High-temperature synthesis, single-crystal X-ray and neutron powder diffraction, and materials properties of Sr3Ln10Si18Al12O18N36 (Ln = Ce, Pr, Nd)

The novel oxonitridoaluminosilicates (sialons) Sr3Ln10Si18Al12O18N36 (Ln = Ce, Pr, Nd) were obtained by the reaction of the respective lanthanide metals with Si(NH)2, SrCO3, and AlN using a radiofrequency furnace at temperatures between 1550–1650°C. The crystal structures of the isotypic sialons were determined by single-crystal X-ray investigations (Sr3Ce10Si18Al12O18N36: I3m, Z = 2, a = 1338.2(2) pm, R1 = 0.0333; Sr3Pr10Si18Al12O18N36: a = 1334.54(6) pm, R1 = 0.0296; Sr3Nd10Si18Al12O18N36: a = 1332.85(6) pm, R1 = 0.0271) and in the case of Sr3Pr10Si18Al12O18N36 with powder neutron diffraction as well. The three-dimensional sialon network is built up by SiON3, SiN4, and AlON3 tetrahedra. Besides the bridging O and N atoms of the sialon network there are isolated O2− which are tetrahedrally coordinated by Sr and Ln. The crystallographic differentiation of Si/Al and O/N seemed to be possible by a careful evaluation of the single-crystal X-ray diffraction data combined with lattice energy calculations using the MAPLE concept (Madelung Part of Lattice Energy). In the case of Sr3Pr10Si18Al12O18N36 the differentiation of O and N and the proposed ordering was completely confirmed by powder neutron diffraction

Synthesis and structure of pseudo- three dimensional hybrid iodobismuthate semiconductors

Semiconducting hybrid bismuth iodides, templated on piperizinium cations and their methylated derivatives, have pseudo three-dimensional connectivity reminiscent of the perovskite structure.</p

Lattice dynamics and vibrational spectra of the orthorhombic, tetragonal and cubic phases of methylammonium lead iodide

The hybrid halide perovskite CH3NH3PbI3 exhibits a complex structural behaviour, with successive transitions between orthorhombic, tetragonal and cubic polymorphs at ca. 165 K and 327 K. Herein we report first-principles lattice dynamics (phonon spectrum) for each phase of CH3NH3PbI3. The equilibrium structures compare well to solutions of temperature-dependent powder neutron diffraction. By following the normal modes we calculate infrared and Raman intensities of the vibrations, and compare them to the measurement of a single crystal where the Raman laser is controlled to avoid degradation of the sample. Despite a clear separation in energy between low frequency modes associated with the inorganic PbI3 network and high-frequency modes of the organic CH3NH3+ cation, significant coupling between them is found, which emphasises the interplay between molecular orientation and the corner-sharing octahedral networks in the structural transformations. Soft modes are found at the boundary of the Brillouin zone of the cubic phase, consistent with displacive instabilities and anharmonicity involving tilting of the PbI6 octahedra around room temperature.Comment: 9 pages, 4 figure

High-throughput synthesis and characterization of BiMoVOX materials

The high throughput synthesis and characterization of a particular family of ceramic materials, bismuth molybdenum vanadium oxides (BiMoVOX), suitable as inorganic yellow pigments and low temperature oxidation catalysts, is described. Samples, synthesized by calcination and peroxo sol-gel methods, are characterized by X-ray powder diffraction, UV-visible and XAFS spectroscopy. A combined high-throughput XRD/XAFS study of a 54 samples array, with simultaneous refinement of data of both techniques, has been performed. Molybdenum doping of bismuth vanadate results in a phase transition from monoclinic BiV04 to tetragonal Bi(V,Mo)04, both of scheelite type. Both central metals, V5+ and Mo6+, remain in a tetrahedral coordination. UV/visible spectroscopy identifies a linear blue shift as a function of Mo6+ amount

Phase Behavior and Substitution Limit of Mixed Cesium-Formamidinium Lead TriIodide Perovskites

The mixed cation lead iodide perovskite photovoltaics show improved stability following site substitution of cesium ions (Cs+) onto the formamidinium cation sites (FA+) of (CH(NH2)2PbI3 (FAPbI3) and increased resistance to formation of the undesirable ∂-phase. The structural phase behavior of Cs0.1FA0.9PbI3 has been investigated by neutron powder diffraction (NPD), complemented by single crystal and power X-ray diffraction and photoluminescence spectroscopy. The Cs-substitution limit has been determined to be less than 15%, and the cubic α-phase, Cs0.1FA0.9PbI3, is shown to be synthesizable in bulk and stable at 300 K. On cooling the cubic Cs0.1FA0.9PbI3, a slow, second-order cubic to tetragonal transition is observed close to 290 K, with variable temperature NPD indicating the presence of the tetragonal β-phase, adopting the space group P4/mbm between 290 and 180 K. An orthorhombic phase or twinned tetragonal phase is formed below 180 K, and the temperature for further transition to a disordered state is lowered to 125 K compared to that seen in phase pure α-FAPbI3 (140 K). These results demonstrate the importance of understanding the effect of cation site substitution on structure–property relationships in perovskite materials

Experimental and theoretical optical properties of methylammonium lead halide perovskites

The optical constants from the ellipsometry of single crystals of CH3NH3PbX3(X = I, Br, Cl) are interpreted with high levelab initioQSGW calculations.</p

Visible light promoted photocatalytic water oxidation:proton and electron collection: via a reversible redox dye mediator

A quinone analogue as reversible electron and proton collector in visible light promoted water oxidations was investigated. Reagents were incorporated into microporous silica with surface absorbed cobalt catalyst. Reversible storage molecules are an important step towards solar fuels.</p

Probing hydrogen positions in hydrous compounds:information from parametric neutron powder diffraction studies

We demonstrate the extent to which modern detector technology, coupled with a high flux constant wavelength neutron source, can be used to obtain high quality diffraction data from short data collections, allowing the refinement of the full structures (including hydrogen positions) of hydrous compounds from in situ neutron powder diffraction measurements. The in situ thermodiffractometry and controlled humidity studies reported here reveal that important information on the reorientations of structural water molecules with changing conditions can be easily extracted, providing insight into the effects of hydrogen bonding on bulk physical properties. Using crystalline BaCl2 center dot 2H(2)O as an example system, we analyse the structural changes in the compound and its dehydration intermediates with changing temperature and humidity levels to demonstrate the quality of the dynamic structural information on the hydrogen atoms and associated hydrogen bonding that can be obtained without resorting to sample deuteration

Visible light promoted photocatalytic water oxidation:effect of fluctuating light intensity upon reaction efficiency

Repeat cyclic fluctuating intensity illumination can significantly improve reaction efficiencies of water oxidations by optimizing the photocyclic sequence and minimizing light sensitizer decomposition.</p