T(c) maximum in solid solution of pyrite IrSe2-RhSe2 induced by destabilization of anion dimers

Platinum-Group Minerals in the Placer of the Kitoy River, East Sayan, Russia

The platinum-group minerals (PGM) in placer deposits provide important information on the types of their primary source rocks and ores and formation and alteration conditions. The article shows for the first time the results of a study of placer platinum mineralization found in the upper reaches of the Kitoy River (the southeastern part of the Eastern Sayan (SEPES)). Using modern methods of analysis (scanning electron microscopy), the authors studied the microtextural features of platinum-group minerals (PGM), their composition, texture, morphology and composition of microinclusions, rims, and other types of changes. The PGM are Os-Ir-Ru alloys with a pronounced ruthenium trend. Many of the Os-Ir-Ru grains have porous, fractured, or altered rims that contain secondary PGE sulfides, arsenides, sulfarsenides, Ir-Ni-Fe alloys, and rarer selenides, arsenoselenides, and tellurides of the PGE. The data obtained made it possible to identify the root sources of PGM in the placer and to make assumptions about the stages of transformation of primary igneous Os-Ir-Ru alloys from bedrock to placer. We assume that there are several stages of alteration of high-temperature Os-Ir-Ru alloys. The late magmatic stage is associated with the effect of fluid-saturated residual melt enriched with S, As. The post-magmatic hydrothermal stage (under conditions of changing reducing conditions to oxidative ones) is associated with the formation of telluro-selenides and oxide phases of PGE. The preservation of poorly rounded and unrounded PGM grains in the placer suggests a short transport from their primary source. The source of the platinum-group minerals from the Kitoy River placer is the rocks of the Southern ophiolite branch of SEPES and, in particular, the southern plate of the Ospa-Kitoy ophiolite complex, and primarily chromitites.

Pressure-Induced Collapse Transition in BaTi2Pn2O (Pn = As, Sb) with an Unusual Pn-Pn Bond Elongation

Making and breaking bonds in a solid-state compound greatly influences physical properties. A well-known playground for such bonding manipulation is the ThCr₂Si₂-type structure AT₂X₂, allowing a collapse transition where a X-X dimer forms by a chemical substitution or external stimuli. Here, we report a pressure-induced collapse transition in the structurally related BaTi₂Pn₂O (Pn = As, Sb) at a transition pressure P_c of ∼15 GPa. The Pn-Pn bond formation is related with Pn-p band filling, which is controlled by charge transfer from the Ti-3d band. At P_c, the Sb-Sb distance in BaTi₂Sb₂O shrinks due to bond formation, but interestingly, the Sb-Sb expands with increasing pressure above P_c. This expansion, which was not reported in ThCr₂Si₂-type compounds, may arise from heteroleptic coordination geometry around titanium, where a compression of the Ti-O bond plays a role. Electrical resistivity measurements of BaTi₂Sb₂O up to 55 GPa revealed an increasing trend of the superconducting transition temperature with pressure. This study presents structure motifs that allow flexible bonding manipulation and property control with heteroleptic coordination geometry.

Ir 5d-band derived superconductivity in LaIr3

The superconducting properties of rhombohedral LaIr₃ were examined using susceptibility, resistivity, heat capacity, and zero-field (ZF) and transverse-field (TF) muon spin relaxation and rotation ([Formula: see text]SR) measurements. The susceptibility and resistivity measurements confirm a superconducting transition below [Formula: see text] K. Two successive transitions are observed in the heat capacity data, one at [Formula: see text] K and a second at 1.2 K below [Formula: see text]. The heat capacity jump is [Formula: see text], which is lower than 1.43 expected for Bardeen-Cooper-Schrieffer (BCS) weak-coupling limit. TF-[Formula: see text]SR measurements reveal a fully gapped s-wave superconductivity with [Formula: see text], which is small compared to the BCS value of 3.56, suggesting weak-coupling superconductivity. The magnetic penetration depth, [Formula: see text], estimated from TF-[Formula: see text]SR gives [Formula: see text] nm, a superconducting carrier density [Formula: see text] carriers m^-3 and a carrier effective-mass enhancement factor [Formula: see text]. ZF-[Formula: see text]SR data show no evidence for any spontaneous magnetic fields below [Formula: see text], which demonstrates that time-reversal symmetry is preserved in the superconducting state of LaIr₃.

Anomalous Dome-like Superconductivity in RE2(Cu1-xNix)5As3O2 (RE = La, Pr, Nd)

A significant manifestation of interplay of superconductivity and charge density wave, spin density wave, or magnetism is a dome-like superconducting critical temperature (Tc) in cuprate, iron-based, and heavy Fermion superconductors. Pesudogap, quantum critical point, and strange metals emerge in different doping ranges. Exploring dome-like Tc in new superconductors is of interest to detect emergent effects. Here we report the superconductivity in a new layered Cu-based compound RE2Cu5As3O2 (RE = La, Pr, Nd), in which the Tc exhibits dome-like variation with a maximum Tc of 2.5, 1.2, and 1.0 K with substitution of Cu by large amount of Ni ions. Simultaneously, the structural parameters like As-As bond length and c/a ratio exhibit unusual variations as the Ni-doping level goes through the optimal value. The robustness of superconductivity, up to 60% of Ni doping, reveals the unexpected impurity effect on inducing and enhancing superconductivity in these novel layered materials.

Structure and Transport Properties in Itinerant Antiferromagnet RE2(Ni1- xCu x)5As3O2 (RE = Ce, Sm)

We report the crystal structure and physical properties of two Ni₅As₃-based compounds RE₂Ni₅As₃O₂ (RE = Ce, Sm). The former exhibits structural phase transition from tetragonal (space group I4/ mmm, 139) to orthorhombic (space group Immm, 71) symmetry at 230 K, while the latter undergoes a charge-density-wave-like structural distortion with abrupt change of Ni-As bond length. Both compounds show antiferromagnetic transitions due to RE³⁺ ions ordering at 4.4 and 3.4 K, accompanying with the large enhancement of Sommerfeld coefficients comparing to the nonmagnetic La analogue. Although the Cu substitution for Ni induces structural anomalies and suppression of structural transition like the behaviors in La/Pr/Nd analogues, the superconductivity is not observed in both Cu-doped RE₂Ni₅As₃O₂ (RE = Ce, Sm) above 0.25 K. Our structural refinements reveal that the lacking of superconductivity in RE₂(Ni_{1- x}Cu _x)₅As₃O₂ might relate to the anomalous increase of As height, h₁.

Exploration of new superconductors and functional materials, and fabrication of superconducting tapes and wires of iron pnictides

This review shows the highlights of a 4-year-long research project supported by the Japanese Government to explore new superconducting materials and relevant functional materials. The project found several tens of new superconductors by examining ∼1000 materials, each of which was chosen by Japanese experts with a background in solid state chemistry. This review summarizes the major achievements of the project in newly found superconducting materials, and the fabrication wires and tapes of iron-based superconductors; it incorporates a list of ∼700 unsuccessful materials examined for superconductivity in the project. In addition, described are new functional materials and functionalities discovered during the project.

Layered compounds BaM2Ge4Ch6 (M = Rh, Ir and Ch = S, Se) with pyrite-type building blocks and Ge-Ch heteromolecule-like anions

The structures and chemical features of layered compounds BaM2Ge4Ch6 (M = Rh, Ir; Ch = S, Se) synthesized by high-pressure and high-temperature methods have been systematically studied. These compounds crystallize in an orthorhombic phase with space group Pbca (No. 61). These compounds have the remarkable structural feature of M-Ge-Ch pyrite-type building units, stacking with Ba-Ch layers alternatively along the c axis. It is very rare and novel that pyrite-type subunits are the building blocks in layered compounds. Theoretical calculations and experimental results indicate that there are strongly polarized covalent bonds between Ge and Ch atoms, forming heteromolecule-like anions in these compounds. Moreover, Ge atoms in this structure exhibit an unusual valence state (∼+1) due to the tetrahedral coordination environment of Ge atoms along with M and Ch atoms simultaneously.

Superconducting fiber with transition temperature up to 7.43 K in Nb2PdxS5-δ (0.6 < x <1)

Wiring systems powered by highly efficient superconductors have long been a dream of scientists, but researchers have faced practical challenges such as finding flexible materials. Here we report superconductivity in Nb2PdxS5-δ fibers with transition temperature up to 7.43 K, which have typical diameters of 0.3-3 μm. Superconductivity occurs in a wide range of Pd (0.6 < x <1) and S (0 < δ <0.61) contents, suggesting that the superconductivity in this system is very robust. Long fibers with suitable size provide a new route to high-power transmission cables and electronic devices.