Silicon carbide (SiC) nanofibers are attractive for electromagnetic wave (EMW) absorption in harsh environments, but the controllable construction of hollow architectures and the enhancement of dielectric loss remain challenging. Herein, phase-separation-enabled hollow SiC composite nanofibers with multiscale interfacial structures were developed to address these issues. By combining phase-field simulations with experiments, liquid-liquid phase separation was identified as the key factor governing radial compositional segregation and hollow-fiber formation, enabling controllable regulation of the phase constitution, defect density, and interfacial structure through the precursor ratio. The hollow architecture, together with the resulting multiscale interfaces and abundant defects, synergistically enhanced dielectric loss and improved impedance matching. At a PVP/PSN mass ratio of 2:1, the sample obtains a minimum reflection loss of -56.11 dB at 1.53 mm, while the 1:1 hollow fiber delivered the broadest effective absorption bandwidth of 4.96 GHz at 1.39 mm. After incorporation into an AlPO₄ matrix, the optimized fibers enabled stable EMW absorption from 298 to 873 K, with a maximum effective absorption bandwidth of 4.08 GHz in the X-band. This work demonstrates a controllable route for constructing hollow silicon carbide-based fibrous absorbers and provides insight into multiscale interfacial design for EMW absorption over a wide temperature range.

BN/La–Al–Si–O composite ceramics were fabricated by hot-pressed sintering using hexagonal boron nitride (h-BN), lanthanum oxide (La₂O₃), aluminia (Al₂O₃), and amorphous silica (SiO₂) as the raw materials. The effects of sintering temperature on microstructural evolution, bulk density, apparent porosity, and mechanical properties of the h-BN composite ceramics were investigated. The results indicated that La–Al–Si–O liquid phase was formed during sintering process, which provided an environment for the growth of h-BN grains. With increasing sintering temperature, the cristobalite phase precipitation and h-BN grain growth occurred at the same time, which had a significant influence on the densification and mechanical properties of h-BN composite ceramics. The best mechanical properties of BN/La–Al–Si–O composite ceramics were obtained under the sintering temperature of 1700 ℃. The elastic modulus, flexural strength, and fracture toughness were 80.5 GPa, 266.4 MPa, and 3.25 MPa·m^1/2, respectively.