NON-CENTROSYMMETRIC SELENIDES R3Ag0.45Ga1.52Se7 (R – La, Ce, Pr AND Nd)
DOI:
https://doi.org/10.32782/pcsd-2025-1-1Keywords:
rare earth metals, selenides, crystal structure, X-ray powder method, EDAX-analysisAbstract
Selenides of the composition R3Ag0.45Ga1.52Se7 (R = La, Ce, Pr and Nd) were obtained by sintering the elementary components in evacuated quartz containers at 1320 K, with homogenizing annealing of the alloys at 770 K for 500 hours. The crystal structure of the selenides La3Ag0.45Ga1.52Se7 (a = 10.5959(5) Å, c = 6.3684(5) Å, RI = 0.0912, Rp = 0.2155), Ce3Ag0.45Ga1.52Se7 (a = 10.4484(10) Å, c = 6.3489(8) Å, RI = 0.0998, Rp = 0.2363), Pr3Ag0.45Ga1.52Se7 (a = 10.4419(9) Å, c = 6.3747(7) Å, RI = 0.0855, Rp = 0.1740) and Nd3Ag0.45Ga1.52Se7 (a = 10.3059(5) Å, c = 6.3798(5) Å, RI = 0.0996, Rp = 0.2174) was studied by powder diffractometry. Their structure belongs to the structural type La3CuSiS7 (SG P63; SP hP24). The rare-earth atoms in this structure are located in the 6c site (x y z) and center trigonal prisms of selenium atoms with one additional atom [R 3Se13Se21Se3] (CN = 7). Ga atoms occupy the 2a site (0 0 z) and center octahedra of selenium atoms (CN = 6). The atoms of the statistical mixtures M(0.450Ag + 0.520Ga) are localized in the 2b site (1/3 2/3 z) and have tetrahedral environment of selenium atoms [Ga Se13Se3] (CN = 4). Selenium in the crystal lattice has three atomic positions, Se1, Se2 (6c site) and Se3 (2b site). Trigonal prisms with one additional atom form blocks 3[R 7Se] where the trigonal prisms are interconnected by edges. The Ga-centered octahedra are interconnected by faces and form infinite columns [Ga 6Se]n in the direction of the c axis. Trigonal prisms form common faces with octahedra. The [M 4Se] tetrahedra are isolated from each other, a decrease in the unit cell parameters is observed in the La–Ce–Pr–Nd series due to the size factor of the rare earth elements. Obtained selenides can be used as promising materials for nonlinear optics due to the non-centrosymmetric structure.
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