DETERMINATION OF GRAIN-BOUNDARY VOLUME EXPANSION BY HREM

High resolution electron microscopy (HREM) has provided invaluable ins ight into the structure of grain boundaries at the atomistic level. Qu antitative HREM methods are now in development which, combined with at omistic simulations, can provide further insight into grain boundary s tructure-energy correlations. For example, the volume expansion (or ex cess free volume, delta), a thermodynamic parameter directly related t o the grain boundary energy, is represented by the normal component of the rigid body translation. Although its magnitude is small, it can b e determined experimentally using statistical techniques which locate and fit the peak and valley positions in an experimental HREM image, i .e., a direct measurement of the lattice fringe displacements is made. We have modified the lattice fringe displacement technique such that a measurement accuracy of better than +/- 0.002a(0) can be achieved. P recise knowledge of the position and intensity of the image contrast a nd a detailed understanding of the sources of error are required. This paper provides a detailed description of the lattice fringe displacem ent technique as well as a detailed assessment of the sources of error in the measurement.