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In this work, the superconducting properties of FeSe1−xSx with 0 ≤ x ≤ 0.5 were studied. With S doping, Tc is enhanced and shows a dome shape in the studied composition range. XRD measurements demonstrate that S substituting Se sites introduces positive chemical pressure, which can suppress the orbital ordering, manifesting as the decrease of Ts. Hall measurements demonstrate that S doping can effectively tune the charge carriers and make hole-type carriers predominant. However, no maxing Tc is obtained as Ts vanishes in FeSe0.7S0.3, indicating the nematic order has no universal influence on the superconductivity of FeSe system.

Y2O3-doped tungsten (W–Y2O3) composite powders prepared by a traditional chemical co-precipitation method possess obvious bimodal distribution in size, which would deteriorate their sintering properties. The bimodal distribution can be effectively eliminated by an improved chemical co-precipitation method, in which the cationic surfactant cetyltrimethylammonium bromide (CTAB) was innovatively employed. The reduced powders with excellent uniformity have an average grain size of only ~ 31.5 nm. It is noteworthy that Y2O3 particles would fuse and grow with the growth of W grains during subsequent spark plasma sintering (SPS) process, which was rarely reported in relevant literature before. On top of that, phase interfaces of sintered W–Y2O3 alloys were systematically analyzed. Compared to the intracrystalline oxygen content, the oxygen content at W/Y2O3 phase boundaries is relatively higher. It can be found that the (110) crystal planes of W form coherent, semi-coherent, and non-coherent interfaces with different crystal planes of Y2O3. The weak interfacial bonding strength between W and Y2O3 phases results from relatively more oxygen impurities as well as more semi-coherent/non-coherent interfaces at phase boundaries compared with the inner W grains.

We reported the enhanced superconducting performance of Nb doped FeSe prepared by solid-state sintering. With the increase of Nb doping, Nb incorporated FeSe lattice and substituted Fe sites. Thus the texture of tetragonal FeSe become more compact, the superconducting transition temperature is distinctly enhanced up to 13.6 K in FeNb0.04Se, which is enhanced by 27% as compared with that of undoped FeSe, and the upper critical field is enhanced up to 28 T. Moreover, Nb doping can significantly suppress the decay of critical current density with magnetic fields, and then improve the transport performance of FeSe at high magnetic fields.

FeSe has attracted considerable attention over the past few years due to its unique superconductivity and electronic properties. Until now, electron-doping approaches, including interlayer intercalation, K-coating, the interface-induced effect and liquid-gating technology, have been effective methods for enhancing the superconducting transition temperature (Tc) of FeSe bulks or thin films. Due to the multiband nature of FeSe, hole carriers also participate in electrical transport as electron counterparts. However, whether hole doping is able to enhance Tc or not, similarly, heavy electron-doping still remains an open issue. In this work, hole-doping was confirmed in bulk FeSe by adding small amounts of Nb, based on Hall measurements and first-principle theoretical calculations. Subsequently, an enhanced Tc was obtained. Morphology and structural investigations indicated that Nb enters the lattice of β-FeSe by substituting the Fe sites when the amount of Nb added is relatively low. With increased Nb substitution, the Tc value of FeNbxSe0.95 distinctly increases, with the highest value achieved in FeNb0.04Se0.95. Excess Nb addition resulted in the formation of NbxSey impurities and Tc reduction. Hall measurements indicate the dominant nature of hole-type carriers in FeNb0.04Se0.95 below 95 K, and this is in sharp contrast to the un-doped and heavily electron-doped FeSe systems. This result is further verified by first-principle theoretical calculations, which show that Fe0.95Nb0.05Se possesses a larger hole-pocket at the Γ point and a smaller electron-pocket at the M point, compared with FeSe. This work provides a new approach for enhancing the superconductivity of the FeSe system based on hole-doping, and proposes complementary understanding of the intrinsic mechanism of iron-based superconductivity.

Based on microscopic phase field theory, the interatomic potentials of Ni3Al (L1(2) structure) and Ni3Mo (DO22 structure) was calculated employing the inversion calculation method, and their dependence on temperature and concentration are also studied. The inversion calculation results demonstrate that the first nearest neighbor interatomic potentials (WNi-Al and WNi-Mo) increase linearly with the temperature increasing continuously. WNi-Al increases but WNi-Mo decreases linearly with the continuous increase of Al concentration, and vice versa. Substituting the inversion calculated WNi-Al and WNi-Mo at 973 K into the microscopic phase-field kinetics model, the atomic temporal evolution pictures of phase transformation process are similar to the results obtained by empirical interatomic potentials. In addition, the precipitated gamma' phase has a higher ordered degree, which is more consistent with the actual microstructure evolution of phase transformation process than the calculated results reported in previous studies using empirical interatomic potentials.

The microstructural evolutions of the alumina-forming austenitic (AFA) steel subjected to different cold-rolled reductions and then aging at 700 °C were investigated by multiple characterization methods, and the mechanical properties were also examined. The results show that the increased dislocations (especially, edge dislocations) after cold rolling can effectively enhance the volume fraction and refine the particle size of precipitates during initial aging and subsequently accelerate the coarsening rate of precipitates in the AFA steel, resulting in a high coarsening exponent. The coarsening rate of B2–NiAl phase is higher than that of Laves phase. Excellent mechanical properties with a combination of yield strength (1152 ± 32 MPa) and elongation (44.8 ± 4.1%) of cold rolled AFA steel after aging for 2 h can be obtained due to co-strengthening contribution derived from dislocations and precipitates. With the duration of aging, the dislocation strengthening constantly decreases, the effect of precipitation strengthening is contrarily larger than that of dislocations.

In the past few years, iron chalcogenide compounds have attracted considerable attentions due to its unique superconductivity and simplest structure. Till now, many studies have been devoted to explore the superconductivity in iron chalcogenides, including FeSe, FeTe, FeS and their derivatives produced by intermediate doping. However, compared with FeSe, although the superconductivity in S doped FeTe has been widely studied, very few attempts have been reported on the transport properties for this material. Herein the evolution of the superconductivity and the Hall effect up to high S addition levels in FeTe1-xSx (0 ≤ x ≤ 0.5) were studied. It suggests that S substitution for Te sites can effectively suppress the antiferromagnetic ordering and introduce bulk superconductivity in FeTe. The highest Tc ∼9.0 K is achieved in FeTe0.8S0.2 with nominal S content. Hall effect suggests that S addition in FeTe undergoes a reconstruction of hole-type Fermi surface, indicating doping or enhancement of scattering of hole carriers. This work systemically studied the superconductivity of FeTe with S addition and proposes complementary understanding for the intrinsic transport mechanism of iron-based superconductivity.

The improved critical current density was obtained for ex-situ MgB2 bulks initially sintered at 900 °C for 2 h and then at 650 °C for 1 h. It was found that local liquid Mg phase sintering is dominant during first high-temperature sintering process, which results in the formation of MgB2 aggregates with excellent grain connectivity. The second low-temperature sintering process not only can consume part of the residual MgB4 but also enlarge the aggregates zones. Consequently, The MgB2 grain connectivity in sintered samples is enhanced and responsible for the improved critical current density.

Alumina-forming austenitic (AFA) steel with high creep strengths and excellent high-temperature corrosion resistance has a promising potential being applied to high-temperature components of ultra-supercritical power plants. The effect of Cu addition on microstructure and tensile properties of Fe–20Ni–14Cr alumina-forming austenitic (AFA) steel after aging at 973 K has been investigated using various morphology microscopic characterizations and tensile test. The obtained results show that Cu addition promotes the formation of nanoscale B2–NiAl phase in AFA steel, which further increases the tensile strength and ductility of the materials to 1464 MPa and ductility of 23.81%, respectively. By occupying Fe and Ni atoms locations in the nanoscale B2–NiAl phase of AFA steel, Cu atoms reduce the chemical driving force of the nanoscale B2–NiAl phase growth. Such phenomenon results in reduction of the corresponding phase formation energy, and thus improves the phase stability. The occupancy behavior of Cu and its effect on the particle size in nanoscale B2–NiAl phase were quantitatively evaluated by first-principle calculation. The present research work proves that the precipitation strengthening plays a dominant role in the yield strength improvement of AFA steel.

Unlike monolayer Fe-Chalcogenide (Fe-Ch)/SrTiO3 (STO), which possesses the potential for high-temperature superconductivity (HTS), a regular Fe-Ch thin film grown on a non-STO substrate by the pulsed laser deposition method shows totally different superconducting behavior and a different mechanism. Although regular Fe-Ch thick films grown on CaF2 generally show the highest superconducting transition temperature (Tc) compared with any other substrates, the disappearance of superconductivity always takes place when the thickness of the Fe-Ch film is reduced to a critical value (∼20nm for Fe-Se and ∼30nm for Fe-Se-Te) with the reason still under debate. Here, we report an enhanced Tc≈17.6K in a 7-nm-FeTe/7-nm-FeSe bilayer heterostructure grown on CaF2 substrate. Generally, the Fe-Ch film on CaF2 is supposed to be one order of magnitude greater in thickness to achieve similar performance. Hall measurements manifest the dominant nature of hole-type carriers in the films in this work, which is similar to the case of a pressurized bulk FeSe single crystal, while in sharp contrast to heavily electron-doped HTS Fe-Ch systems. According to the electron energy loss spectroscopy results, we observed direct evidence of nanoscale phase separation in the form of a fluctuation of the Fe-L3/L2 ratio near the FeTe/FeSe interface. In detail, a several-unit-cell-thick Fe(Se,Te) diffusion layer shows a higher Fe-L3/L2 ratio than either an FeTe or an FeSe layer, indicating low Fe 3d electron occupancy, which is, to some extent, consistent with the hole-dominant scenario obtained from the Hall results. It also implies a possible relationship between the state of Fe 3d electron occupancy and the enhanced Tc in this work. Our work clarifies the importance of the FeTe/FeSe interface in reviving the superconductivity in Fe-Ch ultrathin films, contributing to a more unified understanding of unconventional Fe-Ch superconductivity.

The Nb3(Al1-xSnx) superconductors (x = 0.05, 0.15, 0.25, 0.35) were prepared by mechanical alloying and subsequent low-temperature sintering. It was found that the critical current density (Jc) of the obtained Nb3(Al1-xSnx) sample is enhanced significantly compared to undoped Nb3Al prepared using the same method. The maximum value of the Jc reaches up to 5.10 × 104 A·cm−2 (4.2 K, 5 T) for Nb3(Al0.85Sn0.15) sample. Combined with the phase composition analysis and microstructure observation, it is indicated that Sn enters the A15 crystal structure of Nb3Al forming the Nb3(Al1-xSnx) phase after low-temperature sintering. What's more, Sn doping improves the grain connectivity as well as refines the grain size of Nb3Al, which are the main reasons for the enhancement of Jc in the Sn doped samples. Based on the exploration of the phase evolution of Nb–Al–Sn system during the mechanical alloying and subsequent low-temperature sintering process, it is also confirmed that Nb3Sn forms firstly during the sintering process and then can serve as the perfect nucleus of Nb3Al to increase its nucleation rate, leading to the significant decrease of the grain size of Nb3Al.

Due to its unique properties, FeSe1−xSx superconductors have been prime candidates to investigate the unconventional superconducting mechanism in iron chalcogenides. In this study, we report the successful preparation of high-quality epitaxial FeSe1−xSx films with x ≤ 0.4 on different substrates via pulsed laser deposition. With different S content, it is found that CaF2 (100) single crystal is the most preferable substrate to use to grow superconducting FeSe1−xSx films. With the increment of S content, the nematic transition temperature (T s) of FeSe1−xSx films decreases simultaneously and disappears at x ≈ 0.2. In contrast to FeSe1−xTex films, the superconducting transition temperature (T c) of FeSe1−xSx films decreases continuously with S doping. And the T c shows no enhancement after the disappearance of T s, suggesting that the nematic transition does not positively impact the superconductivity in these films. In addition to the influence of different S content, it is found that the non-negligible in-plane tensile strain originating mostly from the mismatch between the FeSe1−xSx films and the substrate is the key factor suppressing the superconductivity. Our work can provide constructive guidance for preparing superconducting FeSe1−xSx films and gives a further understanding of the interplay of T s, strain, and superconductivity in iron-chalcogenide films.

A series of planar chiral imidazolium salts derived from [2.2]paracyclophane have been synthesized and characterized. By using these imidazolium salts as carbene precursors, the Rh-catalyzed 1,2-addition of arylboronic acids to aldehydes proceeded readily with low catalyst loadings (0.03–0.3 mol %) and gave a variety of chiral diarylmethanols in excellent yields and moderate enantioselectivities.

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The rhodium-catalyzed addition of arylboronic acids towards aromatic aldehydes proceeds smoothly in the presence of paracyclophane-derived planar chiral imidazolium-based carbene ligands to give the adduct alcohols in excellent yields and up to 52% optical purity.

In the title compound, C8H9N2+·NO3−, intermolecular N—H...O hydrogen bonds join the molecules into a chain extending along the b axis.

A practical Buchwald-Hartwig amination of [2.2]paracyclophanyl bromides with benzhydrylideneamine is developed. The method provides a facile route to a variety of imino and amino [2.2]paracyclophanes that are otherwise not readily synthesized.

A unique family of planar chiral symmetrical N-heterocyclic carbene precursors with restricted flexibility derived from [2.2]paracyclopane were obtained by a new synthetic route. The resolution of 4-amino-13-bromo[2.2]paracyclophane was achieved with relatively high efficiency. Starting from (4 S p,13 R p)-4-amino-13-bromo[2.2]paracyclophane, the planar chiral pseudogem-disubstituted [2.2]paracyclophanyl dihydroimidazoliums were prepared in a four-step sequence with good yields. The resulting dihydroimidazolium salts were fully characterized with a series of methods including single-crystal X-ray diffraction technique.