Investigation of the chemical reactivity and stability of c-BNP

Bulk material of cubic boron nitride (c-BN) is commercially achieved via hi gh pressure-high temperature (HPHT) synthesis from h-BN with various cataly sts (flux precursors). Since recent investigations indicated c-BN to be the stable modification at standard conditions there is considerable interest to realise a c-BN synthesis at normal or low pressure. Thus growth conditio ns allowing high mobility for boron and nitrogen atoms have to be found. The interaction of c-BN with various flux precursors used under HPHT condit ions was investigated up to 1300 degrees C at ambient pressure. The reagent s were chosen with regard to their ability to stabilize intermediate reacti on products. Metals, nitrides and fluorides were applied for the chemical a ttack. The morphological changes and degradation of the c-BN crystals were examined by scanning electron microscopy (SEM), X-ray diffraction and infra red spectroscopy. SEM studies indicate that the degradation of c-BN depends strongly on the nature of the flux precursors. Those leading to an interme diate phase during the reaction exhibit distinct etching figures on (111)-p lanes of c-BN, while reagents leading to the formation of several products cause an inhomogeneous decay. Since the degradation of c-BN resembles the r eversed growth, the reaction mechanism of the interaction of c-BN with reac tive melts allows to establish a growth and degradation model of the cubic phase. The results shall help finding new routes to grow c-BN in a low pres sure-melt or chemical vapour deposition process. (C) 1999 Elsevier Science S.A. All rights reserved.