Chemical bonding of oxygen in intergranular amorphous layers in high-purity β-SiC ceramics

Abstract

An amorphous intergranular layer, 0.4 nm thick, is found by high-resolution transmission electron microscopy of β-SiC ceramics fabricated by the HIP glass-encapsulation technique without the use of additives. The intergranular layer is found to contain oxygen, which may also be present in the SiC grains near the grain boundary. The mean composition of the intergranular layer is determined to be SiO 0.10±0.01C 0.93±0.04, whose C/O ratio is close to a hypothetical Si-oxycarbide stoichiometry. Electron energy loss spectroscopy shows that both the Si-L 23 and O-K edges from the intergranular layer are distinctive compared to those of SiC and/or SiO 2. This provides direct evidence of the presence of oxygen in a chemical environment different to that in glassy SiO 2, that can also be found in the intergranular layer. First principle calculations by the DV-X α method using an interface model cluster, satisfactorily reproduce the chemical shifts of the energy loss near edge structure (ELNES) for both the Si-L 23 and O-K edges.