The 673 K isothermal section of the La-Ni-Sn ternary system

Article abstract of DOI:10.1016/S0925-8388(03)00475-4

The phase relationships in the La-Ni-Sn ternary system at 673 K have been investigated by means of X-ray powder diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Most of this ternary system was studied at 673 K. At this temperature, a new ternary compound whose atomic ratio is close to La/Ni/Sn = 1:1:3 has been found. The existences of 15 binary compounds La ₇Ni₃, LaNi, La₂Ni₃, La ₇Ni₁₆, LaNi₃, La₂Ni₇, LaNi₅, Ni₃Sn, Ni₃Sn₂, Ni ₃Sn₄, La₅Sn₃, La₅Sn ₄, LaSn, La₃Sn₅, LaSn₃ and seven other ternary compounds LaNi₅Sn, LaNi₄Sn₂, LaNi₂Sn₂, La₃Ni₂Sn₆, La₃Ni₂Sn₇, La₃Ni₈Sn ₁₆, LaNiSn have been confirmed too. There are 31 three-phase regions in the 673 K isothermal section. Due to the lower melting point of Sn (about 504 K), a small part of the ternary system that lies in the Sn-rich part was studied at 483 K.

Full text of DOI:10.1016/S0925-8388(03)00475-4

Journal of Alloys and Compounds 363 (2004) 223–226
The 673 K isothermal section of the La–Ni–Sn ternary system
∗
Yinghong Zhuang , Haixia Deng, Jingqi Liu, Qingrong Yao
Institute of Materials Science, Guangxi University Nanning, 530004, PR China
Received 3 February 2003; received in revised form 28 April 2003; accepted 28 April 2003
Abstract
The phase relationships in the La–Ni–Sn ternary system at 673 K have been investigated by means of X-ray powder diffraction (XRD),
differential thermal analysis (DTA), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Most of this ternary
system was studied at 673 K. At this temperature, a new ternary compound whose atomic ratio is close to La/Ni/Sn = 1:1:3 has been found.
The existences of 15 binary compounds La
7
Ni
3
, LaNi, La
2
Ni
3
, La
7
Ni16, LaNi
3
, La
2
Ni
7
, LaNi
5
, Ni
3
Sn, Ni
Ni
3
Sn
Sn
2
, Ni
, La
3
Sn
Ni
4
, La
5 3 5 4
Sn , La Sn , LaSn,
La Sn , LaSn
3
5
3
and seven other ternary compounds LaNi
5
Sn, LaNi
4
Sn , LaNi
2
2
Sn
2
, La
3
Ni Sn
2
6
, La
3
2
7
3
8
Sn16, LaNiSn have been
confirmed too. There are 31 three-phase regions in the 673 K isothermal section. Due to the lower melting point of Sn (about 504 K), a small
part of the ternary system that lies in the Sn-rich part was studied at 483 K.
©
2003 Elsevier B.V. All rights reserved.
Keywords: Rare earth compounds; Transition metal compounds; Phase diagram; Crystal structure; X-Ray diffraction
1
. Introduction
given in Table 1. Seven ternary compounds in the La–Ni–Sn
system were found in Ref. [8] and their structural data are
given in Table 2 (the structural data for the newly found
ternary compounds are being studied and we will report
them in a later article).
Rare earth AB5 Haucke phase [1] alloys are being
used extensively in negative electrodes of rechargeable
nickel–metal hydride (Ni–MH) batteries. Among all these
alloys, LaNi -based alloys are promising negative electrodes
All these results have shown that the phase relationships in
the La–Ni–Sn ternary system are well worth studying com-
pletely in order to provide valuable information for improv-
ing material properties and developing new materials. Up to
now, the phase diagram of the La–Ni–Sn ternary system has
not been reported. In this paper, we studied the isothermal
section of the La–Ni–Sn ternary system mainly at 673 K.
5
because they have high capacity, high charge discharge
ability when they store hydrogen and can be activated eas-
ily. There are some studies reporting that the substitution of
a small amount of Sn for Ni in LaNi alloys can improve
5
the property and hydrogen storage ability of LaNi alloys
5
[12–14]. Moreover, as reported, some ternary compounds in
the La–Ni–Sn system have interesting magnetic properties
and magnetic resistances, such as LaNiSn, LaNi4Sn2 and
LaNi2Sn2 [18–20]. Although a great deal of investigation
has been done, there is some inconsistency about the exis-
tence of some binary compounds in the La–Sn and La–Ni
system [9–11]. In Refs. [2–4,15], the La–Ni phase diagrams
with eight compounds were reported. A phase-diagram
of the La–Sn system with seven compounds was reported
in Ref. [6] and a Ni–Sn binary phase diagram with three
compounds was reported in Ref. [7]. Structural data for the
intermetallic compounds in the three binary systems are
2
. Experimental
Each sample was prepared with a total weight of 3 g
by weighing appropriate amounts of the pure components
La: 99.9%, Ni: 99.99%, Sn: 99.99%). Three-hundred and
(
fifty-seven alloy buttons have been produced. These buttons
were prepared by arc melting on a water-cooled copper cast
with a non-consumable tungsten electrode under pure ar-
gon atmosphere. Each as-arc-cast button had been melted
three times and turned around after melting for better ho-
mogeneity. For most alloys, the weight loss is less than 1%
after melting. Therefore, no chemical analyses were carried
out.
∗
Corresponding author.
E-mail address: zhuang@gxu.edu.cn (Y. Zhuang).
0
925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0925-8388(03)00475-4

2
24
Y. Zhuang et al. / Journal of Alloys and Compounds 363 (2004) 223–226
Table 1
La–Ni–Sn binary crystal structure data
Compound
Space group
Lattice parameters (nm)
Reference
a
b
c
La7Ni3
LaNi
La2Ni3
La7Ni16
LaNi3
P63mc
Cmcm
Cmca
1.0130(9)
0.3907
0.51183
0.7355
0.5086(5)
0.5085
0.5016
0.3738(1)
0.4146
1.2214(6)
1.2748
0.8448
0.4782(3)
1.035
–
0.6462(6)
0.4396
0.79075
1.451(1)
2.501(1)
2.471
[8]
[8]
[8]
[8]
[8]
[8]
[8]
[17]
[17]
[17]
[15]
[15]
[15]
[15]
[15]
1.0810(1)
0.97316
–
–
–
–
–
–
0.4060(2)
–
1.626
1.194(1)
0.829
–
¯
I42m
¯
R3m
La2Ni7
LaNi5
P63/mmc
P6/mmm
0.3983
–
¯
Ni3Sn
Ni3Sn2
Ni3Sn4
La5Sn3
La5Sn4
LaSn
Pm3m
P63/mmc
C2/m
0.5253
0.5219(3)
0.6344
0.8604
0.4422(3)
1.063
I4/mcm
Pnma
Cmcm
La3Sn5
LaSn3
Cmcm
¯
Pm3m
0.47694(2)
–
Table 2
La–Ni–Sn ternary crystal structure data
Phase
Space group
Lattice parameters (nm)
Reference
a
b
c
LaNi5Sn
P63/mmc
0.4971(5)
0.7766(3)
0.4459
0.4526(1)
0.4584(2)
1.1965(1)
0.7671
–
–
–
1.999(3)
0.7581(3)
1.030
0.4510(1)
0.4587(2)
–
[16]
[16]
[16]
[16]
[16]
[16]
[16]
[16]
¯
LaNi4Sn2
LaNi2Sn2
La3Ni2Sn6
La3Ni2Sn7
La3Ni8Sn16
LaNiSn
I4c2
I4/mmm
Cmcm
1.7790(4)
2.751(1)
–
0.4652
–
Cmmm
¯
Im3
Pnma
0.7592
0.40389
La5Ni24Sn
P6/mmm
0.50723
After casting, the samples were sealed in an evacuated
quartz tube or glass tube for homogenization treatment and
then they were annealed at different temperatures in order to
attain good homogenization. The heat treatment temperature
of the alloys was determined by differential thermal analysis
a current of 250 mA. Some typical alloys were analyzed
by an S-570 scanning electron microscope (SEM), electron
probe microanalysis (EPMA) or differential thermal analy-
sis (DTA). By all these means, the phases and the crystal
structures of the alloys in the La–Ni–Sn ternary system
were determined.
(DTA) results of some typical ternary alloys or based on
previous work of the three binary phase diagrams and the
La–Ni–Sn ternary system [2,6–8]. The buttons in the Sn-rich
part, containing more than 75% Sn in the La–Sn binary
system or 57.1% Sn in the Ni–Sn binary system or near
them in the ternary system, were kept at 483 K for 960 h.
The alloys in the La-rich part, which contained more than
3. Results and discussion
3.1. Binary system
5
0% La were annealed at 773 K for 720 h at first and then
3.1.1. La–Ni system
cooled down to 673 K at a rate of 0.15 K/min, then kept
at 673 K for 240 h. The alloys in the La–Sn binary system
were homogenized at 903 K for 720 h at first and then they
were cooled down to 673 K at a rate of 0.15 K/min, and
finally kept at 673 K for 240 h. Finally, all these annealed
buttons were quenched in liquid nitrogen.
Eight kinds of La–Ni compound, La Ni, La Ni , LaNi,
3
7
3
La Ni , La Ni , LaNi , La Ni , LaNi , have been reported
2
3
7
3
2
7
16
5
in the La–Ni binary system [2] (Table 1). But according to
Ref. [3], LaNi exists instead of La Ni . Our investigation
2
7
16
has shown that the phase is La Ni , not LaNi , which was
7
2
16
found by XRD, SEM and EPMA. Secondly, the existence
Most homogenized alloy powders or buttons were in-
vestigated by X-ray diffraction, which was carried out on
a Rigaku D/Max 2500PC X-ray diffractometer (Cu K␣
monochromator) using JADE5 software [5] with analyzed
of La Ni was confirmed in Ref. [2,3]. Under our present
3
experimental conditions, we did not find the La Ni phase.
3
The alloys containing 75% La and 25% Ni or close to this
ratio contain the La phase and the La Ni phase in terms of
7
3
◦
angle ranging from 2θ = 20–60 at a voltage of 50 kV, and
the results of XRD.

Y. Zhuang et al. / Journal of Alloys and Compounds 363 (2004) 223–226
225
3
.1.2. Ni–Sn system
In the Ni–Sn system, three compounds were reported in
the literature [7] (Table 1). They are Ni3Sn, Ni3Sn2, and
Ni3Sn4, which is in agreement with our experiment results.
3
.1.3. La–Sn system
According to Ref. [6], there are seven kinds of compounds
in the La–Sn binary system, which are La Sn3, La Sn4,
5
5
La11Sn10, LaSn, La2Sn3, La3Sn , and LaSn3 (Table 1). But
5
in Ref. [6], we also find that the La11Sn10 and La2Sn3 com-
pounds might exist. That is to say, their existence has not
been confirmed. In our investigation, the phases of La11Sn10
and La2Sn3 were not observed either. Their X-ray diagrams
consist of La Sn4 and LaSn, La3Sn and LaSn.
5
5
3
.2. Ternary phases
Eight ternary compounds, LaNi Sn, LaNi4Sn2, LaNi2Sn2,
5
La3Ni2Sn , La3Ni2Sn7, La3Ni8Sn , LaNiSn and La Ni24Sn,
6
16
5
were reported in the literature [8]. All these compounds
Fig. 1. The isothermal section of the La–Ni–Sn ternary system at 673
and 483 K. (A) LaNi5Sn; (B) LaNi4Sn2; (C) LaNi2Sn2; (D) La3Ni2Sn6;
except La Ni24Sn (LaNi4.8Sn0.2) (Table 2) were confirmed
5
(E) La3Ni2Sn7; (F) LaNiSn3; (G) La3Ni8Sn16; (H) LaNiSn.
in our ternary alloys. After strict analysis by XRD and
DTA, we have determined that La Ni24Sn is just a solid
5
solution which was obtained through Sn substituting for
samples, evidence was found to confirm the existence of
a new ternary compound, whose atomic ratio is close to
La/Ni/Sn = 1:1:3. Its crystal structural data will be published
in another article.
part of Ni in LaNi alloys. LaNi and La Ni24Sn have the
5
5
5
same structure type, approximately the same crystal data
and diffraction patterns.
A new ternary compound in the La–Ni–Sn ternary sys-
tem, LaNiSn3, was observed in our experiment. Therefore,
there are in total eight kinds of ternary compounds in our
isothermal section.
3
.4. Isothermal section
The isothermal sections of the ternary La–Ni–Sn system
at 673 and 483 K were determined by XRD, EPMA, SEM
and DTA. The isothermal sections, shown in Fig. 1, consist
of 26 single-phase regions, 56 two-phase regions and 32
three-phase regions. Details of the three-phase regions are
3
.3. The existence of LaNiSn3
By comparing and analyzing the X-ray diffraction patterns
of the samples which contained almost 20% La, 20% Ni,
0% Sn, and by identifying the phases in each of these
given in Table 3. The maximum solubility of Sn in LaNi is
about 8 at.%.
5
6
Table 3
Details of three-phase regions in La–Ni–Sn system
Phase region
Phase composition
Phase region
Phase composition
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
Ni + LaNi5 + LaNi5Sn
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
La3Ni2Sn7 + LaSn3+La3Ni2Sn6
LaNiSn + La3Sn5+La3Ni2Sn6
LaNiSn + La3Sn5+LaSn
LaNiSn + La5Sn4+LaSn
LaNiSn + La5Sn3+LaSn
La + La5Sn3+La7Ni3
Ni + Ni3Sn + LaNi5Sn
LaNi4Sn2 + Ni3Sn + LaNi5Sn
LaNi4Sn2 + Ni3Sn + Ni3Sn2
LaNi4Sn2 + LaNi2Sn2 + Ni3Sn2
LaNi2Sn2 + Ni3Sn4 + Ni3Sn2
LaNi2Sn2 + Ni3Sn4 + La3Ni2Sn6
La3Ni2Sn7 + Ni3Sn4 + La3Ni2Sn6
LaNiSn3 + Ni3Sn4 + La3Ni2Sn7
LaNiSn7 + Ni3Sn4 + La3Ni8Sn16
LaSn3 + Ni3Sn4 + La3Ni8Sn16
LaSn3 + Ni3Sn4 + Sn
LaNiSn + La5Sn3+LaNi
La7Ni3+La5Sn3 + LaNi
LaNiSn + La2Ni3+LaNi
LaNiSn + La2Ni3+La7Ni16
LaNiSn + LaNi3+La7Ni16
LaNiSn + La2Ni7+La7Ni16
LaNiSn + LaNi5+La2Ni7
LaNi2Sn2+LaNiSn + LaNi5
LaNi2Sn2+LaNi4Sn2 + LaNi5
LaNi5Sn+LaNi4Sn2 + LaNi5
1
1
1
1
1
1
1
LaSn3 + LaNiSn3 + La3Ni8Sn16
LaSn3 + LaNiSn3 + La3Ni2Sn7
LaSn3 + La3Sn5 + La3Ni2Sn6
LaNi2Sn2 + LaNiSn + La3Ni2Sn6

2
26
Y. Zhuang et al. / Journal of Alloys and Compounds 363 (2004) 223–226
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. Conclusion
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The purpose of the present study was to determine the
phase relationships in the system La–Ni–Sn at 673 and 483
K and determine the crystal structure of the observed ternary
phases. A new ternary compound, LaNiSn3, was found. The
atomic ratio of this new phase is close to La/Ni/Sn = 1:1:3
and its crystal structural data will be published in another ar-
ticle. The two isothermal sections consist of 26 single-phase
regions, 56 two-phase regions and 32 three-phase regions.
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