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International audienceX-ray diffraction measurements on MnGa2Se4, a II-III2-VI4 magnetic semiconductor compound, are made as a function of pressure up to 25 GPa. It is found that in the range of 0P12 GPa the structure is a defect tetragonal; in the range between 12 and 14 GPa a two phase field +NaCl type exists. It is found that at about 14 GPa a transition to the cubic NaCl-type structure occurs and it appeared that this transition is irreversible. From the analysis of the x-ray diffraction lines, lattice parameter values are determined as a function of pressure. These results allow the evaluation of the compressibility coefficients of the corresponding parameters. The observed behavior of , a, and c with pressure are explained by using the relations proposed by Abrahams and Bernstein J. Chem. Phys. 52, 5607 1970. It is found that at about 3 GPa, a symmetry change, from an ordered tetragonal to a disordered tetragonal structure, occur

X-ray powder diffraction measurements and differential thermal analysis (DTA) were made on polycrystalline samples of the Cu 2 Cd 1−z Mn z GeSe 4 and Cu 2 Cd 1−z Fe z GeSe 4 alloy systems. The diffraction patterns were used to show the equilibrium conditions and to derive lattice parameter values. The effect of the annealing temperature and cooling rate to room temperature are discussed. For the Cu 2 Cd 1−z Fe z GeSe 4 system, only two single solid phase fields, the tetragonal stannite ␣ and the wurtz-stannite ␦ structures were found to occur in the diagram. For the Cu 2 Cd 1−z Mn z GeSe 4 system, in addition to the tetragonal stannite ␣ and the wurtz-stannite ␦ phases, MnSe was found to exist in the diagram. The DTA experiments showed that the cooling curves for both systems exhibited effects of undercooling.

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