EPR investigations of SiC and SiOC nanometric powders

EPR investigations are performed in SIC and SiOC nanometric powders annealed between 1200 and 1800 degrees C. By using different EPR frequency bands and a suitable spectra analysis, three quite different paramagnetic defects with well defined (g) over tilde(i) (i = 1, 2, 3) and hyperfine (A) over tilde(i) (i = 1, 2) tensors account for the EPR signal in these materials. The defects are characterized by (g) over tilde(1) (g(1)(parallel to) = 2.0046(3), g(1)(perpendicular to)2.0023(3)), (g) over tilde(2) (g(2)(parallel to) = 2.0037(3), g(2)(perpendicular to) = 2.0028(3)) and an isotropic (g) over tilde(3) (2.0030(3)) tensors. In SiC powders, the defects assignment is discussed with respect to the different SiC forms, namely alpha-SiC and beta-SiC polytypes as well as amorphous SiC and carbon present in minor concentration in the network. In SiOC powders, the above defects are evidenced only at high annealing temperature (T-a greater than or equal to 1200 degrees C) when the oxygen contained is highly reduced.