Microstructural evolution of amorphous Si 2 BC 3 N nanopowders upon heating at high temperatures: High pressures reverse the nucleation order of SiC and BN (C)

Amorphous Si 2 BC 3 N nanopowders ( NP s) were heated at 1000‐1700°C temperatures for 30 minutes in 1 atm N 2 . The changes in phases, chemical bonds, and microstructures were investigated by XRD , XPS , NMR , TEM , and first‐principles calculation. Increases in heating temperatures lead to the nucleation and growth of SiC and BN (C) grains, along with partial transformation of SiC 4 units from amorphous to β/α‐SiC, and collapse of B–C–N bonds. SiC nucleates prior to BN (C) at 1 atm, while it goes in the opposite order at high pressures (≥1 GP a). High pressures also shift the initial temperatures of crystallization of amorphous Si 2 BC 3 N NP s from 1400°C (1 atm) to 1150°C (5 GPa).