High resolution transmission electron microscopy of grain boundaries between hexagonal boron nitride grains in Si3N4-SiC particulate composites

High resolution transmission electron microscope observations of grain boun daries in hexagonal boron nitride in which adjacent grains are rotated with respect to one another about either <2 (1) over bar (1) over bar 0> or <10 (1) over bar 0> directions are shown to be free of intergranular glass, in agreement with previous work. The implication of these observations is tha t the solid-solid boundary energies of such grain boundaries in hexagonal b oron nitride are relatively small in magnitude.