The formation of chemical/structural gradients in strong covalent bonded SiBN fibers under active nitrogen atmosphere

In this work, SiBN fibers with chemical/structural gradients under the radial direction were fabricated by onestep treatment at 1700 ?C under active nitrogen atmosphere. The formation of chemical gradient should be contributed to the boron atoms diffusion from the fiber interior to the surface, under the driven force of B?N bond-breaking in Si?N?B networks to form stable B?N bonds in the B?N?B networks at the fiber surface. Meanwhile, the structural gradients with graded phase separation of Si?N?B networks and crystallization behavior of Si3N4 phase could form under the effect of graded boron content distribution. The SiBN fibers with chemical/structural gradients showed better high-temperature stability due to the possibly synergistic effect of the decomposition resistant of boron-rich surface and the optimization of graded boron distribution. We expect our finding as a universal method to fabricate chemical/structural gradients on other boron-containing multinary ceramics with various shapes.