Ferrotorryweiserite, Rh5Fe10S16, a New Mineral Species from the Sisim Placer Zone, Eastern Sayans, Russia, and the Torryweiserite–Ferrotorryweiserite Series

Ferrotorryweiserite, Rh5Fe10S16, occurs as small grains (≤20 µm) among droplet-like inclusions (up to 50 μm in diameter) of platinum-group minerals (PGM), in association with oberthürite or Rh-bearing pentlandite, laurite, and a Pt-Pd-Fe alloy (likely isoferroplatinum and Fe-Pd-enriched platinum), hosted by placer grains of Os-Ir alloy (≤0.5 mm) in the River Ko deposit. The latter is a part of the Sisim placer zone, which is likely derived from ultramafic units of the Lysanskiy layered complex, southern Krasnoyarskiy kray, Russia. The mineral is opaque, gray to brownish gray in reflected light, very weakly bireflectant, not pleochroic to weakly pleochroic (grayish to light brown tints), and weakly anisotropic. The calculated density is 5.93 g·cm–3. Mean results (and ranges) of four WDS analyses are: Ir 18.68 (15.55–21.96), Rh 18.34 (16.32–20.32), Pt 0.64 (0.19–1.14), Ru 0.03 (0.00–0.13), Os 0.07 (0.02–0.17), Fe 14.14 (13.63–14.64), Ni 13.63 (12.58–14.66), Cu 4.97 (3.42–6.41), Co 0.09 (0.07–0.11), S 29.06 (28.48–29.44), and total 99.66 wt. %. They correspond to the following formula calculated for a total of 31 atoms per formula unit: (Rh3.16Ir1.72Pt0.06Ru0.01Os0.01)Σ4.95(Fe4.48Ni4.11Cu1.38Co0.03)Σ10.00S16.05. The results of synchrotron micro-Laue diffraction studies indicate that ferrotorryweiserite is trigonal; its probable space group is Rm (#166) based on its Ni-analog, torryweiserite. The unit-cell parameters refined from 177 reflections are a = 7.069 (2) Å, c = 34.286 (11) Å, V = 1484 (1) Å3, and Z = 3. The c:a ratio is 4.8502. The strongest eight peaks in the X-ray diffraction pattern derived from results of micro-Laue diffraction study [d in Å(hkil)(I)] are 2.7950 (205) (100); 5.7143 (0006) (60); 1.7671 (220) (44.4); 3.0486 (201) (39.4); 5.7650 (102) (38.6); 2.5956 (207) (37.8); 3.0058 (116) (36.5); and 1.5029 (412) (35.3). Ferrotorryweiserite and the associated PGM crystallized from microvolumes of residual melt at late stages of crystallization of grains of Os- and Ir-dominant alloys occurred in lode zones of chromitites of the Lysanskiy layered complex. In a particular case, the residual melt is disposed peripherally around a core containing a disequilibrium association of magnesian olivine (Fo72.9–75.6) and albite (Ab81.6–86.4), with the development of skeletal crystals of titaniferous augite: Wo40.8–43.2En26.5–29.3Fs20.3–22.6Aeg6.9–9.5 (2.82–3.12 wt. % TiO2). Ferrotorryweiserite represents the Fe-dominant analog of torryweiserite. We also report occurrences of ferrotorryweiserite in the Marathon deposit, Coldwell Complex, Ontario, Canada, and infer the existence of the torryweiserite–ferrotorryweiserite solid solution in other deposits and complexes.

Laue diffraction of X-ray microbeams by multilayers

Laue diffraction theory of X-ray microbeams in multilayers (MLs) is developed. The solution for calculating X-ray reciprocal space maps is obtained. The pendulum (Pendellösung) effect for perfect and imperfect MLs is shown. The numerical simulation of Laue diffraction in Mo/Si multilayers with boundary conditions in the case of geometrical optics and the Fresnel approximation is carried out. It is shown that for X-ray microbeams one should to take into account the diffraction of X-ray waves at the edges of slits (collimators) of the diffraction scheme.

X-ray Laue diffraction by sectioned multilayers. I. Pendellösung effect and rocking curves

Using the Takagi–Taupin equations, X-ray Laue dynamical diffraction in flat and wedge multilayers is theoretically considered. Recurrence relations are obtained that describe Laue diffraction in structures that are inhomogeneous in depth. The influence of sectioned depth, imperfections and non-uniform distribution of the multilayer period on the Pendellösung effect and rocking curves is studied. Numerical simulation of Laue diffraction in multilayer structures W/Si and Mo/Si is carried out. It is shown that the determination of sectioned depths based on the period of the interference fringes of the experimental rocking curves of synchrotron radiation is not always correct.

Laue X-ray diffraction studies of the structural perfection of Al-doped thermomigration channels in silicon

Si(111) wafers patterned with an array of vertical 100 µm-wide Al-doped (1 × 1019 cm−3) p-channels extending through the whole wafer were studied by X-ray Laue diffraction techniques. The X-ray techniques included projection topography, and measurement of rocking curves and cross sections in the vicinity of the 02\overline 2 reciprocal space node in the double- and triple-crystal geometry, respectively. The channels are uniform along the depth of the wafer, and their structural perfection is comparable to that of the silicon matrix between the channels. Simulation of the rocking curves was performed using the methods of the dynamical theory of X-ray diffraction. The rocking-curve calculations both taking into account and neglecting the effect of the instrumental function were carried out using the Takagi–Taupin equations. The calculated angular dependences of intensities of both diffracted and transmitted X-rays correspond well to the experimentally obtained rocking curves and demonstrate their high sensitivity to the structural distortions in the channel. An unambiguous reconstruction of strain and structural distortions in the Si(Al) channel using the Laue diffraction data requires further development of the theoretical model.

On ab initio indexing of Laue diffraction patterns

The Laue method allows for fast pattern acquisition, but its use in structural studies is limited by the complexity of data processing. In particular, automatic ab initio indexing of Laue patterns is not trivial. This paper describes measures improving the effectiveness of indexing software. The first such measure is to adjust the positions of Laue spots on the basis of a mesh of lines fitted in a consistent way. Two other modifications enlarge the set of cells tested as potential primitive lattice cells. The last modification concerns eliminating solutions representing superlattices of the true reciprocal lattice. The impact of using these schemes on the chances of obtaining correct indexing solutions is illustrated. The described procedures can be implemented to create fully automatic software for ab initio indexing of Laue patterns.

Submicronic Laue diffraction to determine in-depth strain in very closely matched complex HgCdTe/CdZnTe heterostructures with a 10−5 resolution

Cross-sectional submicronic Laue diffraction has been successfully applied to HgCdTe/CdZnTe heterostructures to provide accurate strain profiles from substrate to surface. Combined with chemical-sensitive techniques, this approach allows correlation of lattice-mismatch, interface compositional gradient and strain while isolating specific layer contributions which would otherwise be averaged using conventional X-ray diffraction. The submicronic spatial resolution allowed by the synchrotron white beam size is particularly suited to complex infrared detector designed structures such as dual-color detectors. The extreme strain resolution of 10−5 required for the very low lattice-mismatch system HgCdTe/CdZnTe is demonstrated.

Twinning in MAPbI3 at room temperature uncovered through Laue neutron diffraction

The crystal structure of MAPbI3, the signature compound of the hybrid halide perovskites, at room temperature has been a reason for debate and confusion in the past. Part of this confusion may be due to twinning as the material bears a phase transition just above room temperature, which follows a direct group–subgroup relationship and is prone to twinning. Using neutron Laue diffraction, we illustrate the nature of twinning in the room temperature structure of MAPbI3 and explain its origins from a group-theoretical point-of-view.