Physical Understanding of Active Control of Beam Scanning in Preventing Top Concavity in Electron Beam Welding

Metallurgical and Materials Transactions A - Low-frequency scanning electron beam welding (SEBW) is recently recognized as a possible control method for preventing the top concavity behavior in...     

Influence of addition of nanosize barium cerate on the microstructure and properties of top-seeded melt growth YBCO bulk superconductors

Barium cerate (BaCeO₃) is one of the possible additions to bulk YBa₂Cu₃O₇ single-grain superconductors to suppress the growth of Y₂BaCuO₅ (Y211) particles. This paper investigates the synthesis of barium cerate powder and its use in YBa₂Cu₃O₇ bulk superconductors. Crystalline barium cerate was synthesized by solid-state reaction, by co-precipitation of oxalates and by sol-gel method. Final calcination was held in air or in vacuum. It is shown that the most efficient in refining Y211 is nanocrystalline barium cerate prepared by sol-gel method calcined in vacuum. The effective refinement of Y211 particles occurred over the entire interval of nanocrystalline BaCeO₃ addition from 0.38 to 1.90 wt%. The optimal concentration of nanosize barium cerate was determined, microstructure and superconducting properties were characterized. The effect of Y211 content on trapped field in YBCO bulks with addition of nanocrystalline barium cerate is shown.     

Influence of Radiation on the Properties and the Stability of Hybrid Perovskites

Organic–inorganic perovskites are well suited for optoelectronic applications. In particular, perovskite single and perovskite tandem solar cells with silicon are close to their market entry. Despite their swift rise in efficiency to more than 21%, solar cell lifetimes are way below the needed 25 years. In fact, comparison of the time when the device performance has degraded to 80% of its initial value (T₈₀ lifetime) of numerous solar cells throughout the literature reveals a strongly reduced stability under illumination. Herein, the various detrimental effects are discussed. Most notably, moisture‐ and heat‐related degradation can be mitigated easily by now. Recently, however, several photoinduced degradation mechanisms have been observed. Under illumination, mixed perovskites tend to phase segregate, while, further, oxygen catalyzes deprotonation of the organic cations. Additionally, during illumination photogenerated charge can be trapped in the N? H antibonding orbitals causing dissociation of the organic cation. On the other hand, organic–inorganic perovskites exhibit a high radiation hardness that is superior to crystalline silicon. Here, the proposed degradation mechanisms reported in the literature are thoroughly reviewed and the microscopic mechanisms and their implications for solar cells are discussed.