Hua-Yu Zhang

Observation of the Long Afterglow in AlN Helices.

The coupling effect between nitrogen-vacancies (VN) and aluminum-interstitial sites (Ali) is investigated theoretically and experimentally in AlN helices. First-principles calculations predict a photoluminescence emission peak at approximately 600 nm in AlN doped with complex-defect (VNAli). A typical long afterglow (persistent luminescence) was observed in unintentionally doped AlN helices by introducing the complex-defect of (VNAli). An analysis of the luminescent characteristics indicated that the mechanism behind this afterglow is the complex-defect level and complex-defect density. These findings may further enrich the thoughts of defects in the wide band gap semiconductor of AlN.

Mechanical properties of SiCf/SiC composites with alternating PyC/BN multilayer interfaces

ABSTRACT Alternating pyrolytic carbon/boron nitride (PyC/BN)n multilayer coatings were applied to the KD–II silicon carbide (SiC) fibres by chemical vapour deposition technique to fabricate continuous SiC fibre-reinforced SiC matrix (SiCf/SiC) composites with improved flexural strength and fracture toughness. Three-dimensional SiCf/SiC composites with different interfaces were fabricated by polymer infiltration and pyrolysis process. The microstructure of the coating was characterised by scanning electron microscopy, X–photoelectron spectroscopy and transmission electron microscopy. The interfacial shear strength was determined by the single-fibre push-out test. Single-edge notched beam (SENB) test and three-point bending test were used to evaluate the influence of multilayer interfaces on the mechanical properties of SiCf/SiC composites. The results indicated that the (PyC/BN)n multilayer interface led to optimum flexural strength and fracture toughness of 566.0 MPa and 21.5 MPa m1/2, respectively, thus the fracture toughness of the composites was significantly improved.