Electronic Structure and Mechanical Properties of Grain Boundaries

Our ab-initio quantum mechanical calculations on grain boundaries have progressed beautifully. We have succeeded in obtaining some interesting and new results for both clean and doped gain boundary systems. In particular we find the following. For the clean Germanium sigma 5 310 tilt boundary the ideal atomic configuration is as shown at the top of Fig. 1. Here we are looking along the 130 axis. The 310 grain boundary plane is perpendicular to the plane of the figure and passes through the atoms represented by unfilled circles. The horizontal direction is 001. On either side of the boundary plane we see atoms from the two grains, filled circles on the bottom and shadowed circles on the top. Note that the atoms with unfilled circles which are in the immediate vicinity of the boundary form strange-looking bonds with neighboring atoms. One can even see a three-fold ring of bonds right at the interface.