Superconductivity in the High-Entropy Ceramics Ti0.2 Zr0.2 Nb0.2 Mo0.2 Ta0.2 Cx with Possible Nontrivial Band Topology.

Topological superconductors have drawn significant interest from the scientific community due to the accompanying Majorana fermions. Here, the discovery of electronic structure and superconductivity (SC) in high-entropy ceramics Ti0.2 Zr0.2 Nb0.2 Mo0.2 Ta0.2 Cx (x = 1 and 0.8) combined with experiments and first-principles calculations is reported. The Ti0.2 Zr0.2 Nb0.2 Mo0.2 Ta0.2 Cx high-entropy ceramics show bulk type-II SC with Tc ≈ 4.00 K (x = 1) and 2.65 K (x = 0.8), respectively. The specific heat jump (∆C/γTc ) is equal to 1.45 (x = 1) and 1.52 (x = 0.8), close to the expected value of 1.43 for the BCS superconductor in the weak coupling limit. The high-pressure resistance measurements show a robust SC against high physical pressure in Ti0.2 Zr0.2 Nb0.2 Mo0.2 Ta0.2 C, with a slight Tc variation of 0.3 K within 82.5 GPa. Furthermore, the first-principles calculations indicate that the Dirac-like point exists in the electronic band structures of Ti0.2 Zr0.2 Nb0.2 Mo0.2 Ta0.2 C, which is potentially a topological superconductor. The Dirac-like point is mainly contributed by the d orbitals of transition metals M and the p orbitals of C. The high-entropy ceramics provide an excellent platform for the fabrication of novel quantum devices, and the study may spark significant future physics investigations in this intriguing material.

Understanding Bridging Sites and Accelerating Quantum Efficiency for Photocatalytic CO2 Reduction.

We report a novel double-shelled nanoboxes photocatalyst architecture with tailored interfaces that accelerate quantum efficiency for photocatalytic CO2 reduction reaction (CO2RR) via Mo-S bridging bonds sites in Sv-In2S3@2H-MoTe2. The X-ray absorption near-edge structure shows that the formation of Sv-In2S3@2H-MoTe2 adjusts the coordination environment via interface engineering and forms Mo-S polarized sites at the interface. The interfacial dynamics and catalytic behavior are clearly revealed by ultrafast femtosecond transient absorption, time-resolved, and in situ diffuse reflectance-Infrared Fourier transform spectroscopy. A tunable electronic structure through steric interaction of Mo-S bridging bonds induces a 1.7-fold enhancement in Sv-In2S3@2H-MoTe2(5) photogenerated carrier concentration relative to pristine Sv-In2S3. Benefiting from lower carrier transport activation energy, an internal quantum efficiency of 94.01% at 380 nm was used for photocatalytic CO2RR. This study proposes a new strategy to design photocatalyst through bridging sites to adjust the selectivity of photocatalytic CO2RR.

Interplay between Charge-Density-Wave, Superconductivity, and Ferromagnetism in CuIr2-xCrxTe4 Chalcogenides.

We report the crystal structure, charge-density-wave (CDW), superconductivity (SC), and ferromagnetism (FM) in CuIr2-xCrxTe4 (0 ≤ x ≤ 2) chalcogenides. Powder x-ray diffraction (PXRD) results reveal that the CuIr2-xCrxTe4 series are distinguished between two structural types and three different regions: (i) layered trigonal structure region, (ii) mixed phase regions, and (iii) spinel structure region. Besides, Cr substitution for Ir site results in rich physical properties including the collapse of CDW, the formation of dome-shaped like SC, and the emergence of magnetism. Cr doping slightly elevates the superconducting critical temperature (Tsc) to its highest Tsc = 2.9 K around x = 0.06. As x increases from 0.3 to 0.4, the ferromagnetic Curie temperature (Tc) increases from 175 to 260 K. However, the Tc remains unchanged in the spinel range of 1.9 ≤ x ≤ 2. This finding provides a comprehensive material platform for investigating the interplay between CDW, SC, and FM multipartite quantum states.

Superconducting dome associated with the suppression and re-emergence of charge density wave states upon sulfur substitution in CuIr2Te4chalcogenides.

We report the path from the charge density wave (CDW)-bearing superconductor CuIr2Te4to the metal insulator transition (MIT)-bearing compound CuIr2S4by chemical alloying with the gradual substitution of S for Te. The evolution of structural and physical properties of the CuIr2Te4-xSx(0 ⩽x⩽ 4) polycrystalline system is systemically examined. The x-ray diffraction (XRD) results imply CuIr2Te4-xSx(0 ⩽x⩽ 0.5) crystallizes in a NiAs defected trigonal structure, whereas it adapts to the cubic spinel structure for 3.6 ⩽x⩽ 4 and it is a mixed phase in the doping range of 0.5

Discovery and Facile Synthesis of a New Silicon Based Family as Efficient Hydrogen Evolution Reaction Catalysts: A Computational and Experimental Investigation of Metal Monosilicides.

A new family of transition-metal monosilicides (MSi, M = Ti, Mn, Fe, Ru, Ni, Pd, Co, and Rh) electrocatalysts with superior electrocatalytic performance of hydrogen evolution is reported, based on the computational and experimental results. It is proposed that these MSi can be synthesized within several minutes by adopting the arc-melting method. The previously reported RuSi is not only fabricated more readily but eventually explored 8 MSi that can be good hydrogen evolution reaction catalysts. Silicides then can be another promising electrocatalysts family as carbides, wherein carbon has the same electronic configuration as silicon. All explored silicides electrodes exhibited low overpotentials (34-54 mV at 10 mA cm-2 ) with Tafel slopes from 23.6 to 32.3 mV dec-1 , which are comparable to that of the commercial 20 wt% Pt/C (37 mV, 26.1 mV dec-1 ). First-principles calculations demonstrated that the superior performance can be attributed to the high catalytic reactivity per site that can even function at high hydrogen coverages (≈100%) on multiple low surface energy facets. The work sheds light on a new class of electrocatalysts for hydrogen evolution, with earth-abundant and inexpensive silicon-based compounds.

NbSeTe-a new layered transition metal dichalcogenide superconductor.

Transition metal dichalcogenides (TMDCs) usually exhibit layered polytypic structures due to the weak interlayer coupling. 2H-NbSe2 is one of the most widely studied in the pristine TMDC family due to its high superconducting transition temperature (T c = 7.3 K) and the occurrence of a charge-density wave (CDW) order below 33 K. The coexistence of CDW with superconductivity poses an intriguing open question about the relationship between Fermi surface nesting and Cooper pairing. Past studies of this issue have mostly been focused on doping 2H-NbSe2 by 3d transition metals without significantly changing its crystal structure. Here we replaced the Se by Te in 2H-NbSe2 in order to design a new 1T polytype layered TMDC NbSeTe, which adopts a trigonal structure with space group P [Formula: see text] m1. We successfully grew large size and high-quality single crystals of 1T-NbSeTe via the vapor transport method using I 2 as the transport agent. Temperature-dependent resistivity and specific heat data revealed a bulk T c at 1.3 K, which is the first observation of superconductivity in pure 1T-NbSeTe phase. This compound enlarged the family of superconducting TMDCs and provides an opportunity to study the interplay between CDW and superconductivity in the trigonal structure.

Multifunctional 2H-TaS2 nanoflakes for efficient supercapacitors and electrocatalytic evolution of hydrogen and oxygen.

Layered transition-metal dichalcogenides based on VIB elements have attracted substantial attention for their applications in energy storage and conversion. However, few studies have concentrated on VB element dichalcogenides. Herein, we report that trifunctional 2H-TaS2 nanoflakes exhibit high performance when applied in supercapacitors, hydrogen evolution reactions (HER) and oxygen evolution reactions (OER). Notably, TaS2 nanoflakes delivered a large volumetric capacitance (502 F cm-3 at the scan rate of 10 mV s-1) and remarkable cycling stability (over 91% after 5000 cycles). TaS2 nanoflakes also exhibited remarkable catalytic performances in HER and OER processes, showing very small overpotentials and Tafel slopes, which are far better than those of the previously reported TaS2 electrocatalysts. Furthermore, TaS2 is highly stable in both alkaline and acidic electrolyte solutions. This work offers a new concept to design VB element-based electrodes for future energy storage and conversion applications.

Origin of Subthreshold Turn-On in Quantum-Dot Light-Emitting Diodes.

The subthreshold (or sub-bandgap) turn-on for electroluminescence is one of the most discussed, but often misinterpreted, phenomena for solution-processed quantum-dot light-emitting diodes. Here, multiple techniques are applied to show that the phenomenon can be readily explained using the fundamental rules of carrier injection and transport. Evident from temperature dependent photovoltage measurements, it is found that the energy up-conversion originating from the decay of charge transfer excitons is not responsible for the subthreshold turn-on. Further analysis using electroabsorption reveals that the turn-on voltage of electroluminescence consistently correlates with the flat-band voltage of the emission layer. Under such subthreshold bias, although the device current is still limited by the depleted hole-transporting layer, field-assisted carrier injection starts to provide enough electrons and holes for detectable radiative recombination, thereby enabling distinct subthreshold turn-on.

Charge transfer-induced photoluminescence in ZnO nanoparticles.

The quality of solution-processed zinc oxide (ZnO) nanoparticles (NPs) is often correlated with their photoluminescence (PL) spectral characteristics. However, the reported PL spectral characteristics lack consistency and remain controversial. Here we report that "defect-emission free" PL spectra can even be obtained in thin films composed of as-synthesized ZnO NPs. It is found that both the PL spectral line-shape and intensity are extremely sensitive to nitrogen and oxygen. By conducting time-dependent PL (t-PL) and photothermal deflection spectroscopy (PDS) measurements under vacuum and different gases, it is proposed that both inert (N2) and reactive (O2) molecules can be absorbed on the ZnO NP surface and induce charge transfer (CT). The CT states induced by N2 are non-radiative which significantly reduces the band emission. Whereas the CT states induced by O2 are radiative at the visible region, and the exciton transfer is efficient which increases the overall PL quantum yield. Owing to such effects, the previously reported correlation between defects and PL emission becomes questionable and needs to be revisited. Particularly, the visible emission from the ZnO NPs is proved to be facilitated by external effects, instead of direct recombination from defect states.

Epidemiological investigation of non-albicans Candida species recovered from mycotic mastitis of cows in Yinchuan, Ningxia of China.

BACKGROUND: Candida spp. is the vital pathogen involved in mycotic mastitis of cows. However the epidemiology and infection of Candida species in mycotic mastitis of cow in Ningxia province of China has not been explored. In the present study, the epidemiology, antimicrobial susceptibility and virulence-related genes of non-albicans Candida (NAC) species were investigated. METHODS: A total of 482 milk samples from cows with clinical mastitis in four herds of Yinchuan, Ningxia were collected and used for the isolation and identification of mastic pathogens by phenotypic and molecular characteristics, and matrix-assisted laser desorption ionization-time of flight mass spectrometry. The antimicrobial susceptibility to antifungal agents was also determined by a disk diffusion assay. The presence of virulence-related genes was determined by polymerase chain reaction (PCR). RESULTS: A total of 60 isolates from nine different Candida species were identified from 256 (60/256, 23.44%) milk samples. The most frequently identified species in cows with clinical mastitis groups were Candida krusei (n = 14) and Candida parapsilosis (n = 6). Others include Candida lipolytica, Candida lusitaniae, Cryptococcus neoformans. But no Candida albicans was identified in this study. Interestingly, All C. krusei isolates (14/14) were resistant to fluconazole, fluorocytosine, itraconazole and ketoconazole, 2 out of 14 C. krusei were resistant to amphotericin, and 8 out of the 14 were resistant to nystatin. Similarly, all six C. parapsilosis isolates were resistant to fluorocytosine, but susceptible to fluconazole, ketoconazole and nystatin; two of the six were resistant amphotericin and itraconazole. Molecularly, all of the C. parapsilosis isolates carried eight virulence-related genes, FKS1, FKS2, FKS3, SAP1, SAP2, CDR1, ERG11 and MDR1. All of the C. krusei isolates contained three virulence-related genes, ERG11, ABC2 and FKS1. CONCLUSION: These data suggested that Candida species other than C. albicans played a pathogenic role in mycotic mastitis of cows in Yinchuan, Ningxia of China. The high incidence of drug-resistant genes in C. parapsilosis and C. krusei also highlighted a great concern in public and animal health in this region.

Global Transcriptome Changes of Biofilm-Forming Staphylococcus epidermidis Responding to Total Alkaloids of Sophorea alopecuroides.

Transcriptome changes of biofilm-forming Staphylococcus epidermidis response to total alkaloids of Sophorea alopecuroides was observed. Bioinformatic analyses were further used to compare the differential gene expression between control and the treated samples. It was found that 282 genes were differentially expressed, with 92 up-regulated and 190 down-regulated. These involved down-regulation of the sulfur metabolism pathway. It was suggested that inhibitory effects on Staphylococcus epidermidis and its biofilm formation of the total alkaloids of S. alopecuroides was mainly due to the regulation of the sulfur metabolism pathways of S. epidermidis.

Endohedral gallide cluster superconductors and superconductivity in ReGa5.

We present transition metal-embedded (T@Gan) endohedral Ga-clusters as a favorable structural motif for superconductivity and develop empirical, molecule-based, electron counting rules that govern the hierarchical architectures that the clusters assume in binary phases. Among the binary T@Gan endohedral cluster systems, Mo8Ga41, Mo6Ga31, Rh2Ga9, and Ir2Ga9 are all previously known superconductors. The well-known exotic superconductor PuCoGa5 and related phases are also members of this endohedral gallide cluster family. We show that electron-deficient compounds like Mo8Ga41 prefer architectures with vertex-sharing gallium clusters, whereas electron-rich compounds, like PdGa5, prefer edge-sharing cluster architectures. The superconducting transition temperatures are highest for the electron-poor, corner-sharing architectures. Based on this analysis, the previously unknown endohedral cluster compound ReGa5 is postulated to exist at an intermediate electron count and a mix of corner sharing and edge sharing cluster architectures. The empirical prediction is shown to be correct and leads to the discovery of superconductivity in ReGa5. The Fermi levels for endohedral gallide cluster compounds are located in deep pseudogaps in the electronic densities of states, an important factor in determining their chemical stability, while at the same time limiting their superconducting transition temperatures.

Superconductivity in 3R-Ta(1-x)M(x)Se2 (M = W, Mo).

The 3-layer rhombohedral (3R) polytype of TaSe2-x Te x is known to display a superconducting transition temperature that is between 6 and 17 times higher than that of the two-layer hexagonal (2H) polytype. The remarkable difference in T c, although clearly associated with a difference in polytype, could have been due to an electronic effect specific to the Te-Se substitution. Here we report that small amounts of Mo or W doping lead to a 2H to 3R polytype transition in Ta1-x Mo x Se2 and Ta1-x W x Se2. The 3R polytype materials are again found to have substantially higher T c (~2 K for Ta0.9W0.1Se2 and Ta0.9Mo0.1Se2) than the 2H material (0.15 K), eliminating the possibility that any special characteristics of the Te/Se substitution are responsible for the dramatic difference in T c. We infer that a three-layer stacking sequence is strongly preferred for superconductivity over a two-layer stacking sequence in the TaSe2 system.

Characterization of the heavy metal pyrochlore lattice superconductor CaIr2.

We report the electronic properties of the cubic laves phase superconductor CaIr2(Tc = 5.8 K), in which the Ir atoms have a pyrochlore lattice. The estimated superconducting parameters obtained from magnetization and specific heat measurements indicate that CaIr2 is a weakly coupled BCS superconductor. Electronic band structure calculations show that the Ir d-states are dominant at the Fermi level, creating a complex Fermi surface that is impacted substantially by spin-orbit coupling.

Polytypism, polymorphism, and superconductivity in TaSe(2-x)Te(x).

Polymorphism in materials often leads to significantly different physical properties--the rutile and anatase polymorphs of TiO2 are a prime example. Polytypism is a special type of polymorphism, occurring in layered materials when the geometry of a repeating structural layer is maintained but the layer-stacking sequence of the overall crystal structure can be varied; SiC is an example of a material with many polytypes. Although polymorphs can have radically different physical properties, it is much rarer for polytypism to impact physical properties in a dramatic fashion. Here we study the effects of polytypism and polymorphism on the superconductivity of TaSe2, one of the archetypal members of the large family of layered dichalcogenides. We show that it is possible to access two stable polytypes and two stable polymorphs in the TaSe(2-x)Te(x) solid solution and find that the 3R polytype shows a superconducting transition temperature that is between 6 and 17 times higher than that of the much more commonly found 2H polytype. The reason for this dramatic change is not apparent, but we propose that it arises either from a remarkable dependence of Tc on subtle differences in the characteristics of the single layers present or from a surprising effect of the layer-stacking sequence on electronic properties that are typically expected to be dominated by the properties of a single layer in materials of this kind.

A large family of filled skutterudites stabilized by electron count.

The Zintl concept is important in solid-state chemistry to explain how some compounds that combine electropositive and main group elements can be stable at formulas that at their simplest level do not make any sense. The electronegative elements in such compounds form a polyatomic electron-accepting molecule inside the solid, a 'polyanion', that fills its available energy states with electrons from the electropositive elements to obey fundamental electron-counting rules. Here we use this concept to discover a large family of filled skutterudites based on the group 9 transition metals Co, Rh, and Ir, the alkali, alkaline-earth, and rare-earth elements, and Sb4 polyanions. Forty-three new filled skutterudites are reported, with 63 compositional variations--results that can be extended to the synthesis of hundreds of additional new compounds. Many interesting electronic and magnetic properties can be expected in future studies of these new compounds.

A novel CO2-stable dual phase membrane with high oxygen permeability.

By cobalt-doping of the mixed conducting phase PSFC, a good combination of high CO2 stability and high oxygen permeability is obtained for the 60 wt% Ce(0.9)Pr(0.1)O(2-δ)-40 wt% Pr(0.6)Sr(0.4)Fe(0.5)Co(0.5)O(3-δ) (CP-PSFC) dual phase membrane, which suggests that CP-PSFC is a promising membrane for industrial applications in the oxyfuel process for CO2 capture.

Natural gas to fuels and chemicals: improved methane aromatization in an oxygen-permeable membrane reactor.

Adding value with membranes: Improved methane aromatization was achieved by using an oxygen-permeable membrane. The resulting membrane reactor shows a superior methane conversion and a higher resistance towards catalyst deactivation.