The structural stability of MgH2 has been studied up to 16 GPa using a high-pressure synchrotron x-ray diffraction technique. Several pressure-induced phase transitions have been identified in this pressure range. Owing to the close structural similarity between the alpha and gamma modifications the high-pressure gamma form can be stabilized as a metastable phase after pressure release. The experimentally observed structural transition sequence and the volume changes at the transition points as well as bulk modulii are found to be in good agreement with theoretically calculated data. The bonding nature of MgH2 is analyzed with the help of charge-density, charge-transfer, electron-localization-function, and Mulliken-population analyses which clearly show that all polymorphs of MgH2 are to be classified as ionic materials with Mg and H in nearly 2+ and 1- states, respectively.

The crystal structure of Ni13Sn8 P-3 was elucidated from High Resolution Electron Microscopy Images. It was found to be a superstructure of the B8-type (NiAs-type) structure with Sri and P atoms ordered at the hexagonally closepacked array and Ni atoms in all octahedral and in two out of every eleven trigonal bipyramidal sites. The structure motif within a NiSn B8-type matrix comprises triangles of P atoms with two of the three edges capped by Ni atoms in trigonal bipyramidal sites. This motif is repeated along the [0 (1) over bar1](B8) zone axis so that the structure can be envisaged as pairs of face-sharing Ni centered Edshammar polyhedra corner-connected along [0 (1) over bar1](B8). The reciprocal lattice (H) can be described as H = G + mq(1) + nq(2) (where G refers to the Bragg reflections of the underlying B8-type structure, q(1) = 1/11 [11 (2) over bar1](B8), q(2) = 1/22 [(6) over bar 515](B8) and m and n are integers. The resultant triclinic (P (1) over bar) unit cell parameters are a = 6.456 Angstrom, b = 21.291 Angstrom, c = 13.247 Angstrom, alpha = 81.052degrees, beta = 56.260degrees and gamma = 68.221degrees. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Selected-area electron diffraction revealed that Ni10Sn5P3 forms a superstructure of the NiAs-type structure. All observed reflections could be fully indexed as H=G+mq, where G represents the reflections of the underlying hexagonal B8-type average structure, m is an integer and q=18[3122]*. The resulting space group is P1 (Z=2). The crystal structure was refined using single-crystal X-ray diffraction methods on a twinned specimen (1651 observed unique reflection, Rw obs=0.0391). The superstructure reflections are caused by ordering of Sn and P atoms on the hcp array coupled to Ni ordering in 14 of the trigonal bipyramidal sites. The unit-cell parameters refined from powder X-ray diffraction data are a=6.419(2) Å, b=8.322(3) Å, c=10.278(3) Å, α=73.32(4)°, β=84.41(3)°, γ=82.71(2)°, V=520.60(5) Å3. High-resolution electron microscopy images revealed a well-ordered material although macroscopic crystals are twinned.

Bi nanorods and NiBi particles were prepared using a simple hydrothermal reduction method at moderate temperatures of 150 °C. Transmission electron microscopy (TEM) reveals pure Bi nanorods with diameters of about 50 nm and superconducting NiBi particles. The magnetic susceptibility (χ) of the superconducting NiBi was measured as a function of temperature at 10 Oe.

Epitaxial intergrowths of Fe6Ge5andB8-type Fe1+xGe was investigated by means of electron diffraction. A crystal structure description of Fe6Ge5in terms ofB8- andB1-type structures was established; 4/5 of the Ge atoms in Fe6Ge5can be described with one-octahedron wide slabs of hexagonal close-packed Ge atoms with all octahedral sites and 1/2 of the trigonal bipyramidal sites therein filled with Fe atoms (B8). Additionally, all Ge atoms can be described by a two-octahedra wide slab of cubic close-packed Ge atoms with 4/6 of the octahedral sites filled with Fe atoms and 1/6 of the octahedral sites filled withtwoFe atoms, one in each square pyramid (B1). At the surface interconnecting these slabs, octahedra from theB8 andB1 slabs share faces and the trigonal bipyramid from the hcp array and two edge-sharing tetrahedra from the ccp array are merged to form a pentagonal bipyramid.

Electron diffraction is used to investigate Sn/P and interstitial Ni atom ordering in the apparent wide range, non-stoichiometric Ni1+mSn1−xPxternary B8-type solid solution. Two complex modulated structures are found to exist in a limited area of the solid solubility range, described by compositions around Ni1.1Sn0.7P0.3. This region of the high temperature Ni1+mSn1−xPx, B8-type phase field had previously been found to separate out as an isolated B8 type phase region at low temperatures. A complex, long range ordered triclinic superstructure phase is found for specimens quenched from lower temperatures and a plausible structural model, based on ordering of NiP3Sn2trigonal bipyramidal clusters, proposed. The underlying B8 subcell remains metrically hexagonal so that there are at least 12 distinct twin variants whose B8 sublattice reflections overlap exactly. The diffraction patterns characteristic of specimens quenched from higher temperatures are compatible with a multiply twinned microdomain model.

Ordered Mn3Sn2 appears as a distinct low-temperature phase in the binary MnSn system. On heating it decomposes peritectoidally around 813 K into the grossly non-stoichiometric Mn2−xSn phase and MnSn2. Phase relations are described for Mn3Sn2 and Mn2−xSn on the basis of samples where great care has been taken during synthesis to minimize inhomogeneity owing to manganese evaporation and/or transportation. Mn2−xSn exists between 753 and 1157 K. The non-stoichiometry of Mn2−xSn is strongly temperature dependent. At 1073 K, the homogeneity range is 0.18≤x≤0.23, whereas at 873 K 0.28≤x≤0.34. The crystal structure of Mn2−xSn is of the partly filled-up NiAs-type. The crystal structure of the ordered Mn3Sn2 phase was solved on the basis of powder X-ray and neutron diffraction data. Mn3Sn2 is isostructural to Co3Sn2 and Ni3Sn2. Phase transformation and structural relationships are discussed.

The 'new' phase V15Sb18 has been synthesized as polycrystalline powder and as single crystals by means of chemical transport reactions. V15Sb18 is shown to be the correct formula for the phase described as V5Sb4 in the literature, and most probably there exists no phase with a Ti5Te4-type crystal structure as assumed earlier. V15Sb18 crystallizes in space group P4/nmm with a = 958.66 +/- 0.05 and c = 704.74 +/- 0.05 pm. Its crystal structure was solved on the basis of single-crystal X-ray diffraction data (R = 0.030). One of the vanadium sites (in position 2c) is half-filled. This special feature was verified for another single crystal which was grown without iodine as transporting agent. According to data for powder samples with different nominal compositions, the phase has no major range of homogeneity. The phase exhibits weak, almost temperature-independent paramagnetism. At high temperatures, T = 1205 +/- 10 K, V15Sb18 decomposes peritectoidally into VSb2 and V1.4Sb (NiAs-type). The atomic arrangement shows structural elements typical both for VSb2 and for V3Sb (CuAl2-type and Cr3Si-type, respectively). Two types of columns of coordination polyhedra running along [001] are identified, columns of V tetrahedra connected by Sb atoms, and columns of distorted, square antiprismatic V-Sb units ([V2Sb8](n) chains). The relationship between the antiprismatic building units of V15Sb18, VSb2 and VS4 is described. The metal-metal bonding is extensive. The V-4 tetrahedra are connected by 'single' V atoms forming a two-dimensional network of V-V close contacts (268-295 pm).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The conditions for the existence of an Ni1+mSn1-xPx solid solution phase with a partly filled NiAs-type structure are described. The phase has a large homogeneity region at high temperatures which includes Ni3Sn2. At room temperature, the phase exists only for a small composition range (in x, m). Metastable one-phase samples were obtained on quenching. Single-crystal X-ray and powder neutron diffraction data provide weak indications for deviations from the ideal structure. A tendency towards formation of NiP3Sn2 clusters at the trigonal bipyramidal sites is proposed. Thermal expansion data are presented for the quenched, metastable NiAs-type phase, and transformations into stable products are described. The phase exhibits Pauli paramagnetism.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Chloroquine diphosphate was investigated by differential scanning calorimetry, thermogravimetric analysis, infrared spectroscopy, X-ray powder diffraction and by scanning electron microscopy for the indication of differences between anhydrous and hydrous polymorphs. The experiments clearly showed that the transition of anhydrous chloroquine diphosphate into hydrated compounds is possible by storing the drug at high relative humidity. Compression of the raw material did result in the formation of a new polymorph. This emphasizes the necessity for standardization of the manufacturing process of chloroquine diphosphate as well as a closer characterization of the solid drug as a part of the quality control.

The Ti1-xNbxS2 phase crystallizing with the CdI2 (1T) type of structure has been investigated. At 1000-degrees-C and with a sulphur pressure of 6-8 atm the range of homogeneity is given by 0 < x < 0.98. The structural z parameter increases from the previously known value of 0.2501 in TiS2, through 0.2559 for x = 0.50 to 0.2611 for x = 0.95. The trigonal distortion of the metallic coordination polyhedron increases strongly and the interlayer distance of the structure decreases as titanium is substituted by the electron-richer niobium.

Re-examination of the crystal structure of ZrTe3 by single-crystal methods shows that ZrTe3, contrary to earlier reports, takes the type A structure for MX3 compounds. Repeated syntheses of a large number of crystals, using various conditions in the transport reactions, gave only type A crystals. The powder X-ray and neutron diffraction patterns are only compatible with a type A bulk material. Two other representatives of the type B class of MX3 compounds were studied, but in less detail. However, the present results clearly show that their structures are also of type A. No indication for a type B material was found for any of these compounds. It is recommended that property measurements of low-dimensional MX3 compounds are accompanied by structural characterization in order to ascertain the type of the studied material. A list of Bragg reflections (powder X-ray diffraction data), particularly suited for differentiating between type A and type B materials, is provided.

Complete solid miscibility is found for Ni1−tRhtBi3 (0.00 ⩽ t ⩽ 1.00). The crystal structure is of the NiBi3 type and the positional parameters are found to vary insignificantly with composition t. The decomposition temperature decreases with increasing rhodium content from 753 ± 10 K for NiBi3 to 445 ± 10 K for RhBi3.

AbstractThe homogeneity range of the title phase is strongly temp.‐dependent.

The penta-, tri- and ditellurides of zirconium and hafnium easily take up oxygen and become partly oxidized at and below room temperature. Complete oxidation of these phases to (amorphous) ZrO2 or HfO2 and (crystalline) Te is attained at some 320 to 500K (depending on compound, sample characteristics and experimental conditions) provided sufficient amounts of oxygen are available. Explanations for the different anomalies in ZrTe5 are advanced as adsorbed/absorbed oxygen in the voids of the structure, partial oxidation, partial destruction of the TeIII-TeIII zig-zag chains in the structure and decomposition to the corresponding tritelluride and Te.

AbstractThe Title compound (prepared directly from the elements at 900‐1000 Kand crystallized from tin melts) crystallizes in the space group Pnma with Z=4.