HARDNESS OF CRYSTALS WITH NACL STRUCTURE AND THE SIGNIFICANCE OF THE GILMAN-CHIN PARAMETER

The microhardness of PbTe, PbSe, EuS and EuSe has been determined. The microhardness vs lattice constant plot for chalcogenides is a curve s imilar to the one for alkali halides. The Gilman-Chin parameter (H/C-4 4) has been calculated for a large number of crytals with NaCl structu re. There is no unique value representing the entire group of crystals , the values ranging from 0.01 to 0.20. The Gilman-Chin parameter broa dly correlates with the effective ionic charge (e) indicating that it is a measure of the ionicity. Empirically, it is observed that the pr oduct (H/C-44).(e)(2) is approximately constant.