1. L E Toth,Transition metal carbides and nitrides (Academic Press, New York, 1971)
2. H Bilz and W Kress,Springer series in solid state sciences 10, 1 (1979)
3. R K Singh and H N Gupta,Solid State Commun. 16, 197 (1975)
4. R K Singh,Phys. Reports (Netherlands)85, 259 (1982)
5. L Pinschovius, W Reichardt and B Scheeres,J. Phys. C11, 1557 (1978)