Zn,+Mg,Se mixed crystals were grown by the high-pressure Bridgman method in the x range 0.06 to 0.285. X-ray investigations show that with increasing Mg content the transition from a sphalerite structure to wurtzite occurs at x = 0.185 4 0.03. After annealing in liquid zinc or zinc vapour, investigated crystals exhibit n-type conductivity as well as blue-violet and orange photoluminescence in the temperature range from 40 K to room temperature.

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The electronic structure of Ni3 Al1-x Fex ordered alloys was calculated using the ab initio self-consistent linear muffin-tin orbital method with the local density approximation. Two models of the preference in the site occupancy at the elemental cell were considered: (i) the Fe atoms substitute the Al atoms located at the corners of the fcc cube; (ii) the Fe atoms substitute the Ni atoms located at the faces of the cube and the appropriate number of Ni atoms is located at the cube corners. Changes in the `raw' density of states distribution (DOS) for these two models were discussed and compared with the x-ray spectra. The magnetic moments calculated for the first model resemble the experimental data more than those calculated for the second one. The DOS distributions were calculated over a wide energy range in the valence as well as in the conduction band and projected on the constituent atoms separately for different symmetries of states. Such an approach allowed us to compare predictions of the theory with the appropriate x-ray spectra. In all collected x-ray spectra, one can find changes of characteristic features consistent with the changes observed in the calculated DOS under the assumption of the first model of site occupancy. The one-electron model was utilized in the spectrum interpretation. The performed studies indicated that it is the first model of Fe substitution that finds confirmation in the magnetic and x-ray investigations.