CRYSTAL STRUCTURE OF THE Pr3Ag4xGe1,25-xSe7 (x = 0,10; 0,15)

The samples of composition Pr3Ag4xGe1,25-xSe7 (x = 0,10; 0,15), weighing one gram, obtained by sintering elementary components in vacuumed quartz containers at a maximum temperature of 1150 °C. The diffraction patterns for X‑ray phase analysis were recorded at a DRON4–13 diffractometer for 2Q range of 10–100 ° (CuKα radiation, scan step 0,02 °, 20 s exposure in each point). For data processing and the determination of the  crystal structure used WinCSD software package. Visualization of the crystal structure, stacking and coordination polyhedra was performed using VESTA  program. The crystal structure of the quaternary compound Pr3Ag0,40Ge1,15Se7 (a = 1,06466(4) nm, с = 0,60552(3)  nm, RI = 0,0511, Rp = 0,2455) and Pr3Ag0,60Ge1,10Se7 (a = 1,06556(2) nm, c = 0,60583(2) nm, RI = 0,0618, Rp = 0,2068) was investigated by powder X‑ray method.  The structure of the compound belongs to the  La3CuSiS7 structural type (space group P63, Pearsoncode hP24, a = 1,028 nm, c = 0,575 nm). In this structure, the Pr atom is located in the 6c site and, together with selenium atoms, form trigonal prisms with two additional atoms [Pr Se14Se23Se3] (CN = 8). The atoms of the statistical mixture M1 (0,15 Ge + 0,40 Ag) and M2 (0,10 Ge + 0,60 Ag) occupying one site 2a are located in triangles [M 3Se2] (CN = 3). The Ge atoms are localized in site 2b and have a tetrahedral surrounding of Selenium atoms [Gе Se13Se3] (CN = 4). Atoms Se1 (site 2b) and Se3 (site 6c) also have a tetrahedral surrounding. Se2 atoms (site 6c) are surrounded by five neighbors. Inter-atomic distances are consistent with the sum of the respective ionic radii. Germanium-containing Pr3Ag0,40Ge1,15Se7 and Pr3Ag0,60Ge1,10Se7 selenides based on praseodymium are promising chalcogenide phases on the basis of which materials for nonlinear optics can be created.