The system Ag2Se–Ho2Se3 in the 0–50 mol.% Ho2Se3 range and the crystal structure of two polymorphic forms of AgHoSe2

The phase diagram of the Ag2Se–Ho2Se3 system in the range of 0–50 mol.% Ho2Se3 was constructed with the results of XRD and differential thermal analysis. A dimorphous compound exists in the system at the equimolar ratio of the components. The investigated part of the Ag2Se–AgHoSe2 diagram is of the eutectic type with the eutectic coordinates 7 mol.% Ho2Se3 and 1125 K. The crystal structure of the high-temperature modification of AgHoSe2 was studied by X-ray powder diffraction method. α-AgHoSe2 is described as a NaCl structure (space group F m 3 ¯ m ) with the lattice parameter а = 5.7623(3) Å. Atomic parameters were calculated in the isotropic approximation (RI = 0.0434 and RР = 0.0636). The crystal structure of β-AgHoSe2 was determined by X-ray structure analysis and was refined to R = 0.0487.