Synthesis and crysal structure of selenides R3Ag4kGe1.25-kSe7 (R – La, Ce; k = 0.05; 0.10; 0.15)
DOI:
https://doi.org/10.15330/pcss.26.4.752-759Keywords:
crystal structure, rare earth elements, quaternary non-centrosymmetric selenides, X-ray powder methodAbstract
The paper presents the results of the study of the crystal structure of six selenides of the composition R3Ag4kGe1.25-kSe7 (R – La, Ce; k = 0.05; 0.10; 0.15) as promising materials for use in various semiconductor technologies. Due to their potentially interesting nonlinear optical, magnetic and electrical properties, as well as other unique characteristics, these selenides can find application in scientific research and engineering developments, which opens up opportunities for the creation of modern materials with new functional properties.
The crystal structure of the selenides La3Ag0.20Ge1.20Se7 (А) [a = 10.779(1) Å, c = 6.0876(8) Å, RI = 0.0982, RP = 0.2544], La3Ag0.40Ge1.15Se7 (B) [a = 10.7821(9) Å, c = 6.0927(7) Å, RI = 0.0950, RP = 0.2377], La3Ag0.60Ge1.10Se7 (C) [a = 10.7977(5) Å, c = 6.0997(5) Å, RI = 0.0920, RP = 0.2156], Ce3Ag0.20Ge1.20Se7 (D) [a = 10.6948(5) Å, c = 6.0635(6) Å, RI = 0.1130, RP = 0.2649], Ce3Ag0.40Ge1.15Se7 (E) [a = 10.7074(6) Å, c = 6.0697(7) Å, RI = 0.0977, RP = 0.2529] and Ce3Ag0.60Ge1.10Se7 (F) [a = 10.7147(4) Å, c = 6.0729(4) Å, RI = 0.0985, RP = 0.2100] was studied by powder X-ray diffraction. The structure is represented by various geometric units, trigonal prisms with two additional atoms [R 8Se], tetrahedra [Ge 4Se], and monohedra [M 3Se]. These structural elements indicate a complex structure of selenides, which includes various types of chemical bonds and interactions between atoms in the crystal lattice.
The synthesized selenides crystallize in the hexagonal symmetry (La3CuSiS7 structure type; space group P63; Pearson symbol hP24,173). La or Ce atoms are localized in the 6c site (x y z), atoms of the statistical mixtures M(Ag + Ge) in the 2a site (0 0 z), and Ge atoms are in the 2b site (1/3 2/3 z). Selenium in the crystal lattice has three atomic sites, Se1 (2b site), Se2 and Se3 (6c site). The primitive hexagonal unit cell contains two
La(Ce)3Ag4kGe1.25-kSe7 formula units. The trigonal prisms [R 8Se] are connected by edges and form “blocks” of three prisms in each. The [R(Ag + Ge) 6Se] octahedra have common faces and form “columns” in the direction of the main axis. Trigonal prisms and octahedra form common faces. The [Ge 4Se] tetrahedra are isolated from each other.
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