indicated the decomposition of Cu 5 Sn 2 Se 7 at 800 K with formation of the tetragonal high-temperature phase Cu 4.90(4) Sn 2.10(4) Se 7 : space group I4̅ 2m, a = 5.74738(1) Å, c = 11.45583(3) Å; T = 873 K. Both crystal structures are superstructures to the sphalerite type with tetrahedral coordination of the atoms. In agreement with chemical bonding analysis and band structure calculations, Cu 5 Sn 2 Se 7 exhibits metal-like electronic transport behavior.

Engineering of nanoscale structures is a requisite for controlling the electrical and thermal transport in solids, in particular for thermoelectric applications that require a conflicting combination of low thermal conductivity and low electrical resistivity. We report the thermoelectric properties of spark plasma sintered Magnéli phases WO2.90 and WO2.722. The crystallographic shear planes, which are a typical feature of the crystal structures of Magnéli-type metal oxides, lead to a remarkably low thermal conductivity for WO2.90. The figures of merit (ZT = 0.13 at 1100 K for WO2.90 and 0.07 at 1100 K for WO2.722) are relatively high for tungsten-oxygen compounds and metal oxides in general. The electrical resistivity of WO2.722 shows a metallic behaviour with temperature, while WO2.90 has the characteristics of a heavily doped semiconductor. The low thermopower of 80 μV K(-1) at 1100 K for WO2.90 is attributed to its high charge carrier concentration. The enhanced thermoelectric performance for WO2.90 compared to WO2.722 originates from its much lower thermal conductivity, due to the presence of crystallographic shear and dislocations in the crystal structure. Our study is a proof of principle for the development of efficient and low-cost thermoelectric materials based on the use of intrinsically nanostructured materials rather than artificially structured layered systems to reduce lattice thermal conductivity.

The production of hydrogen via water electrolysis is feasible only if effective and stable catalysts for the oxygen evolution reaction (OER) are available. Intermetallic compounds with well‐defined crystal and electronic structures as well as particular chemical bonding features are suggested here to act as precursors for new composite materials with attractive catalytic properties. Al2Pt combines a characteristic inorganic crystal structure (anti‐fluorite type) and a strongly polar chemical bonding with the advantage of elemental platinum in terms of stability against dissolution under OER conditions. We describe here the unforeseen performance of a surface nanocomposite architecture resulting from the self‐organized transformation of the bulk intermetallic precursor Al2Pt in OER.

Novel bichalcogenides with the general composition (Li2TM)­ChO (TM = Mn, Co; Ch = S, Se) were synthesized by single-step solid-state reactions. These compounds possess cubic anti-perovskite crystal structure with Pm3̅m symmetry; TM and Li are disordered on the crystallographic site 3c. According to Goldschmidt tolerance factor calculations, the available space at the 3c site is too large for Li+ and TM2+ ions. As cathode materials, all title compounds perform less prominent in lithium-ion battery setups in comparison to the already known TM = Fe homologue; e.g., (Li2Co)­SO has a charge density of about 70 mAh g–1 at a low charge rate. Nevertheless, the title compounds extend the chemical flexibility of the anti-perovskites, revealing their outstanding chemical optimization potential as lithium battery cathode material.

The spark-plasma-sintering (SPS) technique has successfully been applied for the single-step direct synthesis of Ti2O3 from a mixture of powders of rutile/anatase with titanium. The components react by diffusion through the grain boundaries, forming several intermediate phases locally. A single-phase material of titanium(III) oxide is obtained in compact bulk form after 180 min of SPS treatment at 1473 K. The electrical and thermal transport properties of such a SPS-prepared material measured in the temperature range between 300 and 800 K reflect the known semiconductor-to-metal transition above 400 K. The observed metallic-like electrical and thermal conductivity above this temperature is in good agreement with previously reported results. A maximum of the thermoelectric figure-of-merit ZT = 0.04 is achieved at 350 K.

The chemical behavior of CaAg as catalyst for ethylene epoxidation was studied using a combination of experimental (X-ray powder diffraction, scanning electron microscopy, thermal analysis and infrared spectroscopy), and quantum chemical techniques as well as real-space chemical bonding analysis. Under oxidative ethylene epoxidation conditions, the CaAg (010) surface possesses an outstanding stability during long-term experiments. It is caused by the formation of an ordered, stable and dense CaO passivation layer with a small amount of embedded Ag atoms. On this way, the (010) surface constitutes a kinetic barrier for further incorporation of oxygen into the subsurface region and thereby prevents  further oxidative decomposition of CaAg. The calculated adsorption energies of the reaction species show strong adsorption of the reaction products that may explain the observed low conversion of ethylene toward ethylene oxide using CaAg as catalyst.