The influence of grain boundaries on local electronic states and the distribution of 57Fe ions in c-BN polycrystals was investigated as a function of processing. The study was performed on 2 sets of c-BN samples. One was prepared by catalytic synthesis, and the other was synthesized by direct phase transformation. It was established that, under catalytic synthesis, Fe ions were predominantly incorporated into the c-BN grain bulk in the Fe3+ charge state. But after direct phase transformation, Fe ions were distributed mainly along grain boundaries in the Fe2+ state; due probably to the enhanced grain-boundary diffusion of Fe. The suppression of Fe grain-boundary diffusion, and its incorporation mainly into the grain bulk, under catalytic synthesis could be attributed to interlocking of the movement of Fe ions by the precipitation of nitrides and borides of catalytic impurities (Al and Si) which formed along the grain boundaries during c-BN synthesis.

Effect of Grain Boundaries on Iron Distribution in Polycrystalline Cubic Boron Nitride. J.A.Fedotova, A.K.Fedotov, N.A.Shishonok, J.Stanek: Journal of Physics - Condensed Matter, 2002, 14[48], 12855-63