Crystal Structure of Chalcogenides R′xRyR′zPbSi2S8 (R′ - La, R - Tb, R′ - Er)

The LaxTbyErzPbSi2S8 chalcogenides were obtained by synthesizing the elementary components in vacuum quartz containers at 1320 K. The synthesized alloys were homogenized by annealing at 770 K during 500 hours. The cell parameters of synthesized sulfides are: a = 0.89576(3) nm, c = 2.65646(8) nm - La1.2Tb0.4Er0.4PbSi2S8; a = 0.89209(1) nm, c = 2.63466(5) nm - La0.9Tb0.2Er0.9PbSi2S8; a = 0.89002(3) nm, c = 2.62714(7) nm - La0.67Tb0.67Er0.67PbSi2S8; a = 0.88993(1) nm, c = 2.62973(4) nm - La0.6Tb1.2Er0.2PbSi2S8; a = 0.885161(7) nm, c = 2.60445(3) nm - La0.2Tb0.9Er0.9PbSi2S8 respectively. The statistical mixture of (La, Tb, Er, Pb) atoms occupy 18e site (x y 1/4), and Si atoms occupy 12c site (1/3 2/3 z) in the structure of the obtained chalcogenides. Coordinating polyhedra of the statistical mixture (La, Tb, Er, Pb) atoms are trigonal prism with two additional atoms (CN = 8), and the Si atoms occupy the crystallographic point system 12c described with the tetrahedron. According to the experimental results, the synthesized chalcogenides crystallize in the La2PbSi2S8 structure type (hR26,167). The structure of La2PbSi2S8 is described by using the theory of second anion coordination (SAC).

Automated summary

The chalcogenides La2TbErPbSi2S8 were obtained by synthesizing elementary components in vacuum containers and annealing at 770K, with statistical mixture of (La, Tb, Er, Pb) atoms and Si atoms occupying different sites in the structure. The experimental results showed that the synthesized chalcogenides crystallize in the La2PbSi2S8 structure type.