Phase relations in the Zn3As2-ZnAs 2-CdAs2-Cd3As2 system

Article abstract of DOI:10.1023/A:1025592802171

Phase relations along the Cd₃As₂-ZnAs₂ and Zn₃As₂-CdAs₂ joins are studied by differential thermal analysis, x-ray diffraction, and microstructural analysis. The results, in conjunction with

Full text of DOI:10.1023/A:1025592802171

Inorganic Materials, Vol. 39, No. 9, 2003, pp. 911–915. Translated from Neorganicheskie Materialy, Vol. 39, No. 9, 2003, pp. 1064–1068.
Original Russian Text Copyright © 2003 by Marenkin, Vol’fkovich, Mikhailov, Astakhov.
Phase Relations
in the Zn As –ZnAs –CdAs –Cd As System
3
2
2
2
3
2
S. F. Marenkin, A. Yu. Vol’fkovich, S. G. Mikhailov, and V. V. Astakhov
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
e-mail: marenkin@rambler.ru
Received December 23, 2002; in final form, March 25, 2003
Abstract—Phase relations along the Cd As –ZnAs and Zn As –CdAs joins are studied by differential ther-
3
2
2
3
2
2
mal analysis, x-ray diffraction, and microstructural analysis. The results, in conjunction with earlier data on the
CdAs –ZnAs , Zn As –Cd As , Cd As –CdAs , and ZnAs –Zn As binaries, are used to map out the phase
2
2
3
2
3
2
3
2
2
2
3
2
diagram of the liquidus surface in the composition region Zn As –ZnAs –CdAs –Cd As of the ternary system
3
2
2
2
3
2
Cd–As–Zn. The ternary eutectic revealed in this region has an approximate composition of 26 at. % Cd +
6
5 at. % As + 9 at. % Zn and melts at 863 K.
INTRODUCTION
Yakimovich et al. [15], cadmium tetraarsenide is a
metastable phase.
The study of the Zn As –ZnAs –CdAs –Cd As
2
3
2
2
2
3
Analysis of earlier results [6, 15–19] indicates that
the Cd As –ZnAs and CdAs –Zn As joins lie within
system is of interest for the preparation of solid solu-
3
2
2
2
3
2
tions based on II–V semiconductors. The constituent
the quadrangle formed by the Cd As –CdAs , CdAs –
3
2
2
2
arsenides, crystallizing in monoclinic (ZnAs ) or tet-
2
ZnAs , ZnAs –Zn As , and Zn As –Cd As joins. The
2
2
3
2
3
2
3
2
ragonal (CdAs , Zn As , Cd As ) symmetry [1–6],
2
3
2
3
2
first three systems are of a eutectic type, while Zn As
3
2
offer a number of attractive physicochemical, optical,
and Cd As form a continuous series of solid solutions.
3
2
and electrical properties. Owing to the pronounced
anisotropy in the thermoelectric power of ZnAs and
The interest in the Zn As –ZnAs –CdAs –Cd As
3 2 2 2 3 2
2
CdAs single crystals, they are potentially attractive as system is also motivated by the search for compositions
2
suitable for growing eutectic layers of solid solutions
by liquid-phase epitaxy. As in the case of III–V com-
pounds [20], the use of a nonvolatile metal with a rela-
tively low melting point (Zn or Cd) as a solvent in II–V
epitaxy is of great benefit.
materials for nonselective radiation detectors [7]. Both
ZnAs and CdAs can be used in the fabrication of III–
2
2
V-based semiconductor devices [8]. Cadmium diars-
enide offers high optical activity, which makes it a can-
didate material for optical modulators and various
polarizing devices [9, 10]. Zinc diarsenide can be used
as a material for solid-state lasers [11]. In view of this,
considerable research effort has recently been concen-
trated on the preparation and physicochemical studies
EXPERIMENTAL
Zn As –ZnAs –CdAs –Cd As samples were pre-
3
2
2
2
3
2
of perfect single crystals of zinc and cadmium ars- pared from fine-particle ZnAs , Zn As , CdAs , and
2
3
2
2
enides and related materials.
Cd As powders presynthesized from cadmium and
3 2
zinc of 99.999+% purity and V5 arsenic via vacuum
melting as described in [4, 5, 7, 8]. The process was run
in double-wall silica tubes, which were graphitized to
prevent reaction between the melt and silica. After
loading the starting mixtures, the tubes were pumped
down to 10 Pa and sealed off. The tubes were
mounted in a steel block, which was then introduced
into a SShchOL vertical furnace. The temperature dif-
ference along the length of the tube was ±1 K.
Perfect ZnAs and CdAs crystals could be prepared
2
2
by vertical Bridgman growth [12, 13]. The structural
perfection of the crystals was shown to depend prima-
rily on the solidification rate, the temperatures of the
melting and solidification zones, and the amount of
excess arsenic. Single crystals grown under optimal con-
ditions were 20–30 mm in diameter and 100–150 mm in
length.
–
3
The systems Zn–As and Cd–As, which are the con-
stituent binaries of the ternary system Cd–Zn–As, are
To prepare the constituent arsenides, the tempera-
ture was raised at a rate of 20 K/h to the melting point
of the corresponding metal (Zn or Cd) and then main-
tained constant for 10 h. As a result, molten metal
known to contain the following compounds: Zn As ,
3
2
ZnAs , Cd As , CdAs , and CdAs [1, 14]. Zn As and
2
3
2
2
4
3
2
ZnAs are isovalent with their Cd analogs. According to spread over arsenic. Next, the metal and arsenic were
2
0
020-1685/03/3909-0911$25.00 © 2003 MAIK “Nauka/Interperiodica”

9
12
MARENKIN et al.
reacted by raising the temperature at 3–5 K/h to the homogenization at 823 K (40 K below the melting point
melting point of the arsenide. After isothermal melt of the ternary eutectic) until both the splitting of dou-
homogenization for 48 h, the temperature was lowered blet peaks in the x-ray powder diffraction pattern of the
at 10–12 K/h to about 2/3 of the melting temperature of sample and its microhardness remained unchanged.
the arsenide, which led to directional solidification by
the Tammann process and additional purification of the
sample. Next, the sample was annealed at this temper-
ature to relieve thermal stresses.
T, K
(a)
The other samples were prepared in a similar man-
ner, using the melting temperatures of the constituent
arsenides as “reference” points. The highest process
temperature was 10–15 K above the melting point of
the sample. The reaction was run for 200 h, followed by
1
200
T, K
1
100
(
a)
1
1
100
000
I
III
I
III
1
000
II
V
V
IV
II
9
00
9
00
VI
IV
CdAs2 20
VI
Cd As 20
40
60
80 ZnAs2
3
2
40
60
80 Zn As
3 2
mol %
mol %
(
b)
(b)
Fig. 1. (a) Phase diagram of the Cd As –ZnAs join: (I) liq-
Fig. 2. (a) Phase diagram of the CdAs –Zn As join: (I) liq-
2 3 2
3
2
2
uid, (II) liquid + Cd3 – xZn As , (III) liquid + ZnAs ,
uid, (II) liquid + CdAs , (III) liquid + Cd
Zn As ,
x
2
2
2
3 – x x 2
(
IV) liquid + CdAs + Cd
Zn As , (V) liquid + ZnAs +
(IV) liquid + CdAs + Cd
Zn As , (V) liquid + ZnAs +
2
3 – x
x
2
2
2
3 − x x 2 2
Cd3 – xZn As , (VI) CdAs + ZnAs2 + Cd3 – xZn As .
Cd3 – xZn As , (VI) CdAs + ZnAs2 + Cd3 – xZn As .
x
2
2
x
2
x 2 2 x 2
(
b) Microstructure of the sample containing 90 mol %
(b) Microstructure of the sample containing 90 mol %
Zn As ; ×200.
ZnAs ; ×200.
2
3
2
INORGANIC MATERIALS Vol. 39 No. 9 2003

PHASE RELATIONS IN THE Zn As –ZnAs –CdAs –Cd As SYSTEM
913
3
2
2
2
3
2
CdAs2
e2 (879 K)
ZnAs2
8
Es
63
1023
9
50
e3
e1
883 K)
950
(1023 K)
(
1
000
1
050
1
100
1
150
200
250
1
1
Fig. 4. Microstructure of the alloy with the composition
26 at. % Cd + 65 at. % As + 9 at. % Zn; ×200.
Cd As
Zn As
3 2
3
2
Fig. 3. Phase diagram of the liquidus surface in the compo-
sition region Zn As –ZnAs –CdAs –Cd As of the
1.65 MPa, respectively [21–23]). Microstructures were
examined in reflected light under an MIM-7 metallurgi-
cal microscope (×400) and MIN-9 polarizing micro-
scope (×230). Microhardness was measured on a PMT-3
tester.
3
2
2
2
3
2
Cd−As–Zn system; E is the ternary eutectic at 26 at. % Cd,
s
6
5 at. % As, and 9 at. % Zn, with a melting point of 863 K.
The samples were characterized by differential ther-
mal analysis, x-ray diffraction, and microstructural
analysis. The composition of individual phases was
determined by comparing the measured microhardness
RESULTS AND DISCUSSION
Our results indicate that neither the Cd As –ZnAs
2
3
2
H with the known microhardness values of ZnAs2, nor the Zn As –CdAs join is pseudobinary. The liqui-
3
2
2
Zn As , CdAs , and Cd As (3.25, 3.00, 2.90, and dus along the Cd As –ZnAs join consists of two pri-
3
2
2
3
2
3
2
2
1
00
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
2
0
30
40
50
2θ, deg
Fig. 5. X-ray scan of the alloy with the composition 26 at. % Cd + 65 at. % As + 9 at. % Zn.
INORGANIC MATERIALS Vol. 39 No. 9 2003

9
14
MARENKIN et al.
mary crystallization branches (Fig. 1a). In the compo-
3. Lazarev, V.B., Shevchenko, V.Ya., and Marenkin, S.F.,
Physicochemical Properties and Applications of II–V
Semiconductors, Izv. Akad. Nauk SSSR, Neorg. Mater.,
sition range 0–85 mol % ZnAs , the primary phase is
2
Cd3 – xZn As . Between 85 and 100 mol % ZnAs , the
x
2
2
1
979, vol. 15, no. 10, pp. 1701–1712.
primary phase is the ZnAs -based solid solution. The
2
join contains a ternary eutectic, which melts at 863 K.
Microstructural analysis confirms these phase relations
throughout the composition region studied. Figure 1b
shows the microstructure of the alloy containing
4. Turner, W.J., Fischer, A.S., and Reese, W.E., Physical
Properties of Several II–V Semiconductors, Phys. Rev.,
1
961, vol. 121, no. 3, pp. 759–767.
5
6
7
. Ugai,Ya.A. and Zyubina, T.A., Crystal Growth and Elec-
tronic Properties of Zinc Arsenides, Izv. Akad. Nauk
SSSR, Neorg. Mater., 1966, vol. 2, no. 1, pp. 9–16.
9
0 mol % ZnAs . One can see light crystallites of the
2
primary phase ZnAs and precipitates of cocrystallizing
2
Cd3 – xZn As and ZnAs . The ternary eutectic is almost
x
2
2
. Marenkin, S.F. and Trukhan, V.M., Phase Relations of
the Zn–Cd–P–As System, Russ. J. Inorg. Chem., 2001,
vol. 46, suppl. 3, pp. 187–202.
indiscernible because its amount is very small.
In the CdAs –Zn As join (Fig. 2a), the liquidus also
2
3
2
consists of two primary crystallization branches. The
. Lazarev, V.B., Marenkin, S.F., Raukhman, A.M., et al.,
Materials Based on Compounds of Zn and Cd with P, As,
and Sb, in Fundamental’nye nauki narodnomu
khozyaistvu (Basic Research for the National Economy),
Moscow: Nauka, 1990, pp. 225–226.
primary phases are the CdAs -based solid solution in
2
the composition range 0–10 mol % Zn As and the
3
2
Cd3 – xZn As solid solution between 10 and 100 mol %
x
2
Zn As . Between Ӎ20 and 80 mol % Zn As ,
3
2
3
2
Cd3 − xZn As and ZnAs cocrystallize. The thermal
x
2
2
8. Marenkin, S.F., Lazarev, V.B., Pashkova, O.N., et al.,
Compounds of Zinc and Cadmium with Phosphorus and
Arsenic as Sources of Acceptor Impurities in III–V
Semiconductors, Izv. Akad. Nauk SSSR, Neorg. Mater.,
effect at 863 K is due to the crystallization of the ter-
nary eutectic. The microstructures of CdAs –Zn As
2
3
2
samples correlate with the phase diagram of this join.
The micrograph of the alloy containing 90 mol %
1
990, vol. 26, no. 11, pp. 1814–1818.
Zn As (Fig. 2b) shows elongated crystallites of the pri-
3
2
9. Lazarev, V.B., Malinko, V.N., Marenkin, S.F., et al.,
mary phase Cd3 – xZn As , embedded in the ternary
Gyrotropy of CdAs Semiconductor Crystals, Izv. Akad.
x
2
2
eutectic.
Nauk SSSR, Neorg. Mater., 1985, vol. 21, no. 7,
pp. 1082–1085.
The dashed lines in Figs. 1a and 2a represent the
thermal effects due to the polymorphic transformations 10. Marenkin, S.F., Raukhman, A.M., Matiuk, I.N., and Laz-
of Zn As and Cd As . Analogous transformations in
arev, V.B., Birefringence and Optical Activity of Cad-
mium Diarsenide Single Crystals, Opt. Eng., 1994,
vol. 33, no. 9, pp. 3034–3037.
3
2
3
2
the ternary system were not studied.
The present and earlier [6, 15–19] results were used
to construct the phase diagram of the liquidus surface in 11. Lazarev, V.B., Marenkin, S.F., Chukichev, M.V., and
Raukhman, A.M., Stimulated Emission of ZnAs Single
the composition region Zn As –ZnAs –CdAs –Cd As
2
3
2
2
2
3
2
Crystals, CLEO/Europe-EQEC, 1994, p. 68.
(Fig. 3). The ternary eutectic revealed in this region has
an approximate composition of 26 at. % Cd + 65 at. %
As + 9 at. % Zn and melts at 863 K. The microstructure
and x-ray diffraction pattern of a sample with the eutec-
tic composition are shown in Figs. 4 and 5, respectively.
1
2. Marenkin, S.F., Maimasov, A.B., and Popov, V.A.,
Growth of ZnAs Single Crystals by Directional Solidi-
2
fication in a Bridgman Geometry, Neorg. Mater., 1997,
vol. 33, no. 4, pp. 398–403 [Inorg. Mater. (Engl. Transl.),
vol. 33, no. 4, pp. 330–334].
CONCLUSIONS
13. Marenkin, S.F., Raukhman, A.M., Maimasov, A.B., and
Popov, V.A., Growth of CdAs Single Crystals by Direc-
2
Phase relations in the Zn As –ZnAs –CdAs –
3
2
2
2
tional Solidification in Bridgman Geometry, Neorg.
Mater., 1997, vol. 33, no. 12, pp. 1439–1447 [Inorg.
Mater. (Engl. Transl.), vol. 33, no. 12, pp. 1220–1226].
Cd As system were studied by physicochemical anal-
ysis. The system was shown to contain a ternary eutec-
tic with an approximate composition of 26 at. % Cd +
5 at. % As + 9 at. % Zn, which melts at 863 K.
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