Correlation between local structure variations and critical temperature of (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(TiO2)x superconductor

TiO₂ doping content affects the critical temperature (T_c) and the variations of local structure on Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ. The (Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ)_1-x(TiO₂)_x samples were fabricated with the solid-state reaction process, where x = 0, 0.002, 0.004, 0.006, 0.008, and 0.01. The T_c values of the samples were obtained by measuring resistivity versus temperature, indicating that T_c gradually decreased with increasing doping content (x). To explain the obtained degradation of T_c, carrier properties, role of interlayer coupling, and local structure were systematically investigated using Azlamozov–Larkin theory and its Lawrence–Doniach modification for strong anisotropic superconductors. The calculation of excess conductivity at the mean field region showed that the c-axis coherence length (ξ_c) and the effective inter-layering spacing (d) increased with increasing doping content. X-ray diffraction patterns also showed that the bond distances increased with increasing TiO₂ content. The copper valence (V) and carrier concentration (p) of the samples were determined by analyzing the Cu L_2,3-edge X-ray absorption near edge structure spectra. The values of V and p showed the same trend of decreasing with increasing x. A close correlation between the changes in local structure parameters and degradation of T_c of (Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ)_1-x(TiO₂)_x was then probably concluded.     

Hydrothermal synthesis of CuO/rGO nanosheets for enhanced gas sensing properties of ethanol

In this work, CuO nanosheets and CuO/rGO nanocomposites are synthesized by one-step hydrothermal method and characterized accordingly. Next, these samples are tested for gas sensing performance. The test data show that the CuO/rGO sensors have significantly improved gas sensing performance for ethanol compared to the pure CuO sensor. It should be noted that the CuO/rGO-10 sensor has the most outstanding gas sensing performance among the four sensors prepared, with an optimum working temperature 25 lower than that before doping, and its response value for 100 ppm ethanol at 175 °C is 10.54, which is 3.75 times higher than that before rGO doping. Also, the CuO/rGO-10 sensor has remarkable selectivity and reproducibility for ethanol. Most importantly, its limit of detection for ethanol is 100 ppb. At last, the gas sensing mechanism of the composites for ethanol is explained. Enhanced gas sensing performance of CuO/rGO sensors for ethanol is attributed to the lamellar structure and the synergistic effect between CuO and rGO.     

Mechanism of Cf/SiC hole making with high shape precision using abrasive waterjet based on response surface method

This paper aims to explore the accurate control of hole shape for AWJ hole-making of C_f/SiC based on experimental and mathematical analysis methods, and the influence mechanism involved is emphatically analyzed. The results reveal that D_difference is most influenced by the standoff distance, followed by the traverse speed, while it is less influenced by the pressure and the abrasive flow rate. The traverse speed, pressure and abrasive flow rate affect the D_difference by changing the total energy of the jet; while the standoff distance mainly affects the D_difference by changing the effective impact area, which is fundamentally different from other process parameters. In terms of interaction effects, decreasing the traverse speed and increasing the waterjet pressure can amplify the effect of interaction with the involvement of the standoff distance on the D_difference. Based on the established D_difference model and D_offset model, a control method that can gain acquired hole shape is finally obtained for selecting the process parameters of AWJ machining.