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FEDORCHENKO et al.
containing excess ZnAs2, X-ray diffraction patterns did not
(‡)
show noticeable shifts of diffraction peaks in the 2θ range
of 10° to 90° (Fig. 2b); this signifies the low component
solubilities and the existence of a narrow homogeneity
range for ZnSiAs2. Microstructure and XFA data sup-
port XRD data.
Figure 3 displays the micrographs of alloys with
overstoichiometric ZnSiAs2 proportion relative to
ZnAs2. All samples, except for the sample in Fig. 3a,
contain ZnSiAs2 (the light phase) and the eutectic
ZnSiAs2 + ZnAs2 (the dark phase). The eutectic preva-
lence increases with rising ZnAs2 concentration to
reach a maximum in the alloy containing 18 mol %
ZnSiAs2 + 82 mol % ZnAs2 or 9 mol % Si + 91 mol %
ZnAs2 (Fig. 3a).
Differential thermal analysis was carried out on an
NTR-70 Kurnakov’s pyrometer. A Pt–Pt/Rd thermo-
couple graduated against the reference points of chem-
ically pure compounds was the temperature gage. The
references used were zinc (692 K), antimony (903 K),
sodium chloride (1074 K), and germanium (1210 K).
The measurement accuracy was 4°ë K. The DTA
trace for the 9 mol % Si + 91 mol % ZnAs2 sample con-
tains a single peak at 630°ë.
(b)
X-ray fluorescence analysis was performed on an
EAGLE III µ-probe X-ray fluorescence analyzer at the
Microscopy and Analysis Systems Company. Linear
scanning was carried out along four lines 11–13 mm
long from both sizes of the sample. X-ray spectra from
100-µm spots were obtained using a tube with an Rh
anode at U = 40 kV and I = 250 µA at 50 points lying
at equal distances from one another along each line.
The accumulation time per spectrum was 10 s. Concen-
trations of chemical elements were determined by the fun-
damental parameters method without references using
software “No Standards” (EDAX). This program gives an
error of 5% for the major components (30–100%), 10%
for low concentrations (5–30%), and 50% for traces
(<3%).
(c)
Figure 4a is the micrograph of the cross section of
97 mol % ZnSiAs2 + 3 mol % Si ingot (x200).
Figures 4b–4d show the zinc, arsenic, and silicon distri-
butions in X-rays in the same region. These distribu-
tions are nonuniform.
Zinc and arsenic concentrations decrease and silicon
precipitates along block joins in polycrystals. The com-
position of the eutectic ZnSiAs2 + Si is ~ 80 ZnSiAs2 +
20 mol % Si, as shown by quantitative XFA (Fig. 5).
24
36 34 30 32 28 26
22 20 18 16 14 12
2θ, deg
The join Si–ZnAs2 was constructed on the basis of
our study (Fig. 6). The join Si–ZnAs2 is quasi-binary. The
congruently melting compound ZnSiAs2 (Tm = 1096°C)
and two eutectics (Si + ZnSiAs2 and ZnSiAs2 + ZnAs2)
are formed along this join.
To summarize, proceeding from the earlier analysis
of the binary subsystems Zn–As, Si–As, and Si–Zn [5],
here we have analyzed the Zn–Si–As ternary diagram.
Fig. 2. X-ray diffraction patterns for (a) ZnSiAs ,
2
(b) 50 mol % ZnSiAs + 50 mol % ZnAs and (c) ZnSiAs .
2
2,
2
data base. The precision of phase composition determi-
nation by XRD was 4%. Examination of diffraction
patterns (Fig. 2) showed that the samples contained Si,
ZnSiAs2, and ZnAs2 phases solely. For ZnSiAs2 samples
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 7 2008
Fedorchenko
