Liquid Ga was used as a solvent to explore the phase formation between rare-earth metals
(REs), Ni, and a tetrelide (Tt = Si, Ge). The reactions were performed in excess liquid Ga at
850 °C. Two new phases of general formulas RE0.67Ni2Ga5
-
x
Tt
x
and RE0.67Ni2Ga6
-
x
Tt
x
were
found and structurally characterized. The Co analogues of the latter RE0.67Co2Ga6
-
x
Ge
x
(RE
= Y, Gd) were also prepared. Single-crystal X-ray data: The first group of compounds
RE0.67Ni2Ga5
-
x
Tt
x
crystallizes in the hexagonal space group P63/mmc with a structure related
to the RE2
-
x
Pt4Ga8+
y
type (Sm0.53Ni2Ga5
-
x
Ge
x
, a = 4.1748(7) Å, c = 16.007(4) Å, V = 241.61(8)
Å3, Z = 2; Y0.59Ni2Ga5
-
x
Ge
x
, a = 4.1344(11) Å, c = 15.887(6) Å, V = 235.18(12) Å3, Z = 2;
Tb0.67Ni2Ga5
-
x
Si
x
, a = 4.1415(11) Å, c = 15.843(6) Å, V = 235.33(12) Å3, Z = 2; Ho0.67Ni2Ga5
-
x
Ge
x
,
a = 4.1491(4) Å, c = 15.877(2) Å, V = 236.71(5) Å3, Z = 2). The second group RE0.67Ni2Ga6
-
x
Tt
x
crystallizes in P6̄m2 (Gd0.67Ni2Ga6
-
x
Ge
x
, a = 4.1856(10) Å, c = 9.167(3) Å, V = 139.08(7) Å3,
Z = 1; Sm0.67Ni2Ga6
-
x
Si
x
, a = 4.1976(8) Å, c = 9.159(3) Å, V = 139.76(5) Å3, Z = 1) in a
structure related to the ErNi3Al9 structure type with disorder in the RE−Ga plane.
Dy0.67Ni2Ga6
-
x
Ge
x
crystallizes in space group P3̄1c (a = 7.2536(8) Å, c = 18.308(3) Å, V =
834.21(2) Å3, Z = 6) with partial disorder in the RE−Ga plane. The structures of these two
groups of compounds are related to each other and contain similar building motifs, namely
Ga
n
[NiGa2
-
x
/2Ge
x
/2]2 slabs and RE0.67Ga monatomic layers which alternate along the c-direction, forming a 3D structure. The parameter x and the position of the tetrelide in the
structure were determined by single-crystal neutron diffraction. Complete or partial disorder
of the RE and Ga atoms is observed in the RE−Ga plane. The origin of the disorder lies in
the extensive and random stacking faults of ordered RE−Ga planes, which apparently slide
easily in the ab plane and create an averaged disordered picture. Electrical conductivity
and thermopower measurements indicate that these compounds are metallic conductors.
The magnetic measurements show antiferromagnetic ordering at ∼3−4 K and Curie−Weiss
behavior at higher temperatures with the values of μeff close to those of RE3+ free ions. Strong
2-fold crystal field anisotropy is observed for the heavy RE analogues. The anisotropy constants K
2
para calculated from the Weiss constant anisotropy for heavy RE analogues are
reported.
