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Application of acoustic emission and laser optoacoustics at various stages of defect formation during friction stir welding
摘要： This paper covers basic aspects of laser ultrasound and acoustic emission non-destructive testing methods in application of monitoring friction stir welds during its deformation and fracture. Stress-strain curves for such welds were obtained and the mechanical characteristics of welded joints of aluminum-magnesium alloy were determined. Using acoustic elastic effect levels of mechanical stresses were measured. Signals of acoustic emission, stimulated by one-axis loading, were registered and analyzed. It was established that acoustic emission during deformation and fracture of samples of welded joints is associated with the course of the process of plastic flow of the material. The nature of the distribution of acoustic emission parameters in the destruction of welded joints with defects has distinctive features. In conditions of one axis quasi static loading rate event count acoustic emission is the most informative parameter.
关键词： friction stir welding,laser optoacoustics,aluminum-magnesium alloy,acoustic emission,defect formation
更新于2025-09-16 10:30:52
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Codoping Er-N to Suppress Self-Compensation Donors for Stable <i>p</i> -Type Zinc Oxide
摘要： Stable p-type doping of zinc oxide (ZnO) is an unsolved but critical issue for ultraviolet optoelectronic applications despite extensive investigations. Here, an Er-N codoping strategy for defect engineering of ZnO to suppress the self-compensation of the donor-type intrinsic point defects (IPDs) over the acceptor-type ones is proposed. Via first-principles calculations, the influence of nitrogen and erbium concentration on the stability of ZnO is investigated. The complex (ErZn-mNO) consisting of multiple substitutional N on O sites and one substitutional Er on Zn site is a crucial stabilizer. With an increase of the concentration of N, the absorption edges redshift to lower energy due to the impurity band broadening in the bandgap. The results suggest that codoping Er-N into the ZnO matrix is a feasible way to manufacture stable p-type ZnO.
关键词： p-type ZnO,Er-N codoping,first principles,defect formation energy
更新于2025-09-10 09:29:36
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Synergistic Effect of the Electronic Structure and Defect Formation Enhances Photocatalytic Efficiency of Gallium Tin Oxide Nanocrystals
摘要： The design of photocatalysts with enhanced efficiency is pivotal to sustainable environmental remediation and renewable energy technologies. Simultaneous optimization of different factors affecting the performance of a photocatalyst, including the density of active surface sites, charge carrier separation, and valence and conduction band redox potentials, remains challenging. Here we report the synthesis of ternary gallium tin oxide (GTO) nanocrystals with variable composition, and investigate the role of Ga3+ dopants in altering the electronic structure of rutile-type SnO2 nanocrystal lattice using steady-state and time-resolved photoluminescence spectroscopies. Substitutional incorporation of Ga3+ increases the band gap of SnO2 nanocrystals, imparting the reducing power to the conduction band electrons, and causes the formation of acceptor states, which, in conjunction with electron trapping by donors (oxygen vacancies), leads to stabilization of the photoexcited carriers. Combination of a decrease in the charge recombination rate and adjustment of the conduction band reduction potential to more negative values synergistically promote the photocatalytic efficiency of the GTO nanocrystals. The apparent rate constant for the photocatalytic degradation of rhodamine-590 dye by optimally prepared GTO NCs is 0.39 min-1, more than two times greater than that by benchmark Aeroxide TiO2 P25 photocatalyst. The results of this work highlight the concept of using rational aliovalent doping of judiciously chosen metal oxide nanocrystal lattices to simultaneously manipulate multiple photocatalytic parameters, enabling the design of versatile and highly efficient photocatalysts.
关键词： photocatalysts,photocatalytic efficiency,nanocrystals,electronic structure,gallium tin oxide,defect formation
更新于2025-09-09 09:28:46