Influence of vanadium doping on the behavior of YBa_2Cu_3O_7-y

YBa2Cu3-xVxO7-y(x=0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) superconductors have been prepared. X-ray diffraction shows that the system remains orthorhombic for all compositions studied, but for x > 0.4 V2O5 was detected as an impurity phase. Substitution of V5+ for Cu2+ occurs in the Cu(2) sites on the Cu(2)-O planes. The introduction of the high valence element, vanadium, produces the extra free-electrons. These electrons recombine with the positive carrier of the system. It makes depression of the mobility and the Hall number of YBa2Cu3-xVxO7-v and also results in a depression of TC.

A Compensation Mechanism for Semi-Insulating 6H-SiC Doped with Vanadium

A model is presented to describe a compensation mechanism for semi-insulating 6H-SiC grown with the intentional doping of vanadium. Because we found nitrogen to be the principal shallow donor impurity in SiC by secondary ion mass spectroscopy （SIMS） measurements, semi-insulating properties in SiC are achieved by compensating the nitrogen donor with the vanadium deep acceptor level. The presence of different vanadium charge states V^3＋ and V^4＋ is detected by electron paramagnetic resonance and optical absorption measurements,which coincides with the results obtained by SIMS measurements. Both optical absorption and low temperature photoluminescence measurements reveal that the vanadium acceptor level is located at 0.62eV below the conduction band in 6H-SiC.

Deep Level Transient Fourier Spectroscopy and Photoluminescence of Vanadium Acceptor Level in n-Type 4H-SiC

Deep level transient Fourier spectroscopy （DLTFS） measurements are used to characterize the deep impurity levels in n-type 4H-SiC by vanadium ions implantation. Two acceptor levels of vanadium at Ec - 0.81 and Ec - 1.02eV with the electron capture cross section of 7.0 × 10^16 and 6.0 × 10^-16 cm^2 are observed, respectively. Low-temperature photoluminescence measurements in the range of 1.4-3.4eV are also performed on the sample, which reveals the formation of two electron traps at 0.80 and 1. 16eV below the conduction band. These traps indicate that vanadium doping leads to the formation of two deep acceptor levels in 4H-SiC,with the location of 0.8±0.01 and 1. 1 ±0.08eV below the conduction band.

Tuning the electronic structure of NiCoP arrays through V doping for pH-universal hydrogen evolution reaction electrocatalyst

The exploration of cost-effective,high-performance,and stable electrocatalysts for the hydrogen evolution reaction(HER)over wide pH range(0–14)is of paramount importance for future renewable energy conversion technologies.Regulation of electronic structure through doping vanadium atoms is a feasible construction strategy to enhance catalytic activities,electron transfer capability,and stability of the HER electrode.Herein,V-doped NiCoP nanosheets on carbon fiber paper(CFP)(denoted as Vx-NiCoP/CFP)were constructed by doping V modulation on NiCoP nanosheets on CFP and used for pH-universal HER.Benefiting from the abundant catalytic sites and optimized hydrogen binding thermodynamics,the resultant V15-NiCoP/CFP demonstrates a significantly improved HER catalytic activity,requiring overpotentials of 46.5,52.4,and 85.3 mV to reach a current density of 10 mA·cm^(−2)in 1 mol·L^(−1) KOH,0.5 mol·L^(−1) H_(2)SO_(4),and 1 mol·L^(−1) phosphate buffer solution(PBS)electrolytes,respectively.This proposed cation-doping strategy provides a new inspiration to rationally enhance or design new-type nonprecious metal-based,highly efficient,and pH-universal electrocatalysts for various energy conversion systems.