The quasi-ternary system La2S3–Er2S3–Ga2S3
and quaternary compounds of the composition La(Pr)1.5Tb(Y, Ho)1.5Ga1.67S7
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. La3Ga1.67S7
forms a solid solution range extending to 50 mol.% “Er3Ga1.67S7”,
i.e. La1.5Er1.5Ga1.67S7 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 La3Ga1.67S7
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.% “Er3Ga1.67S7”). The crystal
structures of La1.5Y1.5Ga1.67S7, Pr1.5Tb1.5Ga1.67S7,
and Pr1.5Ho1.5Ga1.67S7 were
determined by powder XRD; they belong to the structure type Ce3Al1.67S7, 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 à = 0.9670(3) nm,
ñ = 0.6083(2) nm for
Tb3Ga1.67S7 to a = 1.0180(4) nm, c = 0.6055(2) nm for La3Ga1.67S7,
with the ñ-parameter having a maximum
at the composition La1.5Tb1.5Ga1.67S7.
Polyhedral
representation of the crystal structure of La1.5Tb1.5Ga1.67S7.
Keywords
Rare-earth metals /
Phase equilibria /