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A. M. Cardinale et al.
Table 3 Lattice parameters of the ternary compounds of the Nd–Al–Si system (this work)
Compound
Crystal structure
Lattice parameters/nm
a
b
c
s1 NdAl2Si2
hP5-CaLa2O2
hP3-AlB2
0.4212
0.4276
0.4199
0.4107
0.4442
0.6702
0.4204
1.4410
0.4286
0.4043
s2 Nd2Al3Si
s3 NdAl(1-x)Si(1?x), x = *0
s4 Nd4Al3Si3
tI12-aThSi2
oS20-Pr4Al3Ge3
oS8-CrB
2.5987
1.1131
s5 Nd2Al(1-x)Si(1?x), x = 0.25
compounds with the third element amount of less than 1 at.%
were not taken into account.
about 50 ternary alloys. The three-phase fields and the two-
phase fields shown in the isothermal section are 22 and 13,
respectively.
According to the literature data, the two compounds
Nd2Si3 and Nd3Si4 exist in the 55–67 at.% Si. To confirm
these compounds, we prepared a few binary Nd–Si samples
close to the 2:3 and 3:4 stoichiometric ratios. Only the Nd2Si3
was found; samples with compositions close to 57 at.% Si
always gave a mixture of NdSi and Nd2Si3. DTA performed
on a sample corresponding to the Nd41.5Si58.5 composition
highlighted a thermal effect at 530 ꢀC that is the allotropic
transformation of this phase.
The following ternary phases were found to exist:
•
•
The crystal structure of the stoichiometric phases
NdAl2Si2 (s1), hP5-CaLa2O2 and Nd2Al3Si (s2), hP3
AlB2 were confirmed.
The two phases NdAl1-xSi1?x (s3), tI12-aThSi2 and
Nd2Al1-xSi1?x (s, oS8-CrB type extend, at Nd content
constant (33.3 and 50), at 25–40 at.% Si and
20–25 at.% Si, respectively.
A number of ternary phases were found in the Nd–Al–Si
isothermal section. Their crystal structure and lattice
parameters are reported in Table 3.
•
The new ternary phase Nd4Al3Si3 (s4) is proposed to be
isostructural with Pr4Al3Ge3, oS20-Pr4Al3Ge3 type.
The stoichiometric NdAl2Si2 (s1) phase was confirmed
to crystallize in the hP5-CaLa2O2 type structure.
Two phases have been found along the 33.3 at.% Nd:
the stoichiometric Nd2Al3Si (s2) phase and NdAl1-xSi1?x
(s3) phase existing in a wide homogeneity range (*25–40
at.% Si). This is in contrast with what was previously
reported in the literature for this phase where a homoge-
neity range from 20 to 50 at.% Si has been suggested [12].
DTA performed on s3 samples with a composition corre-
sponding to x = 0 (NdAlSi) indicate a melting temperature
of 1,440 ꢀC. The micrographic features of the same sam-
ples suggest a congruent melting formation for s3.
The stoichiometric Nd4Al3Si3 (s4) phase was not pre-
viously reported in the literature. However, phases with the
same stoichiometry were found in a number of R–Al–Ge
systems (R = La, Ce, Pr, Nd, Sm). The s4 phase crystal-
lizes orthorhombic, isostructural with Pr4Al3Ge3.
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123