CHEMICAL BONDING STATE OF PHOSPHORUS ATOM TO IRON ATOM AT GRAIN BOUNDARY OF IRON AND IN Fe//3P CRYSTAL.

Phosphorus at grain boundary of iron is known to be in similar bonding state to that in Fe//3P crystal. In order to obtain information on the chemical bonding state of phosphorus to iron at grain boundary, valence electron population analysis of X-ray diffraction data and theoretical bandstructure calculation have been performed for Fe//3P crystal. The observed effective charges of the atoms are consistent with the calculated charge distributions. A covalent bonding state between Fe 3d and P 3p states occurs on the density of states. At grain boundary where the interaction between phosphorus atoms is two-dimensional, the covalent bonding state between iron and phosphorus atoms is inferred from the results for Fe//3P. It is proposed that the decohesion of the boundary might be initiated at the transient interface between the covalent bonding state and the metallic state in the matrix.