X-ray powder diffraction refinement of Ag2In2SiSe6 structure and phase diagram of the AgInSe2-SiSe2 system

The phase diagram of the AgInSe2-SiSe2 system was investigated using the results of differential thermal analysis and X-ray diffraction. The existence of a new quaternary phase, Ag2In2SiSe6, was discovered in the system; it melts congruently at 1100 K and has a polymorphous transition at 1040 K. The crystal structure of the low-temperature (LT) modification of this phase was investigated using powder X-ray diffraction. Ag2In2SiSe6 crystallizes in a monoclinic structure, space group (S.G.) Cc (structural type Ag2In2GeSe6), with lattice parameters a = 1.26683(4) nm, b = 0.74565(3) nm, c = 1.26133(4) nm and β = 109.286(2)°. The atomic parameters were refined in the isotropic approximation to RI = 0.0758 and RP = 0.1096.