Interaction of the components in the systems Ce-Ag-Si at 500 °c and Eu-Ag-Si at 400 °c

Article abstract of DOI:10.1016/j.jallcom.2004.12.035

Isothermal sections of the phase diagrams of the systems Ce-Ag-Si and Eu-Ag-Si were built at 500 and 400 °C, respectively. Three intermetallic compounds were found in the former system, two in the latter and their crystal structures and homogeneity region

Full text of DOI:10.1016/j.jallcom.2004.12.035

Journal of Alloys and Compounds 396 (2005) 212–216
Interaction of the components in the systems Ce–Ag–Si at
500 ◦C and Eu–Ag–Si at 400 ◦C
B. Belana,∗, O. Bodaka, R. Gladyshevskiia, I. Sorokaa, B. Kuzhela, O. Protsykb, I. Stetsa
a
Ivan Franko National University of Lviv, Kyryla i Mefodiya St. 6, UA-79005 Lviv, Ukraine
b
Lviv Academy of Arts, Kubiyovych St. 38, UA-79000 Lviv, Ukraine
Received 11 December 2004; accepted 23 December 2004
Available online 26 January 2005
Abstract
Isothermal sections of the phase diagrams of the systems Ce–Ag–Si and Eu–Ag–Si were built at 500 and 400 ◦C, respectively. Three
intermetallic compounds were found in the former system, two in the latter and their crystal structures and homogeneity regions were
determined. The effective valence of europium in the CeAl2Ga2-type phase EuAg2Si2 was found to be 2+ over the whole homogeneity
range, based on LIII-absorption spectroscopy. The temperature dependence of the electrical resistivity, thermoelectric power and magnetic
susceptibility of this phase was also studied.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Silver-based systems; Phase diagram; Rare-earth compounds; Physical properties
1. Introduction
sults of the investigation of the Eu–Ag–Si system have been
reported in [6].
The results presented in this paper continue a system-
atic research on silver-based ternary systems with rare-earth
metals and main-group elements. The peculiar properties of
cerium and europium distinguish these elements from the
other rare-earth elements. The investigation of the interaction
of cerium and europium with other elements, the conditions
under which compounds are formed and the crystal structures
and properties of these, makes it possible to establish rela-
tions between the properties of the elements and their place
in the periodic system.
Several intermetallic compounds have been reported in R-
Ag–Si systems [1], however, isothermal sections have only
been built for the systems {La,Ce,Pr,Nd}–Ag–Si [2–5]. In
the Ce–Ag–Si system studied at 850 ◦C three compounds
have been identified: CeAg2Si2 (CeAl2Ga2-type structure),
2. Experimental
The investigation of the phase equilibria was based on 92
and 120 alloys for the systems Ce–Ag–Si and Eu–Ag–Si,
respectively. The samples were prepared by arc melting un-
der high-purity argon on a water-cooled copper hearth. The
starting materials were high-purity elements: cerium 99.89%,
europium 98.8%, silver 99.9%, and silicon 99.9999%. The
alloys were annealed for 2 weeks in evacuated quartz am-
poules, at 500 ◦C for the system Ce–Ag–Si and at 400 ◦C for
the system Eu–Ag–Si, and subsequently quenched in water.
The phase analysis was performed by X-ray powder
diffraction (Debye-Scherrer method, RKD-57.3, Cr K␣ radi-
ation). The lattice parameters were determined using a pow-
der diffractometer (DRON-2.0, Fe K␣ radiation or DRON-
3.0, Cu K␣ radiation). The crystal structures of the com-
pounds were studied by X-ray powder diffraction (automatic
diffractometer HZG-4a, Cu K␣ radiation).
Ce(AgxSi1−x 2−y
)
(x = 0.35–0.4, y = 0; AlB2-type structure)
and CeAgSi2 (unknown structure) [3]. Our preliminary re-
∗
Corresponding author.
E-mail address: belan@mail.lviv.ua (B. Belan).
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2004.12.035

B. Belan et al. / Journal of Alloys and Compounds 396 (2005) 212–216
213
The microstructures of some alloys were studied visually
using MIM8 and Neophot-30 microscopes.
The effective valence of europium was determined by
LIII-absorption spectroscopy at room temperature. Electric
resistance and thermoelectric power were measured with an
accuracy of not worse than 5 and 10%, respectively. Magnetic
susceptibility was measured by the Faraday method with 3%
accuracy.
3. Results and discussion
The systems {Ce,Eu}–Ag–Si (Fig. 1, Table 1) are char-
acterized by the formation of a few ternary compounds and
solid solutions based on several binary compounds. Accord-
ing to the phase diagram of the Ce–Ag–Si system at 500 ◦C,
the binary compounds of the systems Ce–Si and Ce–Ag dis-
solve no more than 5 at.% of the third component, except
CeSi2 with ␣-ThSi2-type structure (space group I41/amd),
which dissolves up to 18 at.% of silver (Fig. 2). The phase
analysis shows that on increasing the amount of silver in this
phase, the width of the homogeneity region gradually de-
creases from 3 to 1 at.% of cerium, without any significant
decrease of the unit-cell volume. The increase of the cell vol-
ume observed on increasing the silver content along the iso-
concentrate 33 at.% of cerium is explained by the formation
of a solid solution where Si atoms (rSi = 0.134 nm) are pro-
gressively replaced by larger Ag atoms (rAg = 0.144 nm). On
the contrary, along the isoconcentrate with a constant silver
content the lattice parameters remain practically unchanged,
which corresponds to the formation of a solid solution where
Si atoms are simply removed, and not replaced by the larger
Ce atoms (rCe = 0.183 nm).
A previously unknown compound, CeAg1.12Si0.88, which
crystallizes with a LaPtSi-type structure (space group I41md,
a = 0.42346(2), c = 1.4712(1) nm), was found in the sys-
tem Ce–Ag–Si. In addition, the existence of the com-
pounds CeAg2Si2 [7] (CeAl2Ga2 structure type, space group
I4/mmm) and CeAgSi [8] (AlB2 structure type, space group
P6/mmm) was confirmed. For the latter a significant homo-
Fig. 1. Isothermal sections of the (a) Ce–Ag–Si system at 500 ◦C and of the
(b) Eu–Ag–Si system at 400 ◦C.
with the lattice parameters changing from a = 0.4772(3),
b = 0.7498(7), c = 0.8187(7) to a = 0.4706(8), b = 0.7536(9),
c = 0.8167(8) nm within the homogeneity range (Fig. 3). It
should be noted, that the binary compound Eu2Si (PbCl2
structure type, space group Pnma), which was found in an
geneity region was found, CeAg0.90–1.10Si1.10–0.90
.
The binary compound EuAg2 (KHg2 structure type,
space group Imma) dissolves up to 15 at.% of Si,
Table 1
Crystallographic data of the ternary compounds in the systems {Ce,Eu}–Ag–Si
No.
Compound
Structure type
Space group
Lattice parameters (nm)
a
c
System Ce–Ag–Si
1
2
3
CeAg2Si2
CeAg1.12Si0.88
CeAg0.90–1.10Si1.10–0.90
CeAl2Ga2
LaPtSi
AlB2
I4/mmm
I41md
P6/mmm
0.4254(1)
0.42346(2)
0.4241(1)
1.0641(2)
1.4712(1)
0.4203(1)
for composition CeAgSi
System Eu–Ag–Si
1
2
EuAg2.00–1.25Si2.00–2.75
EuAg0.92–0.50Si1.08–1.50
CeAl2Ga2
AlB2
I4/mmm
P6/mmm
0.4315(1)–0.4321(1)
0.4202(1)–0.4150(1)
1.0463(2)–1.0454(6)
0.4463(2)–0.4477(3)

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B. Belan et al. / Journal of Alloys and Compounds 396 (2005) 212–216
Fig. 2. Lattice parameters of the solid solution of Ag in CeSi2.
Fig. 5. Lattice parameters in the homogeneity region of the compound
EuAg0.92–0.50Si1.08–1.50
.
Fig. 6. LIII-absorption spectra of the samples: (1) EuAg1.25Si2.75; (2)
EuAg1.50Si2.50 and (3) EuAg1.75Si2.25
.
Fig. 3. Lattice parameters of the solid solution of Si in EuAg2.
compound, which was prepared at 1000 ◦C in a corundum
crucible inside an evacuated quartz ampoule and reported in
[11], was not found at 400 ◦C.
alloy annealed at 1000 ◦C and reported in [9], was not ob-
served at 400 ◦C.
The results of X-ray LIII-absorption spectroscopy studies
of the valence of Eu in the compound EuAg2.00–1.25Si2.00–2.75
(Fig. 6) allow us to conclude that Eu has a stable valence 2+
over the whole homogeneity region. The temperature depen-
dence of the electrical resistance of EuAg2Si2 (Fig. 7) shows
a typically metallic behavior, ρ/ρ300 K increasing monotoni-
cally with increasing temperature. The thermoelectric power
In the system Eu–Ag–Si at 400 ◦C, the existence of the
compound EuAg2Si2 crystallizing with a CeAl2Ga2-type
structure was confirmed. Its homogeneity region was found
to be EuAg2.00–1.25Si2.00–2.75 (Fig. 4). The ternary AlB2-type
silicide in the Eu–Ag–Si system, already observed in earlier
works[10], isalsocharacterizedbyavariablecontentofsilver
and silicon, EuAg0.92–0.50Si1.08–1.50 (Fig. 5). The Eu4Ag2Si6
Fig. 4. Lattice parameters in the homogeneity region of the compound
Fig. 7. Temperature dependence of the relative resistance ρ/ρ300 K of
EuAg2.00–1.25Si2.00–2.75
.
EuAg2Si2.

B. Belan et al. / Journal of Alloys and Compounds 396 (2005) 212–216
215
Fig. 8. Temperature dependence of the thermoelectric power of EuAg2Si2.
Fig. 9. Temperature dependence of the inverse magnetic susceptibility of
EuAg2Si2.
Fig. 11. Phases formed in the systems (a) Eu–Ag–Si and (b) Eu–Cu–Si; 1 –
CeGa2Al2 type, 2 – AlB2 type, 3,4,5, and 6 – unknown structure.
(Fig. 8) and the magnetic susceptibility (Fig. 9) have been
determined for the same phase in the temperature region
77–450 K.
Among the chemical systems that are closely related to
those investigated here, the most thoroughly studied are the
systems Ce–Cu–Si [12] and Eu–Cu–Si [13]. A comparison of
the corresponding copper and silver systems (Figs. 10 and 11)
shows that by replacing copper by silver the number of phases
isreduced, from5to3fortheCe-containingsystemsandfrom
6 to 2 for the Eu-containing systems.
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