EXPERIMENTAL AND THEORETICAL-STUDIES OF SCS UNDER PRESSURE

The compressibilities of ScS and a series of Sc1-xS metal defect struc tures (x > 0) were studied using a diamond anvil cell and synchrotron radiation at pressures up to 73 GPa. The results show that the bulk mo dulus increases with x, in contrast to the usual view that a less dens e material is more easily compressed. The results are in qualitative a greement with existing band structure calculations designed to probe t he mechanism of the ready metal atom loss from ScS at high temperature s. They are also in agreement with new calculations, both of the tight -binding and the first-principles FLAPW type. Numerically the latter s how an increase in the bulk modulus of 30% between ScS and Sc0.875S an d are in exact numerical agreement with the experimental results.