A Simple Urea Approach to N-Dopedα-Mo_(2)C with Enhanced Superconductivity

Chemical doping is a critical factor in the development of new superconductors or optimizing the superconducting transition temperature(T_(c))of the parent superconducting materials.Here,a new simple urea approach is developed to synthesize the N-dopedα-Mo_(2)C.Benefiting from the simple urea method,a broad superconducting dome is found in the Mo_(2)C1−xNx(0≤x≤0.49)compositions.X-ray diffraction results show that the structure of𝛼α-Mo_(2)C remains unchanged and there is a variation of lattice parameters with nitrogen doping.Resistivity,magnetic susceptibility,and heat capacity measurement results confirm that T_(c)was strongly increased from 2.68K(x=0)to 7.05K(x=0.49).First-principles calculations and our analysis indicate that increasing nitrogen doping leads to a rise in the density of states at the Fermi level and doping-induced phonon softening,which enhances electron–phonon coupling.This results in an increase in𝑇T_(c)and a sharp rise in the upper critical field.Our findings provide a promising strategy for fabricating transition metal carbonitrides and provide a material platform for further study of the superconductivity of transition metal carbides.

Green fabrication of nickel-iron layered double hydroxides nanosheets efficient for the enhanced capacitive performance

Rational synthesis of robust layered double hydroxides(LDHs) nanosheets for high-energy supercapacitors is full of challenges.Herein,we reported an ultrasonication-assisted strategy to eco-friendly fabricate NiFe-LDHs nanosheets for the enhanced capacitive behavior.The experimental results combined with different advanced characterization tools document that the utilization of ultrasonication has a profound effect on the morphology and thickness of the as-obtained NiFe-LDHs,alternatively affecting the capacitive behavior.It shows that NiFe-LDHs nanosheets prepared with 2-h ultrasonic treatments display the exceptional capacitive performance because of the synergetic effect of ultrathin thickness,large specific surface area,and high mesoporous volume.The maximum specific capacitance of Ni_(3) Fe_(1)-LDHs nanosheets with the thickness of 7.39 nm and the specific surface area of 77.16 m~2 g^(-1) reached 1923 F g^(-1),which is competitive with most previously reported values.In addition,the maximum specific energy of the assembled NiFe-LDHs//AC asymmetric supercapacitor achieved 49.13 Wh kg^(-1) at400 W kg^(-1).This work provides a green technology to fabricate LDHs nanosheets,and offers deep insights for understanding the relationship between the morphology/structure and capacitive behavior of LDHs nanosheets,which is helpful for achieving high-performance LDHs-based electrode materials.

Superconductivity and Charge Density Wave in Iodine-Doped CuIr_(2)Te_(4)

We report a systematic investigation on the evolution of the structural and physical properties,including the charge density wave(CDW) and superconductivity of the polycrystalline CuIr_(2)Te_(4-x)Ix for 0.0 ≤x≤ 1.0.Xray diffraction results indicate that both of a and c lattice parameters increase linearly when 0.0 ≤ x ≤ 1.0.The resistivity measurements indicate that the CDW is destabilized with slight x but reappears at x≥0.9 with very high TCDW.Meanwhile,the superconducting transition temperature Tc enhances as x increases and reaches a maximum value of around 2.95 K for the optimal composition CuIr_(2)Te_(1.9)I_(0.1) followed by a slight decrease with higher iodine doping content.The specific heat jump(ΔC/γTc) for the optimal composition CuIr_(2)Te_(3.9)I_(0.1) is approximately 1.46,which is close to the Bardeen-Cooper-Schrieffer value of 1.43,indicating that it is a bulk superconductor.The results of thermodynamic heat capacity measurements under different magnetic fields |Cp(T,H)],magnetization M(T,H) and magneto-transport ρ(T,H) measurements further suggest that CuIr_(2)Te_(4-x)Ix bulks are type-Ⅱ superconductors.Finally,an electronic phase diagram for this CuIr_(2)Te_(4-x)Ix system has been constructed.The present study provides a suitable material platform for further investigation of the interplay of the CDW and superconductivity.

Facile synthesis of Ni-,Co-,Cu-metal organic frameworks electrocatalyst boosting for hydrogen evolution reaction

The conductive metal-organic frameworks(MOFs)are suggested as the ideal electrocatalysts for hydrogen evolution reaction(HER)because of the high utilization of metal atoms.Rational design and facile synthesis of MOFs with large specific surface area,proper metals as center,and tunable chemical components is still full of challenges.Herein,we report the facile synthesis three types of porous MOFs by regulating metal center using benzene-1,3,5-tricarboxylic acid(H3 BTC)as organic ligand and have successfully synthesized the rhombic octahedral Cu-BTC,rod-shaped Co-BTC and spherical Ni-BTC materials with large specific surface area ranged in 350-500 m^(2)g^(-1).These as-prepared MOFs materials exhibit high performance of HER in 0.5 M H_(2)SO_(4).Ni-BTC material exhibits the lowest overpotential of 53 mV at 10 mA cm-2 and the smallest Tafel slope of 62 mV dec^(-1)than those of Cu-BTC(270 mV,155 mV dec^(-1))and Co-BTC(123 mV,100 mV dec^(-1)),which are much superior to these previously reported MOFs catalysts.In addition,the fast catalytic kinetic of Ni-BTC was confirmed by the smaller charge transfer resistance(Rct)value of 0.9Ωand larger electrochemical active surface area(ECSA)of 35.5 cm^(2)than those of Cu-BTC(8.2Ω,22.5 cm^(2))and Co-BTC(1.9Ω,27.7 cm^(2)).Because of the structural advantage and large ECSA,the turnover frequency(TOF)value of Ni-BTC reaches up to 0.041 s-1 at 120 mV overpotential,which is 20.5 and 2.6 times greater than that of Cu-BTC(0.002 s-1)and Co-BTC(0.016 s-1).Besides,these three types of MOFs exhibited excellent durability over 12 h.This study unfolds diverse insights into the design and facile synthesis of MOFs for electrochemical energy conversion system.

Extremely strong coupling s-wave superconductivity in the medium-entropy alloy TiHfNbTa

Here we report a TiHfNbTa bulk medium-entropy alloy(MEA)superconductor crystallized in the body-centered cubic structure with the unit cell parameter a=3.35925?,which is synthesized by an arc melting method.Superconducting properties of the TiHfNbTa are studied by employing magnetic susceptibility,resistivity,and specific heat measurements.Experimental results show a bulk superconducting transition temperature(Tc)of around 6.75 K.The lower and upper critical fields for TiHfNbTa are45.8 m T and 10.46 T,respectively.First-principles calculations show that the d electrons of Ti,Hf,Nb,and Ta are the main contribution to the total density of states near the Fermi level.Our results indicate that the superconductivity is a conventional swave type with extremely strong coupling(△C_(el)/γ_(n)T_(c)=2.88,2△_(0)/k_(B)T_(c)=5.02,and λ_(ep)=2.77).The extremely strong coupling behavior in the s-wave type Ti Hf Nb Ta MEA superconductor is unusual because it generally happens in cuprates,pnictides,and other unconventional superconductors.