An asymmetrical tilt grain boundary which was free of any intergranular film was found between two Si3N4 grains in a Si3N4-SiC composite. It was found that the orientational relationship between the 2 grains was best described, in deformation twinning terms, as a type-I twinning operation with K1 = (5¯11). An equivalent, but less satisfactory, description was that the orientational relationship was close to a  = 9 near-coincident site lattice which would be the ideal such lattice for a c/a ratio of 1/8.

K.M.Knowles, S.Turan: Materials Science Forum, 1996, 207-209, 353-6