X-ray powder diffraction refinement of Ag_2In_2SiSe_6 structure and phase diagram of the AgInSe_2-SiSe_2 system

摘要

The phase diagram of the AgInSe_2-SiSe_2 system was investigated using the results of differential thermal analysis and X-ray diffraction. The existence of a new quaternary phase, Ag_2In_2SiSe_6, was discovered in the system; it melts congruently at HOOK 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. Ag_2In_2SiSe_6 crystallizes in a monoclinic structure, space group (S.G.) Cc (structural type Ag_2In_2GeSe_6), with lattice parameters a = 1.26683(4) nm, b = 0.74565(3) nm, c = 1.26133(4) nm and beta = 109.286(2) deg. The atomic parameters were refined in the isotropic approximation to R_I = 0.0758 and R_P = 0.1096.