Research on carbon nitrides

The status of research on carbon nitride compounds is reviewed including exciting recent results. On the basis of the early theoretical predictions by Cohen and co-workers in 1985-1990, covalent carbon nitrides should be as hard as diamond. The high hardness, high wear resistance and low coefficient of friction make it attractive for industrial operation. The various empirical and nb initio theoretical results are summarized. Attention is paid to him synthesis techniques and crystal characterizations, such as chemical, structural, electrical, optical, thermal and mechanical properties. New carbon nitride structures and selected-phase growth are also described. Finally, some major outstanding problems facing carbon nitride researchers are identified, and some important problems, which should be addressed in the near future, are suggested. (C) 1998 Elsevier Science Ltd