Phase Equilibria in Systems DyCuS2–EuS and Cu2S?Dy2S3?EuS

Article abstract of DOI:10.1134/S0036023618110141

The phase diagram of system DyCuS₂–EuS has been first constructed, and the phase equilibria in the Cu₂S–Dy₂S₃–EuS triangle at 970 K have been studied. Compound EuDyCuS₃ (1DyCuS₂ : 1EuS), space group Pnma, a = 10.1901(3) ?, b = 3.9270(1) ?, c = 12.8468(3) ?, melts incongruently at 1727 ± 7 K according to the reaction: EuDyCuS_3solid ? 0.17 SS EuS (90 mol % EuS, 10 mol % DyCuS₂) + 0.83 liq (42 mol % EuS, 58 mol % DyCuS₂), ΔH = 2.9 ± 0.6 kJ/mol; microhardness of the phase is 3080 ± 35 MPa. Compound EuDyCuS₃ is transparent in the range 3000–1800 cm^–1. In system DyCuS₂–EuS, the solid solution (SS) based on EuS extends from 91 to 100 mol % at 1770 K and from 92 to 100 mol % at 1170 K. In γ-DyCuS₂, 2 mol % EuS dissolves at 1487 K. The eutectic is formed between compounds DyCuS₂ and EuDyCuS3 at 12 mol % EuS, T = 1487 ± 8 K. In system Cu₂S?Dy₂S₃?EuS, 10 secondary systems have been isolated. At 970 K, tie-lines are located between compound EuDyCuS₃ and solid solutions based on compounds β-Cu₂S, EuS, DyCuS₂, β-(DyCu₃S₃), and EuDy₂S₄; between DyCuS₂ and the solid solution of α-Dy₂S₃, DyCuS₂, and EuDy₂S₄.

Full text of DOI:10.1134/S0036023618110141

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2018, Vol. 63, No. 11, pp. 1494–1500. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © A.V. Ruseikina, O.V. Andreev, 2018, published in Zhurnal Neorganicheskoi Khimii, 2018, Vol. 63, No. 11, pp. 1476–1482.
PHYSICOCHEMICAL ANALYSIS
OF INORGANIC SYSTEMS
Phase Equilibria in Systems DyCuS2–EuS
and Cu2S−Dy2S3−EuS
A. V. Ruseikinaa, * and O. V. Andreeva
aTyumen State University, Tyumen, 625003 Russia
*e-mail: adeschina@mail.ru
Received January 18, 2018
Abstract⎯The phase diagram of system DyCuS2–EuS has been first constructed, and the phase equilibria in
the Cu2S–Dy2S3–EuS triangle at 970 K have been studied. Compound EuDyCuS3 (1DyCuS2 : 1EuS), space
group Pnma, a = 10.1901(3) Å, b = 3.9270(1) Å, c = 12.8468(3) Å, melts incongruently at 1727 7 K accord-
ing to the reaction: EuDyCuS3solid ↔ 0.17 SS EuS (90 mol % EuS, 10 mol % DyCuS2) + 0.83 liq (42 mol %
EuS, 58 mol % DyCuS2), ∆H = 2.9 0.6 kJ/mol; microhardness of the phase is 3080 35 MPa. Compound
EuDyCuS3 is transparent in the range 3000–1800 cm–1. In system DyCuS2–EuS, the solid solution (SS)
based on EuS extends from 91 to 100 mol % at 1770 K and from 92 to 100 mol % at 1170 K. In γ-DyCuS2,
2 mol % EuS dissolves at 1487 K. The eutectic is formed between compounds DyCuS2 and EuDyCuS3 at
12 mol % EuS, T = 1487 8 K. In system Cu2S−Dy2S3−EuS, 10 secondary systems have been isolated. At
970 K, tie-lines are located between compound EuDyCuS3 and solid solutions based on compounds β-Cu2S,
EuS, DyCuS2, β-(DyCu3S3), and EuDy2S4; between DyCuS2 and the solid solution of α-Dy2S3, DyCuS2,
and EuDy2S4.
Keywords: phase equilibria, incongruent melting, complex sulfides, microstructural analysis, differential
scanning calorimetry
DOI: 10.1134/S0036023618110141
Dy3+ and exhibits a ferrimagnetic transition at 5.3 K
Compounds EuLnCuS3 (Ln = Gd–Lu) are non-
metallic magnetic materials [1, 2]. Phase diagrams of [1, 2].
systems Cu2S–Ln2S3–EuS (Ln = La, Nd) con-
structed allowed us to select conditions for the prepa-
ration of crystals of incongruently melting compounds
EuLnCuS3 directly from melt [3]. A similarity of phase
equilibria was determined in Cu2S–Ln2S3–EuS sys-
tems formed by elements of the cerium subgroup [4].
In system Cu2S–Dy2S3, complex sulfides DyCuS2
[7–10] and DyCu3S3 [8, 11, 12] are formed, which
exist as three polymorphous modifications. Com-
pound α-DyCuS2 has an orthorhombic crystal struc-
ture, space group Pnma, ST 2 [13], the unit cell param-
eters are a = 13.4251 Å, b = 3.9796 Å, c = 6.2743 Å [9];
α-DyCuS2 undergoes polymorphic transitions
α-DyCuS2 → β-DyCuS2 at 1175 K and β-DyCuS2 →
γ-DyCuS2 at 1260 K. High-temperature polymorphs
are not recorded by quenching [8]. The DyCu3S3
phase of the berthollide type has a shallow maximum
of melting at 1590 K and a composition of 37 mol %
Dy2S3 [8, 14]. The coordinates of the eutectic between
the Cu2S and DyCu3S3 phases are 1.3 mol % Dy2S3,
T = 1390 K [8]. In system Cu2S–EuS, a eutectic is
As far as we know, phase equilibria have not been
studied in systems Cu2S–Ln2S3–EuS (Ln = Gd–Lu).
Dysprosium Dy (4f105d06s2) exhibits a stable valence
of 3; it is a typical rare-earth element of the yttrium
subgroup [5], which allows us to consider the Cu2S–
Dy2S3–EuS system as a model.
In system Cu2S–Dy2S3–EuS, compound EuDy-
CuS3 (1Cu2S : 1Dy2S3 : 2EuS) is formed. Samples
were obtained by the solid-phase reaction by heating a
stoichiometric mixture of rare-earth sesquioxides formed between the initial sulfides at 24.5 mol % EuS,
Ln2O3 and copper oxide CuO in a graphite boat at T = 1069 K [3, 4]. In the Dy2S3–EuS system, com-
1170–1320 K in a flow of a CS2 and N2 gas mixture [2]. pound EuDy2S4 is observed to form with the orthor-
The crystals of EuDyCuS3 belong to the orthorhom- hombic crystal system, ST CaV2O4, space group
biccrystal system, the structural type (ST) Eu2CuS3 Pnma; unit cell parameters are a = 11.87 Å, b = 3.94 Å,
c = 14.17 Å [15–17]. Compound EuDy2S4 melts
[6], space group Pnma, the unit cell parameters are
a = 10.1904(3) Å, b = 3.9267(1) Å, c = 12.8471(4) Å incongruently at 2150 40 K according to the scheme:
[2]. Compound EuDyCuS3 contains magnetic ions EuDy2S4 ↔ SS EuS + liq. The extent of solid solutions
1494

PHASE EQUILIBRIA IN SYSTEMS DyCuS2–EuS
1495
(SS) based on EuS and γ-Dy2S3 at 1770 K is 9 mol % the Setsoft Software 2000 program package when per-
forming the linear baseline from the first to the last
point and fixed as the point of intersection of the tan-
gent line with the baseline.
Dy2S3 and 8 mol % EuS, respectively [18].
Phase equilibria in the quasi-triple system Cu2S–
Dy2S3–EuS were studied in the Cu2S–EuDyCuS3
section [19]. The Cu2S−EuDyCuS3 system is of
eutectic type with the eutectic coordinates of 10 mol %
EuDyCuS3, T = 1191 K. On the basis of β-Cu2S,
a solid solution of the open type is formed with a peri-
tectic point in the coordinates of 4 mol % EuDyCuS3,
T = 1248 K [18].
The phase diagram of the DyCuS2–EuS section
has not been studied. The mass balance equations of
the phases involved in the invariant transformations
have not been compiled. There are no data on the
enthalpies of phase transformations. Triangulation of
the triple system Cu2S−Dy2S3−EuS has not been car-
ried out. The study of phase equilibria in the system
Cu2S−Dy2S3−EuS will allow one to determine the
intervals of compositions and temperatures for obtain-
ing samples of compound EuDyCuS3 by crystalliza-
tion from the melt.
IR spectroscopic studies of compound EuDyCuS3
were carried out on an FT-IR spectrometer in the
range 4000–400 cm–1. The polycrystalline sample was
ground in an agate mortar and mixed with powder
potassium bromide an annealed at 720 K to a homoge-
neous mass [23, 24]. The mixture was placed in a PF13
mold and pressed into a pellet using an Autotouch
hydraulic press with a force of 8 tons; loading time was
4 min.
Microstructural analysis of the polished samples
was carried out on an Axio Vert.A1 microscope; duro-
metric analysis (DMA) was performed on an HMV-
G21 device using the Vickers method with an error not
exceeding 1.5%. Holding time, 15 s; load, 10 kG (98.07 N).
Graphical constructions were performed using the
Edstate 2D and Edstate 3D programs. X-ray powder
diffraction data was obtained on a Dron-7 and a D2
1
Phaser diffractometers equipped with a Lynxeye
The aims of this work are to construct a phase dia-
gram of system DyCuS2–EuS, determine the enthalp-
ies of phase transformations in the system, and study
phase equilibria in the Cu2S−Dy2S3−EuS triangle.
detector (CuKα radiation, Ni-filter). Samples were
prepared by grinding in an agate mortar with ethane
added. The unit cell parameters of the lower crystal
systems were determined using the ITO program [25].
EXPERIMENTAL
RESULTS AND DISCUSSION
Compound Cu2S was obtained from elementary
Cu (special purity grade 11-4) and elemental S (special
purity grade 15-3) in sealed evacuated quartz tubes [3,
4]. Sulfides Dy2S3 and EuS were synthesized from
appropriate oxides (DiO-L and EvO-Zh grade,
respectively) in a flow of H2S and CS2 at 1300 K [20].
According to X-ray powder diffraction analysis, the
sulfides obtained are single-phase and have a stoichio-
metric composition within the error of the chemical
analysis. In system Cu2S–Dy2S3–EuS, 80 samples of
the inner part of the concentration triangle of sulfides
Cu2S, EuS, and Dy2S3 were synthesized according to
the previously described procedures [21]. The samples
were annealed in evacuated sealed quartz ampules at
The phase diagram of system DyCuS2–EuS is first
constructed showing complex sulfide EuDyCuS3 to be
formed. The X-ray powder diffraction pattern of com-
pound EuDyCuS3 is indexed on the basis of a orthor-
hombic crystal system, ST Eu2CuS3, space group
Pnma; the unit cell parameters are a = 10.1901(3) Å,
b = 3.9270(1) Å, c = 12.8468(3) Å (Fig. 1a), which
agrees with the data reported [2]. The structure of com-
pound EuDyCuS3 is described by two-dimensional layers
(DyCuS3) in the ba plane formed by distorted CuS4 tetra-
hedra and DyS6 octahedra with ions Eu2+ residing
between the layers. In the temperature range 770–1170 K,
the structural type of compound EuDyCuS3 remains
970 K for 3000 h and at 1170 K for 1440 h. The anneal- unchanged, which corresponds to the theoretical idea
ing temperature in the muffle furnaces was set with a
of the presence of dysprosium in the region of crystal-
Thermolux thermostat with the accuracy of 5 K. At lochemical stability [26]. The crystals of complex sul-
1770 K, the samples were annealed for 30 min in an fide EuDyCuS
3 have a gray-brown color, H = 3080
35 MPa. Compound EuDyCuS3 is transparent for IR
open reactor with induction heating of a graphite cru-
cible. The results of X-ray powder diffraction, micro-
structural analysis, and DSC samples in the course of
annealing make it possible to conclude that an equilib-
rium state was reached.
DSC was performed on a Setsys Evolution 1750
device (TGA–DSC 1600). Recording conditions: a
PtRh 6%–PtRh 30% DSC sensor, heating rate 5 K/min,
argon purge rate 25 mL/min, crucible volume 100 μL,
sample weight 100–110 mg [22]. The temperature of
the beginning of heat absorption was determined using
radiation in the range 3000–1800 cm–1 (Fig. 1b), which
is typical for EuLnCuS3 compounds [27]. Absorption
bands are observed in the ranges 3800–3000 and
1700–1400 cm–1 attributed to stretching and bending
vibrations of hydroxyl groups. The presence of water
sorbed can be caused by the water sensitivity of powder
EuDyCuS3.
1
The studies were carried out at the Earth Cryosphere Institute,
Siberian Branch of the Russian Academy of Sciences (Tyumen).
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1496
RUSEIKINA, ANDREEV
(а)
I1/2
a
c
DyS6
2
CuS4
Eu
1
10
15
20
25
30
35
2θ, deg
40
45
50
(b)
(c)
T, %
TG
DSC
20
10
0
1568
1543
80
60
40
20
1500
2
1727
1
–10
1450 1500 1550 1600 1650 1700 1750
3500 3000 2500 2000 1500 1000
ν, cm–1
T, К
Fig. 1. Panel (a): (1) Experimental X-ray powder diffraction pattern and (2) the [010] projection of the EuDyCuS structure.
3
Panel (b): IR spectrum of EuDyCuS annealed at 970 K. Panel (c): differential thermal curves for EuDyCuS .
3
3
Three thermal events are observed on the DSC Similar polymorphic transitions were found to exist in
isostructural compound SrDyCuS3 [22].
curves of the EuDyCuS3 samples (Fig. 1c, Table 1),
which are completely reproduced in the heating–
cooling cycles. When the sample is heated after the last
thermal event, the sample is in a polycrystalline state,
the appearance of a liquid phase in the sample was not
detected. The thermal effects are reproduced in the
region 17–80 mol % EuS at the same temperatures as
in the EuDyCuS3 sample and in the Cu2S–EuDyCuS3
section [19]. The fixed thermal events are caused by
phase transitions of the first kind, namely, the poly-
morphous transformations of EuDyCuS3. High-tem-
perature modifications of EuDyCuS3 are not fixed by
Compound EuDyCuS3 melts at temperatures close
to the liquidus of system DyCuS2–EuS (Fig. 2). The
peaks of the thermal events of incongruent melting of
compound EuDyCuS3 and melting of EuS crystals are
superimposed upon heating (Fig. 3). When the sam-
ples are cooled immediately after the thermal event of
the beginning of crystallization of the EuS phase
appeared, the peak of EuDyCuS3 crystallization is
manifested explicitly. According to the data of heating
and cooling, the average temperature of the incongru-
ent melting of compound EuDyCuS3 is taken equal to
the quenching method (cooling rate ~103–104 K/min). 1727 7 K. The equation of the material balance of
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PHASE EQUILIBRIA IN SYSTEMS DyCuS2–EuS
1497
Table 1. Mass balance equations for the phases participating in invariant transformations in system DyCuS2–EuS
Coordinates
of invariant points
ΔHmelt
kJ/mol
,
Phase transformation
Mass balance equations
composition
T, K
Incongruent melting
of compound
EuDyCuS3
(1DyCuS2 : 1EuS)
1727 EuDyCuS3solid (50 mol % EuS; 50 mol % DyCuS2) ↔
0.17SS EuS (90 mol % EuS; 10 mol % DyCuS2) +
0.83liq (42 mol % EuS; 58 mol % DyCuS2)
(2.9)
Melting of the eutectic 12 mol % EuS
1487 0.79DyCuS2 (2 mol % EuS; 98 mol % DyCuS2) +
0.21EuDyCuS3 (50 mol % EuS; 50 mol % DyCuS2) ↔
liq (12 mol % EuS; 88 mol % DyCuS2)
7.6 0.8
4.4 0.5
1.0 0.1
2.0 0.2
Polymorphic transition EuDyCuS3
1500 EuDyCuS3solid (50 mol % EuS; 50 mol % DyCuS2) ↔
0.48SS EuS (91 mol % EuS; 9 mol % DyCuS2) +
0.52liq (12.5 mol % EuS; 87.5 mol % DyCuS2)
α-EuDyCuS3 ↔
β-EuDyCuS3
(1DyCuS2 : 1EuS)
Polymorphic transition EuDyCuS3
1543 EuDyCuS3solid (50 mol % EuS; 50 mol % DyCuS2) ↔
0.46SS EuS (90.8 mol % EuS; 9.2 mol % DyCuS2) +
0.54liq (15.5 mol % EuS; 84.5 mol % DyCuS2)
β-EuDyCuS3 ↔
γ-EuDyCuS3
(1DyCuS2 : 1EuS)
Polymorphic transition EuDyCuS3
1568 EuDyCuS3solid (50 mol % EuS; 50 mol % DyCuS2) ↔
0.45SS EuS (90.5 mol % EuS; 9.5 mol % DyCuS2) +
0.55liq (17 mol % EuS; 83 mol % DyCuS2)
γ-EuDyCuS3 ↔
δ-EuDyCuS3
(1DyCuS2 : 1EuS)
the phases participating in the invariant transforma- pound DyCuS2 and melting of crystals Dy2S3 are
tion is shown in Table 1.
Compound DyCuS2 melts incongruently at 1587 K.
The thermal events of incongruent melting of com-
superimposed on the heating curve but resolved on the
cooling curve. The melting enthalpy of compound
DyCuS2 was determined to be ∆H = 11.9 2 kJ/mol.
T, K
2520
1
2
3
L
EuDyCuS3
1900
1900
L + SS EuS
91%
1727
42%
L + Dy2S3
90%
DyCuS2 + L
EuS
δ-EuDyCuS3 + SS
L + δ-EuDyCuS3
1568
1543
1500
90.5%
1587
12%
90.8%
91%
1500
1100
1500
1487
γ-EuDyCuS3 + SS EuS
β-EuDyCuS3 + SS EuS
L + γ-Dy2S3 + γ-DyCuS2
γ-DyCuS2 + α-EuDyCuS3
SS
EuS
1239
1167
1251
β-DyCuS2 + α-EuDyCuS3
1174
1100
92%
α-EuDyCuS3 + SS EuS
93%
α-DyCuS2 + α-EuDyCuS3
DyCuS2
EuS
20
40
mol %
60
80
Fig. 2. Phase diagram of the DyCuS –EuS system: (1) DSC data, (2) single-phase sample, and (3) two-phase sample (according
2
to X-ray powder diffraction pattern and microscopic analysis).
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1498
RUSEIKINA, ANDREEV
The thermal events of polymorphic transformations
are recorded: α-DyCuS2 ↔ β-DyCuS2 at 1174 K, ΔH =
1.44 kJ/mol; β-DyCuS2 ↔ γ-DyCuS2 at 1251 K, ΔH =
0.41 kJ/mol. The temperatures of polymorphic transi-
tions are consistent with the results of [8]. According
to DSC, a decrease in the temperature of the polymor-
phic transitions α ↔ β to 1167 2 K and β ↔ γ to 1239
2 K was recorded in the samples of compositions 5–
30 mol % EuS, which indicates the eutectoid phase
transformations in the solid solution based on com-
pound DyCuS2. In γ-DyCuS2, 2 mol % EuS dissolves at
1487 K.
1174
1251
–40
–60
1587
DyCuS2
1167
1168
1168
1237
1239
1236
1482
1490
–40
–60
5 mol %
7 mol %
1590
1499
1544
13 mol %
52 mol %
Т, К
1515
1539
1571
A region of solid solution is formed on the base of
EuS, the extent of which depends on the temperature
being 91–100, 92–100, and 93–100 mol % EuS at
1770, 1170, and 970 K, respectively. The decrease in
the unit cell parameter for the EuS phase from a =
5.967 Å to a = 5.951 Å at 970 K is consistent with the
value of the reduced radius r(Cu+, Dy3+) = (0.600 +
–40
–20
1495
1200 1300 1400 1500 1600
0.912)/2 = 0.756 Å for cations replacing the Eu2+ ions
Fig. 3. Differential thermal curves for samples of system
DyCuS –EuS. The compositions of the samples are
2
2+
(
= 1.17 Å, CN = 6) in the EuS structure [28].
expressed in mol % EuS.
rEu
A negative deviation from Vegard’s law indicates that
the interaction force between the components of the
EuS matrix is less than the interaction force between
sulfur anions and doping cations [29, 30].
DyCuS2, EuDy2S4, SS β-DyCu3S3. The positions of
the tie-lines in the triangle are indicated (Fig. 4). The
following phases also exist in equilibrium: DyCuS2–
SS α-Dy2S3, DyCuS2–EuDy2S4. The position of the
tie-lines in the ternary Cu2S–Dy2S3–EuS system
makes it possible to separate 10 secondary systems:
EuS–EuDyCuS3–Cu2S (I), compositions from the
region SS β-Cu2S–EuDyCuS3 (II), Cu2S–EuDy-
An eutectic is formed between the DyCuS2 and
EuDyCuS3 phases, the melting peak of which is fixed
in 15 samples of various compositions at 1487 8 K.
According to the microscopic analysis and the con-
struction of the Tammann triangle, the composition
of the eutectic is 12 mol % EuS. The equation of the
material balance of the phases participating in the CuS3–β-DyCu3S3 (III), compositions from the
invariant transformation was derived (Table 1). The
liquidus line in the DyCuS2–eutectic region was con-
structed by approximating the DSC data by polynomi-
als of the second and third degree.
region SS β-DyCu3S3–EuDyCuS3 (IV), β-DyCu3S3–
EuDyCuS3–α-DyCuS2 (V), α-DyCuS2–EuDy2S4–
EuDyCuS3 (VI), α-DyCuS2–α-Dy2S3–EuDy2S4
(VII), α-DyCuS2–compostions from the region SS
α-Dy2S3 (VIII), EuS–EuDy2S4–EuDyCuS3 (IX), com-
positions from the region SS EuS–EuDyCuS3 (X).
In the region of 50–100 mol % EuS at temperatures
below the incongruent decomposition temperature of
compound EuDyCuS3, phases EuDyCuS3 and a EuS-
base solid solution are in equilibrium. Only reflections
of conjugated phases are observed on the X-ray pow-
der diffraction patterns of the samples annealed.
According to microstructure analysis of samples of
different chemical compositions, there are brown oval
EuS grains sized from 10 × 30 to 75 × 120 μm located
in the EuDyCuS3 phase field. The liquidus branch in
the range 42–100 mol % EuS was approximated by a
polynomial of the third degree. There is a negative
deviation from the linear dependence.
In system DyCuS2–EuS, primary formed crystals
of compound EuDyCuS3 are observed in the samples
with the composition 13–41 mol % EuS crystallized
from melt.
In the quasi-triple system Cu2S–Dy2S3–EuS at
970 K, complex sulfide EuDyCuS3 is in equilibrium
with the following phases: SS β-Cu2S, SS EuS,
The phase equilibria in the polythermal sections of
the ternary system are characterized.
System DyCuS2–EuDy2S4 is of the eutectic type.
The thermal event of melting of the eutectic was found
at 1515 3 K. The change in the unit cell parameters
of compound DyCuS2 from a = 13.425 Å, b = 3.979 Å,
c = 6.274 Å to a = 13.420 Å, b = 4.007 Å, c = 6.256 Å
indicates a solid solution based on DyCuS2 to exist.
The temperatures of the eutectoid transformations in
the region of the solid solution of DyCuS2 were recorded
to be 1167 1 and 1245 2 K. The microhardness of the
EuDy2S4 phase grains is 3400 40 MPa.
In system EuDyCuS3–EuDy2S4 at 970 K, phases
EuDyCuS3 and EuDy2S4 are in equilibrium. Changes
in the unit cell parameters of the conjugated phases in
the two-phase region were not found.
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PHASE EQUILIBRIA IN SYSTEMS DyCuS2–EuS
1499
Dy2S3
VIII
VII
VI
V
IV
IX
III
I
II
24.5%
β-Cu2S + SS EuS
1069
Cu2S
EuS
1470
β-Cu2S + L
1186
γ-Cu2S + L
L + SS EuS
L
1970
2470
T, K
Fig. 4. Positions of the tie-linetie-lines in system Cu S−Dy S −EuS at 970 K. The dots indicate the samples studied; the Roman
2
2 3
numerals indicate the secondary systems.
In the sections of the ternary system Cu2S–Dy2S3– EuLnCuS3 and solid solutions based on phases of the
EuS, the eutectic temperature decreases regularly systems forming a triangle are in equilibrium. We
from the high-temperature part of the system to the should expect similarity of phase equilibria in all sys-
low-temperature part: 1515 K (system DyCuS2– tems Cu2S–Ln2S3–EuS (Ln = Gd–Lu).
EuDy2S4) → 1487 K (system DyCuS2–EuDyCuS3) →
1480 K (secondary system V) → 1469 K (system
ACKNOWLEDGMENTS
DyCu3S3–EuDyCuS3) → 1400 K (secondary system IV,
composition 60Cu2S : 24.8Dy2S3 : 15.2EuS) → 1363 K
(secondary system IV, composition 69.7Cu2S :
The authors are grateful to Zh.A. Demchuk, the
deputy head of the testing laboratory of the Tyumen
20.4Dy2S3 : 9.9EuS) → 1191 K (system Cu2S–EuDy- section of quality control, metrology, and electrome-
try of Gazpromneft’ Krasnoyarsk, for microstructural
and X-ray powder diffraction analysis of samples of
the ternary system.
CuS3). It is possible that the point of the triple eutectic is
shifted to the eutectic in the Cu2S–EuDyCuS3 system.
Similar phase equilibria are observed in system
Cu2S–Gd2S3–EuS [18] and system Cu2S–Dy2S3–
EuS. Isostructural compounds EuGdCuS3 and
EuDyCuS3 are formed in the systems, in which such
high-temperature polymorphic transitions are fixed;
the compounds melt incongruently. In systems
LnCuS2–EuS, a complex sulfide and a eutectic are
formed. In ternary systems at 970 K, compounds
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2018