γ-phase evolution in aged Co–Ni–Ga shape memory alloy

A synchrotron X-ray diffraction study of high-temperature (HT) shape memory alloy 49Co–21Ni–30Ga (in at. pct.) was performed. The volume fraction, cell parameter and temperature evolution of the different secondary phases were analyzed. This study reports reliable experimental data on these parameters to be used as a future reference to adjust the composition of the material.

Production of Thin PbxSn1–xTe Films by “Hot Wall” Method for Creating IR-Photodetectors

Alloys of lead and tin telluride (PbxSn1–xTe) are materials with good thermoelectric properties, as well as semiconductors that can be used as long-wave infrared detectors. Polycrystalline telluride of PbxSn1–xTe (0.05 £ x £ 0.80) alloys has been synthesized by direct fusion technique. Thin films of these materials have been obtained by the hot wall method depositing Сorning 7059 on glass substrates at Tsub = (200–350) oC and vacuum of about 10–5 Torr. The microstructure of the films has been investigated by XRD, SEM and EDX methods. The X-ray spectra of thin films have been in satisfactorily agreement with the spectra of the powder target and indicated the absence of binary phases. The films have shown a natural cubic crystalline structure. While increasing the lead content, the unit cell parameter of the crystal also increases. The established linear relationship between the unit cell parameter and the elemental composition corresponds to Vegard's law. The SEM analysis has shown that the films are polycrystalline, have a columnar structure, are tightly packed and have good mechanical adhesion. The grain size depends on the chemical composition and temperature of the substrate. The electrical measurements have shown that the grown films are non-degenerate semiconductors of p-type conductivity. The conductivity of the films was in the range of σ = (3 × 101)–(1 × 104) Ω–1×cm–1. An increase of lead concentration leads to a decrease in electrical conductivity. Hall mobility in the grown thin films increases in the range of changes in the lead content from ~10 to ~23 at. %, and decreases with a further increase to ~33 at. %. At the same time, the strongest dependence of the decrease in mobility on an increase in temperature increase is observed for films with a high lead content and is explained by the predominant scattering of charge carriers by vibrations of the crystal lattice. For a sample with an average lead concentration, an alternative effect of two scattering mechanisms is observed in the temperature dependence of the mobility: by impurity ions and by phonons.

Crystal Structure of an Anisotropic Pyrope Garnet That Contains Two Cubic Phases

The crystal structure of two different samples of pyrope garnet, ideally Mg3Al2Si3O12, from South Africa was refined using the Rietveld method, space group Ia3¯d, and monochromatic synchrotron high-resolution powder X-ray diffraction (HRPXRD) data. Sample 1 from Wesselton Mine is a single cubic phase and is optically isotropic. Electron-probe microanalysis (EPMA) provided an average composition {Mg2.30Fe2+0.26Ca0.42Mn2+0.02}∑3[Al1.53Fe3+0.06Cr3+0.40Ti4+0.01Fe2+0.01]∑2Si3O12, which contains a significant amount of Cr cations. The unit-cell parameter (Å) and bond distances (Å) are a = 11.56197(1) Å, average <Mg-O> = 2.2985, Al-O = 1.9101(4), and Si-O = 1.6343(3) Å. Sample 2 from De Beers Diamond Mine has an average composition {Mg2.33Fe2+0.33Ca0.33Mn2+0.01}∑3[Al1.73Fe3+0.12Cr3+0.06Ti4+0.05Fe2+0.05]∑2Si3O12 and is a fine-scale intergrowth of two cubic phases. The weight percentage, unit-cell parameter (Å), and bond distances (Å) for phase 2a are 62.2(1)%, a = 11.56185(1) Å, average <Mg-O> = 2.3006, Al-O = 1.9080(4), Si-O = 1.6334(4) Å. The corresponding values for phase 2b are 37.8(1)%, a = 11.53896(1) Å, average <Mg-O> = 2.2954, Al-O = 1.9020(6), Si-O = 1.6334(6) Å. The two cubic phases in sample 2 cause the crystal to be optically anisotropic because of strain induce birefringence. The unit-cell parameter and bond distances for sample 1 are similar to those in phase 2a.

A self-consistent approach to describe unit-cell-parameter and volume variations with pressure and temperature

A method for the self-consistent description of the large variations of unit-cell parameters of crystals with pressure and temperature is presented. It employs linearized versions of equations of state (EoSs) together with constraints to ensure internal consistency. The use of polynomial functions to describe the variation of the unit-cell angles in monoclinic and triclinic crystals is compared with the method of deriving them from linearized EoSs for d spacings. The methods have been implemented in the CrysFML Fortran subroutine library. The unit-cell parameters and the compressibility and thermal expansion tensors of crystals can be calculated from the linearized EoSs in an internally consistent manner in a new utility in the EosFit7c program, which is available as freeware at http://www.rossangel.net.

Nanobody-aided crystallization of the transcription regulator PaaR2 from Escherichia coli O157:H7

paaR2–paaA2–parE2 is a three-component toxin–antitoxin module found in prophage CP-993P of Escherichia coli O157:H7. Transcription regulation of this module occurs via the 123-amino-acid regulator PaaR2, which forms a large oligomeric structure. Despite appearing to be well folded, PaaR2 withstands crystallization, as does its N-terminal DNA-binding domain. Native mass spectrometry was used to screen for nanobodies that form a unique complex and stabilize the octameric structure of PaaR2. One such nanobody, Nb33, allowed crystallization of the protein. The resulting crystals belong to space group F432, with unit-cell parameter a = 317 Å, diffract to 4.0 Å resolution and are likely to contain four PaaR2 monomers and four nanobody monomers in the asymmetric unit. Crystals of two truncates containing the N-terminal helix–turn–helix domain also interact with Nb33, and the corresponding co-crystals diffracted to 1.6 and 1.75 Å resolution.

Comparison of the temperature- and pressure-dependent behavior of the crystal structure of CrAs

The crystal structure of CrAs was investigated using synchrotron X-ray single-crystal diffraction for separate dependences on temperature (30–400 K) and on pressure (0–9.46 GPa). The isosymmetrical magnetostructural phase transition at T N = 267 K can induce a change in the microstructure by twinning due to a crossing of the orthohexagonal setting of the unit-cell parameter ratio c/b. Within the crystal structure, one particular Cr–Cr distance exhibits anomalous behavior in that it is nearly unaffected by temperature and pressure in the paramagnetic phase, which is stable above 267 K and at high pressures. The distinction of this shortest Cr–Cr distance might be of importance for the superconducting properties of CrAs.

Coarse-crystalline pyrite of the Central Timan

The results of mineralogical, geochemical, X-ray, isotopic and spectroscopic studies of coarse-crystalline pyrite (Kyvvozh Formation, Dimtem’el Creek, Central Timan) are presented. Pyrite is characterized by cubic habit and zonal Co distribution. It contains galena, thorite, zircon, monazite, rutile, chlorite, muscovite, quartz, albite, apatite and calcite inclusions. The unit cell parameter of pyrite vary from 5.4137 ± 0.0002 to 5.4187 ± 0.0010 A and correspond to an ideal pyrite. The sulfur isotopic composition of coarse-crystalline pyrite of 15.8‰ indicates its formation as a result of sulfate reduction during epigenesis.