On Some Ternary Phases in the Systems Nb-Zn-Al and Ta-Zn-Al
A. Drašner and Ž. Blažina*
Institute "Ruder Boskovic", 41001 Zagreb, POB 1016, Yugoslavia
Z. Naturforsch. 37b, 1225-1229 (1982); received May 17, 1982
Aluminium, Niobium, Tantalum, Zinc, Alloy
In the systems NbZi^-aALr and TaZn2_^Alz a great number of samples was prepared
and investigated by means of X-ray powder diffraction. In both systems at the equiatomic composition two new ternary phases were found. Their crystal structures were
determined and found to belong to the Friauf-Laves type (MgZm prototype, S. G.
P 63/mmc). The unit cell parameters of NbZnAl are a = 5Ö6.4 ± 0.2 pm, c = 829.9 ± 0.8
pm, c/a = 1.639, and for TaZnAl a = 503.8 ± 0.2 pm, c = 827.9 ± 0.3 pm, c/a= 1.643. In
the system NbZno-a-Al^, at the composition NbZn1.25Alo.75, a ternary phase of the A11C113
structure (a= 394.4 i 0.3 pm, S. G. Pm3m) was also observed, while in the system
NbZns-zAl^ a single phase region, having the A11C113 structure, was found to exist up to
the composition NbZmAl. The stability of these Friauf-Laves phases and those found
previously in the systems ZrZn2_J-Alj; and HfZm-zAlz is discussed in terms of atomic
sizes and valence electron concentration.
Introduction
In our paper [1] the results of substitution studies
of zinc by aluminium in some A B 2 phases were
described. It is well known that aluminium is a
common component in a great number of binary
Friauf-Laves phases, as well as a stabilizer of some
ternary F. L. phases, especially those at the stoichiometric ratio 1 : 1 : 1 . Because of that, we were
interested in further substitutional studies of zinc
with aluminium in some related systems.
In the corresponding binary systems of the
systems N b - Z n - A l and T a - Z n - A l it is interesting
to mention the existence of NbZn2, TaZn2, NbZn 3 ,
NbAl 3 and TaAl 3 . NbZn 2 is a Friauf-Laves phase
(MgNi 2 -type) [2], but there are some data about a
cubic variant of the MgCu2-type [3]. TaZn2 also
seems to be a F. L. phase (MgZn2 or MgNi2-tvpe)
but the available data are very scarce [3]. NbZn3 is
cubic (AUCU3 structure) and NbAl3 and TAAL3 have
the tetragonal structure of the TiAl 3 -type [4].
TaAl2, NbAl2 and TaZn3 do not exist, while zinc and
aluminium do not form intermetallic compounds
[ref. [4], p. 389.].
Experimental
Samples of the general formula N b Z ^ - z A l z ,
NbZn3_aAla; and TaZi^-xAl* were prepared by direct
synthesis from elements in evacuated silica tubes.
Depending on the results of the X-ray phase
analysis and/or in order to prepare single phase
alloys, samples were annealed at 800 °C for 1Ö80 h,
at 900 c C or 1000 °C for 72 h.
X-ray powder diffraction patterns were taken on
a Philips diffractometer P W 1050 using nickel filtered CuKa radiation. Silicon was used as an internal
standard.
X-ray diffraction intensities were calculated on a
Univac 1100 computer using " L A Z Y - P U L V E R I X "
computer program [5].
Results
System
Nb-Zn-Al
NbZno-NbAh
tie line
The results of X - r a y phase analysis of samples
annealed at 800 °C for 1080 h indicated the existence of two ternary phases near the compositions
NbZnAl and NbZn1.25Alo.75, respectively, but the
alloys were not single phase. Single phase alloys
were obtained when the temperature was elevated
up to 1000 °C for 72 h.
Metallic powders used in this investigations were:
niobium (99.5%), tantalum (99.9%), aluminium
(99%) (all from Koch-Light Laboratories Ltd.) and
zinc (Kemika, Zagreb, Reagent grade).
The crystal structure of NbZnAl was determined
on the basis of obvious correspondence to hexagonal
Friauf-Laves phase of the MgZn 2 type (S. G.
P6 3 /mmc) with a = 506.4 ± 0 . 2 pm, c = 829.9 ±
0.8 pm and cja = 1.639.
* Reprint requests to Z. Blazina.
0340-5087/82/1000-1225/S 01.00/0
The best agreement between calculated and observed intensity values is obtained if the following
atomic positions are assumed:
Materials and Methods
Unauthenticated
Download Date | 6/18/17 6:39 PM
1226
4 Xb
A. Drasner-Z. Blazina • On Some Ternary Phases in the Systems Nb-Zn-Al and Ta-Zn-Al
in 4(f)
IZn + 1A1 in 2(a)
(statistically)
1/3, 2/3, 2, 2/3, 1/3, 2, 2/3, 1/3,
1/2 + 2, 1/3, 2/3, 1/2—2,
0,0,0,0,0,1/2,
3Zn + 3 Al in 6(h) x, 2x, 1/4, x, x, 1/4, 2x, x, 1/4,
(statistically)
2x, x, 3/4, x, 2x, 3/4, x, x, 3/4
The variable parameters were found to be
2 = 0.0635 and x = 0.8333. Table I shows the relevant diffraction data.
Tab. I. X-ray diffraction data for NbZnAl (CuKa).
hkl
Do(pm)
D c (pm)
100
002
101
102
110
103
200
112
201
004
202
104
203
210
211
105
212
204
300
213
006
302
205 \
106 /
214,303
220
438.3
414.4
387.6
301.4
253.3
233.9
219.3
216.2
212.0
207.4
193.7
187.6
171.8
n.o.
162.4
155.3
153.9
n.o.
146.2
142.1
138.3
137.9
132.2
438.5
415.0
387.8
301.4
253.2
234.0
319.3
216.1
212.0
207.5
193.9
187.6
171.8
165.7
162.5
155.2
153.9
150.7
146.2
142.2
138.3
137.9
132.3
131.9
129.4
126.6
129.5
126.6
Io
6
2
4
8
54
93
18
100
70
11
4
5
1
n.o.
1
8
5
n.o.
10
42
4
27
30
3
26
NbZnz-NbAlz
tie line
At this tie line (800 c C and 1000 : C) the crystal
structure of binary NbZn 3 extends into the ternary
field, i.e. substitution of zinc with aluminium is
possible up to 25 at. % of Zn, corresponding thus
the formula NbZn 2 Al. The unit cell parameter
variation is shown on Fig. 1. and Table II. These
variations are also small but it can be stated that
Vegard's rule is obeyed. It is interesting to mention
that the sample of the composition NbZn 2 Al in
some cases (800 °C/45 d) shows a tendency to double
one of its cubic axes becoming thus tetragonal. The
crystal structure of this phase was determined as a
TiAl 3 type with a = 382.9 pm, c = 864.4 pm and
c/a = 2.258.
Ic
3
2
5
9
56
93
14
100
63
9
3
6
1
1
1
7
3
1
10
36
4
22
30
3
22
R = 7.89%
The crystal structure of the second alloy,
NbZn1.25Alo.75, was determined as a cubic one of
the AuCu 3 type (S. G. Pm3m) with a = 394.4 ±
0.3 pm. It ^as found that its homogeneity region
spans the compositions between NbZn1.25Alo.75 and
N b Z m 5A1 0.5. Lattice parameter variation was not
observed in this region, probably due to relatively
small differences in atomic radia (R A I = 142.9 pm
and R Z n = 137.9 pm).
396 -
392 -
390 -J
0
t
,
1
T
1
5
10
15
20
25
-
A I (at.%)
Fig. 1. The unit cell parameter variation in the single
phase region of the system NbZns-aAlz.
Tab. II. The unit cell parameters in the single phase
region of the system NbZn3_xAl^.
Composition
at, % Al
NbZn 3
NbZn2.67Alo.33
NbZn2.4Al0.6
NbZn 2 Al
0
8.25
15
25
o(pm) ( ± 0.2)
393.4
393.9
393.9
394.5
System
Ta-Zn-Al
TaZm-TaAh
tie line
The only single phase alloy obtained in this
system is formed at the composition TaZnAl after
the heat treatment at 1000 °C for 72 h. Its crystal
structure was found to belong to Friauf-Laves
phase of the MgZn 2 -type with a = 503.8 ± 0 . 2 pm.
c = 827.9 ± 0.3 pm and c/a = 1.643. Atoms occupy
the same positions within the unit cell as described
Unauthenticated
Download Date | 6/18/17 6:39 PM
1227 A. Drasner-Z. Blazina • On Some Ternary Phases in the Systems Nb-Zn-Al and Ta-Zn-Al
for NbZnAl. Variable coordinates were found to be
z = 0.0635 and x = 0.8333. The corresponding diffraction data are presented in Table III.
Tab. III. X-ray diffraction data for TaZnAl (CuKa).
hkl
do(pm)
d c (pm)
Io
lc
100
002
101
102
110
103
200
112
201
004
104
203
210
211
105
212
300
213
006
302
205 \
106 j
214
220
116,310
222
436.2
413.7
386.0
300.4
251.9
233.8
218.4
215.5
211.2
206.9
187.1
171.1
164.8
161.7
154.8
153.2
145.4
141.6
138.0
137.2
131.9
436.3
414.0
386.0
300.3
251.9
233.2
218.2
215.2
211.0
207.0
187.0
171.1
164.9
161.7
154.8
153.2
145.4
141.6
138.0
137.2
131.9
131.6
129.0
126.0
121.0
120.5
26
13
16
21
63
100
25
83
43
4
2
13
6
5
17
12
18
46
4
22
25
25
15
21
19
73
100
16
86
39
3
2
11
4
4
16
6
14
42
4
20
27
1
18
4
1
1
18
4
2
129.0
126.0
121.0
120.5
R = 10.54%
As mentioned before, there are some literature
data [3] which allow that TaZn 2 assumes a FriaufLaves structure, but in our investigations this
phase was not observed in the temperature region
between 400 °C and 1000 °C.
One further point. In both systems samples annealed at temperatures below 1000 °C contain solid
solution of aluminium and zinc. This could suggest
that zinc vapor (b. p. 906 °C) are necessary for these
reactions or the extremely long homogenization
times.
Discussion
The occurence of a ternary AuCu3 structure on
the NbZn 2 -NbAl 2 tie line in the composition region
N b Z m .25Alo.75-NbZn1.5Alo.5 deserves some further
remarks. W e believe that the presence of this
structure at the AB 2 stoichiometry can be attributed
to the widely extended homogeneity region of the
AuCu3 structure observed on the NbZn 3 -NbAl 3 line
in the region NbZn3-NbZn 2 Al.
The atomic arrangement within the unit cell was
calculated for the sample of the composition
NbZn1.25Alo.75. The best agreement with the observed intensity values is obtained if 1 N b atom is at
the position 1(a) and (0.333 N b - f 1.666 Z n + 1 Al)
statistically in 3(a). Thus the formula for all
samples with the AuCu3 structure can generally be
written as Nb(Nb,Zn, Al) 3 . This results are in good
agreement with the results observed in the systems
ZrZn2_3;AL and H f Z ^ - z A U where the occurence of
the AuCu3 structure was observed at the same composition [1],
It may be interesting to compare the ternary
Friauf-Laves phases described here with those
observed in some related systems, i.e. in ZrNi^xAlz,
ZrCua-zAl*, ZrZn 2 _*AL, HfNi 2 - a Al*, H f C u ^ A L ,
HfZn 2 _*Al*, NbNio.zAU NbCu 2 _*Al*, T a N i ^ A l *
and TaCu2_3;AL, in terms of valence electron concentration and relative atomic sizes. Tables I V - V
and Figs. 2-3. present crystallographic data of
these phases, their homogeneity regions, valence
Tab. IV. Homogeneity regions and VEC of ternary
Friauf-Laves phases in the systems ZrM2-2;Ala;,
HfMo^Al*, NbMa-sAl* and TaM2_*Alx (M = Ni, Cu or
Zn).
Composition
Type
VEC
Reference
ZrNio.eAl1.4ZrNio.2Ali.8
MgCu2
3.133
3.267
[6]
ZrCu0.95Al1.05ZrCuo.35Al1.65
ZrZno.eAl1.4ZrZn0.4Ali.e
MgCu2
2.700
3.100
[6]
MgCu2
3.133
3.200
[1]
HfNio.35Al1.es
MgCu2
3.217
[6]
HfCuo.35Al1.e5
MgCu2
3.100
[6]
HfZn1.25Alo.75HfZno.sAli.5
MgCu2
2.917
3.167
[1]
NbNi1.5Alo.5NbNi 0 . 3 Ali. 7
NbCuAl
MgZn2
3.163
3.565
[7]
MgZn2
3.000
NbZnAl
MgZn2
3.333
[7]
this paper
TaNiAl
MgZn2
3.333
[7, 8]
TaCuAlTaCuo-oAli.5
MgZn2
3.000
3.333
[9]
TaZnAl
MgZno
3.333
this paper
Valences used are:
Cu = 1, Ni,Zn = 2, Al = 3, Z r H f = 4 , Nb,Ta = 5.
Unauthenticated
Download Date | 6/18/17 6:39 PM
1228
A. Drasner-Z. Blazina • On Some Ternary Phases in the Systems Nb-Zn-Al and Ta-Zn-Al
Table V. The effective atomic radii (r), Pauling's radii for CN 12 (R) and radius ratios of ternary Friauf-Laves
phases listed in Table IV.
Composition
ZrNi0.4Ali.6
ZrCuo.35Al1.65
ZrZn 0 .4Ali. 6
HfNio.35Al1.65
HfCuo.35Al1.65
HfZno.sAli.s
NbNiAl
NbCuAl
NbZnAl
TaNiAl
TaCuAl
TaZnAl
Unit cell
parameter
(pm)
a = 740.4
a = 744.0
a = 748.3
a = 734.7
0 = 738.0
a = 741.4
a = 500.0
c = 809.3
A = 500.9
c = 805.8
a = 506.4
c = 829.9
a —496.9
c = 798.5
a = 496.0
c = 811.0
a = 503.8
c = 827.9
TA
(pm)
TB
(pm)
TA/I-B
RA
RB
RA/RB
160.3
161.1
162.0
159.1
159.8
160.5
147.9
130.9
131.5
132.3
129.9
130.5
131.1
124.5
1.225
1.225
1.224
1.225
1.225
1.224
1.188
159.7
159.7
159.7
158.5
158.5
158.5
145.6
139.2
140.2
141.9
139.7
140.2
141.7
133.7
1.147
1.139
1.125
1.135
1.131
1.119
1.089
152.6
124.4
1.227
145.6
135.3
1.076
151.9
126.8
1.198
145.6
140.4
1.037
151.4
123.4
1.227
145.7
133.7
1.090
151.9
124.1
1.224
145.7
135.3
1.077
151.2
126.3
1.197
145.7
140.4
1.038
(pm)
(pm)
A = Zr, Hf, Nb or Ta; B = (Ni, Al), (Cu, Al) or (Zn, Al) (statistically)
. ZrM,
electron concentrations (VEC), effective atomic
radii (r), Pauling's atomic radii for CN 12 (R), and
UO
the corresponding radius ratios. The effective radii "e 135
are calculated from the A - A and B - B distances CL
130
(for the MgZn 2 type phases average values were
125
taken, because the axial ration differ from the ideal
165
Jl60
155
HfM0AA>1.6
UO
SYSTEM
Zr-Ni-AI
Zr-Cu-Al
Zr-Zn-Al
Hf-Ni-Al
Hf-Cu-AI
Hf-Zn-AI
135
_ 165
-130
J.160-
MgCu2"TYPE
125
155-
NbMAI
UO
- 135
£
Nb-Ni-AI
Nb-CuAl
Nb-ZnAI
Ta-Ni-AI
Ta-Cu-Al
Ta-Zn-Al
155-
Q.
M g Z N 2 -TYPE
2.5
3,0
3.5
VEC
150-
-130
Q.
125
~ U5
120
UO
TqMAl
U0
Fig. 2. Valence electron concentrations of ternary Fri- - 135
auf-Laves phases in the systems ZrM^aAlz, HfMo-^Alj;, £
NbMa-sAl* and TaM2_xAlx (M = Ni, Cu or Zn).
— 130
Fig. 3. Effective (r) and Pauling's CN 12 (R) radii
variations of Friauf-Laves phases of the compositions
~ ZrM0 4Ali 6 , ~ HfM 0 jAli 6 , NbMAl and TaMAl
(M = Ni, Cu or Zn).
155
"e 150
Q.
125
U5
120
U0
t
I t
B = !Ni,Al) (CUjAI) (ZnAl)
1
(Ni, Al) (Cu,Al) (Z n, Al)
Unauthenticated
Download Date | 6/18/17 6:39 PM
1229 A. Drasner-Z. Blazina • On Some Ternary Phases in the Systems Nb-Zn-Al and Ta-Zn-Al
value c/a= 1.633). The atomic radii are calculated
for compositions common in all systems, i.e. AMA1
for MgZn 2 type phases and about AM0.4AI1.6 for
MgCu 2 type phases.
Some general remarks can be drawn: 1) In all
ternary systems presented in Table IV and Fig. 2.,
the MgZn 2 type phases generally form at higher
VEC, while the MgCu 2 structures are stabilized at
lower VEC. 2) The effective radius ratios (r A /rß) are
in all systems close to the ideal value j / 3 / j / 2 =1.225,
being for the MgCu 2 type phases practically identical and differing slightly for the MgZn 2 -type
(Table V). The radius ratios (R A /RB) for CN 12
differ greatly from the ideal value, i.e. they can
only be considered as a rough indication for the
rA/rB values.
An interesting feature is the small effective radii
of (Zn.Al) (statistically) with values close to the
values of (Ni, Al) (statistically) and (Cu,Al) (statistically) which are also contracted (Table V, Fig. 3.).
This is more pronounced in the systems containing
MgZn 2 type phases (probably as a result of the
smaller influence of aluminium). It seems that in
all systems an electron transfer from Ni, Cu or Zn
and/or Al to the IV or V group elements takes
place, becoming greater going from Ni to Zn and
from IV to V group element. In such a proposed
scheme Zn would release its d electrons and act as
a transition element. For more general conclusions
data on more Friauf-Laves phases should be gathered.
[1] A. Drasner and Z. Blazina, Z. Naturforsch. 36b,
1547 (1981).
[2] C. L. Void, Acta Crystallogr. 14, 1289 (1961).
[3] W. Rossteutscher and K. Schubert, Z. Metallkde.
06, 730 (1965).
[4] W. B. Pearson, A Handbook of Lattice Spacings
and Structure of Metals and Alloys, Pergamon
Press, New York, 1958, pp. 376, 385.
[5] K. Yvon, W. Jeitschko, and E. Parthe, J. Appl.
Crystallogr. 10, 73 (1977).
[6] V. Ja. Markiv and P. I. Kripjakevic, Kristallografija 11, 858 (1966).
[7] V. Ja. Markiv, Ju. V. Vorosilov, P. I. Kripjakevic, and E. E. Öerkasin, Ivristallografija 9, 737
(1964).
[8] J. B. Kusma and H. Nowotny, Monatsh. Chem.
95, 428 (1964).
[9] H. Nowotny and H. Oesterreicher, Monatsh.
Chem. 95, 982(1964).
Unauthenticated
Download Date | 6/18/17 6:39 PM