Phase equilibria in the Ag4SSe-As2Se3 system

The phase diagram of the system Ag4SSe-As2Se3 is studied by means of X-ray diffraction, differential thermal analyses and measurements of the microhardness and the density of the materials. The unit-cell parameters of the intermediate phases 3Ag(4)SSe center dot As2Se3 (phase A) and Ag4SSe center dot 2As(2)Se(3) (phase B) are determined as follows for phase A: a=4.495 angstrom, b=3.990 angstrom, c=4.042 angstrom, alpha=89.05 degrees, beta=108.98 degrees, gamma=92.93 degrees; for phase B: a=4.463 angstrom, b=4.136 angstrom, c=3.752 angstrom, alpha=118.60 degrees, beta=104.46 degrees, gamma=83.14 degrees. The phase 3Ag(4)SSe center dot As2Se3 and Ag4SSe center dot 2As(2)Se(3) have a polymorphic transition alpha <->beta consequently at 105 and 120 degrees C. The phase A melts incongruently at 390 degrees C and phase B congruently at the same temperature.