Charge states and distribution of iron ions in polycrystalline cubic boron nitride

Abstract

The local electronic states and distribution of 57Fe ions in cubic boron nitride (c-BN) polycrystals as a function of technological processing were investigated. The study has been performed on c-BN samples prepared by catalytic synthesis and by direct phase transformation. It was established that in catalytically synthesised c-BN iron ions are predominantly incorporated into the grain bulk in Fe3+ charge state. In the contrary, in c-BN manufactured by direct phase transformation Fe ions are distributed mainly along the grain boundaries in Fe2+ state probably due to the enhanced grain boundary diffusion of iron. Suppression of grain boundary diffusion of Fe ions (and their predominant incorporation into the grain bulk) under catalytic synthesis was ascribed to interlocking of Fe ions movement by precipitation of nitrides and borides of catalytic impurities (Al and Si) nucleated at the grain boundaries during c-BN synthesis.