Critical observations in the research of carbon nitride

SL critical view on the research of carbon nitride (CNx) with an emphasis o n the predicted alpha- and beta -C3N4 phases derived from their Si3N4 analo gues is presented. This paper highlights the reasons for the less occurence of planar nitrogen in both phases which otherwise presumed to be existed a s in their silicon nitride counterparts which to date, has not been searche d and reported appropriately. Also, other hypothetical C3N4 phases includin g the very recently predicted spinel phase, c-C3N4 are discussed. Further, the recent synthesis of carbon nitrides and their characterisations are bri efly reviewed. Finally, an outlook is presented which includes most promisi ng synthesis routes for crystalline carbon nitride. (C) 2000 Elsevier Scien ce S.A. All rights reserved.