The quasi-ternary system La₂S₃–Er₂S₃–Ga₂S₃ and quaternary compounds of the composition La(Pr)_1.5Tb(Y, Ho)_1.5Ga_1.67S₇

Chem. Met. Alloys 9 (2016) 105-112

https://doi.org/10.30970/cma9.0337

Inna IVASHCHENKO, Iryna DANYLIUK, Lubomir GULAY, Volodymyr HALYAN, Petro TISHCHENKO, Ivan OLEKSEYUK

The isothermal section of the La₂S₃–Er₂S₃–Ga₂S₃ system at 770 K was investigated by XRD. La₃Ga_1.67S₇ forms a solid solution range extending to 50 mol.% “Er₃Ga_1.67S₇”, i.e. La_1.5Er_1.5Ga_1.67S₇ is the boundary composition of this solid solution. The unit cell parameters vary linearly from a = 1.0180(4) nm, c = 0.6055(2) nm for La₃Ga_1.67S₇ to a = 0.9820(5) nm, c = 0.6228(3) nm for the sample of composition 27 mol.% La₂S₃ – 37 mol.% Er₂S₃ – 36 mol.% Ga₂S₃ (50 mol.% “Er₃Ga_1.67S₇”). The crystal structures of La_1.5Y_1.5Ga_1.67S₇, Pr_1.5Tb_1.5Ga_1.67S₇, and Pr_1.5Ho_1.5Ga_1.67S₇ were determined by powder XRD; they belong to the structure type Ce₃Al_1.67S₇, space group P6₃. A continuous solid solution series (CSSS) with this hexagonal structure was observed in the quasi-ternary system La₂S₃–Tb₂S₃–Ga₂S₃ along the concentration line 36 mol.% Ga₂S₃. The unit cell parameters vary from а = 0.9670(3) nm, с = 0.6083(2) nm for Tb₃Ga_1.67S₇ to a = 1.0180(4) nm, c = 0.6055(2) nm for La₃Ga_1.67S₇, with the с-parameter having a maximum at the composition La_1.5Tb_1.5Ga_1.67S₇.

Polyhedral representation of the crystal structure of La_1.5Tb_1.5Ga_1.67S_7.

Keywords

Rare-earth metals / Phase equilibria / Crystal structure / Chalcogenides / X-ray powder diffraction