EPR investigations are performed in SIC and SiOC nanometric powders an
nealed between 1200 and 1800 degrees C. By using different EPR frequen
cy bands and a suitable spectra analysis, three quite different parama
gnetic defects with well defined (g) over tilde(i) (i = 1, 2, 3) and h
yperfine (A) over tilde(i) (i = 1, 2) tensors account for the EPR sign
al 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 t
o) = 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 we
ll as amorphous SiC and carbon present in minor concentration in the n
etwork. In SiOC powders, the above defects are evidenced only at high
annealing temperature (T-a greater than or equal to 1200 degrees C) wh
en the oxygen contained is highly reduced.