Microstructural evolution of amorphous Si2BC3N nanopowders upon heating at high temperatures: High pressures reverse the nucleation order of SiC and BN(C)

Amorphous Si2BC3N nanopowders (NPs) were heated at 1000-1700 degrees C temperatures for 30minutes in 1atm 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 SiC4 units from amorphous to /-SiC, and collapse of B-C-N bonds. SiC nucleates prior to BN(C) at 1atm, while it goes in the opposite order at high pressures (1 GPa). High pressures also shift the initial temperatures of crystallization of amorphous Si2BC3N NPs from 1400 degrees C (1atm) to 1150 degrees C (5GPa).