A solid solution strategy helps increase the efficiency of Ce3+ oxyfluoride phosphors for solid‐state white lighting. The use of a phosphor‐capping architecture provides additional light extraction. The accompanying image displays electroluminescence spectra from a 434‐nm InGaN LED phosphor that has been capped with the oxyfluoride phosphor.

Tetraborides of chromium and manganese exhibit an unusual boron-atom framework that resembles the hypothetical tetragonal diamond. They are believed to be very hard. Single crystals of MnB4 have now been grown. The compound crystallizes in the monoclinic crystal system (space group P21 /c) with a structure that has four crystallographically independent boron-atom positions, as confirmed by (11) B MAS-NMR spectroscopy. An unexpected short distance between the Mn atoms suggests a double Mn-Mn bond and is caused by Peierls distortion. The structure was solved using group-subgroup-relationships. DFT calculations indicate Mn(I) centers and paramagnetism, as confirmed by magnetic measurements. The density of states shows a pseudo-band gap at the Fermi energy and semiconducting behavior was observed for MnB4 .

Chromium tetraboride [orthorhombic, space group Pnnm (No. 58), a = 474.65(9) pm, b = 548.0(1) pm, c = 286.81(5) pm, and R value (all data) = 0.041], formerly described in space group Immm, was found not to be superhard, despite several theory-based prognoses. CrB(4) shows an almost temperature-independent paramagnetism, consistent with low-spin Cr(I) in a metallic compound. Conductivity measurements confirm the metallic character.

Inorganic materials with organic constituents-hybrid materials-have shown incredible promise as chemically tunable functional materials with interesting optical and electronic properties. Here, the preparation and structure are reported of two hybrid materials containing the optoelectronically active tropylium ion within tin- and lead-iodide inorganic frameworks with distinct topologies. The crystal structures of tropylium tin iodide, (C7H7)2SnI6, and tropylium lead iodide, C7H7PbI3, were solved using high-resolution synchrotron powder X-ray diffraction informed by X-ray pair distribution function data and high-resolution time-of-flight neutron diffraction. Tropylium tin iodide contains isolated tin(IV)-iodide octahedra and crystallizes as a deep black solid, while tropylium lead iodide presents one-dimensional chains of face-sharing lead(II)-iodide octahedra and crystallizes as a bright red-orange powder. Experimental diffuse reflectance spectra are in good agreement with density functional calculations of the electronic structure. Calculations of the band decomposed charge densities suggest that the deep black color of tropylium tin iodide is attributed to iodide ligand to tin metal charge transfer, while the bright red-orange color of tropylium lead iodide arises from charge transfer between iodine and tropylium states. Understanding the origins of the observed optoelectronic properties of these two compounds, with respect to their distinct topologies and organic-inorganic interactions, provides insight into the design of tropylium-containing compounds for potential optical and electronic applications.

Solid-state diffusion is often the primary limitation in the synthesis of crystalline inorganic materials and prevents the potential discovery and isolation of new materials that may not be the most stable with respect to the reaction conditions. Synthetic approaches that circumvent diffusion in solid-state reactions are rare and often allow the formation of metastable products. To this end, we present an in situ study of the solid-state metathesis reactions MCl2 + Na2S2 → MS2 + 2 NaCl (M = Fe, Co, Ni) using synchrotron powder X-ray diffraction and differential scanning calorimetry. Depending on the preparation method of the reaction, either combining the reactants in an air-free environment or grinding homogeneously in air before annealing, the barrier to product formation, and therefore reaction pathway, can be altered. In the air-free reactions, the product formation appears to be diffusion limited, with a number of intermediate phases observed before formation of the MS2 product. However, grinding the reactants in air allows NaCl to form directly without annealing and displaces the corresponding metal and sulfide ions into an amorphous matrix, as confirmed by pair distribution function analysis. Heating this mixture yields direct nucleation of the MS2 phase and avoids all crystalline binary intermediates. Grinding in air also dissipates a large amount of lattice energy via the formation of NaCl, and the crystallization of the metal sulfide is a much less exothermic process. This approach has the potential to allow formation of a range of binary, ternary, or higher-ordered compounds to be synthesized in the bulk, while avoiding the formation of many binary intermediates that may otherwise form in a diffusion-limited reaction.

Rational preparation of materials by design is a major goal of inorganic, solid-state, and materials chemists alike. Oftentimes, the use of nonmetallurgical reactions (e.g., chalcogenide fluxes, hydrothermal syntheses, and in this case solid-state metathesis) alters the thermodynamic driving force of the reaction and allows new, refractory, or otherwise energetically unfavorable materials to form under softer conditions. Taking this a step further, alteration of a metathesis reaction pathway can result in either the formation of the equilibrium marcasite polymorph (by stringent exclusion of air) or the kinetically controlled formation of the high-pressure pyrite polymorph of CuSe2 (by exposure to air). From analysis of the reaction coordinate with in situ synchrotron X-ray diffraction and pair distribution function analysis as well as differential scanning calorimetry, it is clear that the air-exposed reaction proceeds via slight, endothermic rearrangements of crystalline intermediates to form pyrite, which is attributed to partial solvation of the reaction from atmospheric humidity. In contrast, the air-free reaction proceeds via a significant exothermic process to form marcasite. Decoupling the formation of NaCl from the formation of CuSe2 enables kinetic control to be exercised over the resulting polymorph of these superconducting metal dichalcogenides.

Crystals of chromium tetraboride, a recently proposed candidate superhard material, have been grown for the first time to allow for a first structure refinement of the compound [orthorhombic, space group Immm (No. 71), a = 474.82(8) pm, b = 548.56(8) pm, and c = 287.17(4) pm, R value (all data) = 0.018]. The previously proposed structure model is confirmed, and accurate interatomic distances are presented for the first time. First-principles electronic structure calculations emphasize the unique framework of three-dimensionally linked B atoms that are tetrahedrally coordinated and carry a slightly negative charge. All B-B bonding is of the 2-center 2-electron type. CrB(4) is metallic with a pseudogap at the Fermi level.

Abstract. PbPdO 2 , a ternary compound containing the lone-pair active ion Pb 2+and the square-planar d8 Pd 2+ ion, has attracted recent interest because of the suggestion that its electronic structure, calculated within density functional theory using either the local density or the generalized gradient approximations, displays zerogap behavior. In light of the potential ease of doping magnetic ions in this structure, it has been suggested that the introduction of spin, in conjunction with zero band gap, can result in unusual magnetic ground states and unusual magnetotransport. It is known that most electronic structure calculations do not properly obtain a band gap even for the simple oxide PdO, and instead obtain a metal or a zero-gap semiconductor. Here we present density functional calculations employing a screened hybrid functional (HSE) which correctly obtain a band gap for the electronic structure of PdO. When employed to calculate the electronic ground state of PbPdO 2 , a band gap is again obtained, which is consistent both with the experimental data on this compound, as well as a consideration of valence states and of metal-oxygen connectivity in the crystal structure. We also present comparisons of the absolute positions (relative to the vacuum level) of the conduction band minima and the valence band maxima in α-PbO, PdO and PbPdO 2 , which suggest ease of p-type doping in PbPdO 2 that has been observed even in nominally pure materials.