A.V. Ruseikina, V.A. Chernyshev, D.A. Velikanov et al.
Journal of Alloys and Compounds 874 (2021) 159968
ferromagnetics [28,29], ferrimagnetics [28,30], paramagnetics [1]
and diamagnetics [32]. The compounds are semiconductors with
bandgap energy from 1.63 eV to 2.61 eV [1,12,26,40,42,44]. The
europium-containing compounds possess narrower bandgap energy
that is associated with the presence of 4f-5d-transition in Eu2+ ion
demonstrating ability to control bandgap energy of chalcogenides
The X-ray diffraction measurements were performed by means of
an X-ray diffractometer PANalytical X'Pert PRO equipped with the
detector PIXcel (Co Kα-emission, graphite monochromator) and
DRON 7 (CuKα-emission and Ni filter) at 298 K. The X-ray diffraction
patterns were scanned at 298 K over the diffraction angles
o
10º≤ 2θ≤ 125(140)º in the increments of 0.013 and total accumula-
tion time 13 h. The crystal structures of the whole series of EuLnCuS
3
due to the embedded Eu [44]. PbLaCuS
3
possesses the conductivity
of p-type with the projected bandgap energy ≈1.5 eV [32]. The qua-
ternary chalcogenides are of various melting types like congruent
were previously refined in terms of the powder data by the deriva-
tive difference minimization method (DDM) and Rietveld method
[28,44,63], and the X-ray analysis was performed to determine
chemical composition and the phase purity of the synthesized
samples, that is important for the measurements of thermal, optical
and magnetic properties. According to the X-ray diffraction analysis,
the structural type of the compounds and the unit cell parameters
were consistent with the earlier data [28,44,63].
[52–55] and incongruent [26,30,44,49,56,57] ones. The phase equi-
libria in multicomponent systems Сu
2
2 3
Х–AX–B X
[49–55,58–60]
have complex nature, including peritectic, eutectic, eutectoid, peri-
tectoid interactions and formation of extensive solid solution areas.
The compounds ALnCuS
structural types of the orthorhombic system [26–28,30–33,40–42,
4,45,49,50,53,57,61–71]; see this table SI in Supplementary
Information for more detail.
Sulfides EuLnCuS (Ln = La-Nd, Gd, Dy-Er) melt incongruently
and three polymorphous transitions in the temperature range of
400–1610 K were detected for some of them [30,57,58]. The tran-
sition into the ordered magnetic state for EuLnCuS (Ln = Y, Eu, Tb,
Dy, Er-Lu) compounds occurs in the narrow temperature range from
3
(A = Sr, Ba, Eu, Pb) crystallize in four
4
The microstructure was observed on polished samples using the
AxioVert.A1 and Olympus GX-71 microscopes. Scanning electron
microscopy (SEM) was performed on a Philips SEM 515 and
JEOLJSM-6510 LV equipped with an energy dispersive spectrometer.
The differential scanning calorimetry experiments were carried
out on a Setsys Evolution 1750 (TG–DSC 1600) with the aid of the
PtRh 6%-PtRh 30% thermocouple. The complex was calibrated ac-
cording to the data of melting temperatures and melting enthalpies
of standard substances (Sn, Pb, Zn, Al, Ag, Au, Сu, and Pd). Prior to an
experiment, the working chamber of the complex was evacuated
and then filled with argon. The recording parameters were the fol-
lowing: the sample size: 100–110 mg, heating rate: 5 K/min, argon
flow rate: 25 ml/min, and alundum crucible capacity: 100 µl. The
heat absorption onset temperature was determined as the inter-
section point of a tangent with the baseline in the program package
Setsoft Software 2000 with a linear baseline from the first to last
point. The temperatures and enthalpies of the thermal events ap-
pearing in replica measurements were aligned with the thermo-
analytical error bar. While performing thermal analysis up to 1840 K,
the samples transformed into melt. The TG curves showed a 0.16 wt%
3
1
3
3
.4 to 5.5 K [28–30].
Despite the fact that the structure of the compounds EuLnCuS
3
(
Ln = La-Lu) was actually solved and refined previously, the data
concerning their properties and physicochemical characteristics are
still incomplete. This restricts the potentialities of their practical use.
The aim of this work is a comprehensive study of the compounds
3
EuLnCuS (Ln = La-Lu), in particular, the experimental determination
of thermal, optical, magnetic, durometric properties, the perfor-
mance of ab initio calculations of crystal structures, phonon spectra,
elastic properties, and the determination of regularities in their
property changes depending on rLn3+
.
2. Materials and methods
3
weight loss in the samples of EuLnCuS (Ln = Tb, Tm, Yb, Lu).
The graphical plottings were acquired by means of the program
Edstate 2d [72]. The crystal structures were visualized in the soft-
ware package Diamond 3 [73].
Durometric analysis of a polished sample was performed by the
Vickers method on an HMV-G21 [74]. The samples were used in the
cylindrical form and poured over with epoxy glue (EP resin and
solidifier in the ratio 100:12). Then, they were smoothed, and finally
polished by GOI polishing paste. The exposure time was 15 s and the
load was 10 kg-force (98.07 N).
2
.1. Materials
The rare-earth element oxides Ln
2
O
3
(Ln = La, Nd, Sm, Gd, Dy-Lu),
2 4 7
LnO (Ln = Ce, Pr) and Tb O (99.9%) were procured at the manu-
facture of Uralredmet (Russia). Elementary sulfur (99.99%) was
purchased in the Komponent-reactive manufacture (Russia).
Elementary copper (99.99%) was procured in Red Chemist, Ltd.
(
Russia). Argon (99.998%) was purchased from the technical gases
manufacture Kislorod-servis (Russia). Epoxy glue was procured in
OOO Scientific-Industrial Complex “Astat” (Russia). GOI polishing
paste was purchased in OOO “Tehnopayka” (Russia).
The low-temperature (1.8–50 K) magnetic susceptibilities of
EuLnCuS
magnetometer [75–77] in a 10 Oe magnetic field. Masses of the
samples were 0.0862 g (EuLaCuS ), 0.0475 g (EuCeCuS ), 0.1025 g
(EuPrCuS ), 0.0655 g (EuNdCuS ), 0.1055 g (EuSmCuS ), 0.0786 g
EuHoCuS ).
The dilatometric analysis was performed by means of a DIL 402
3
(Ln = La, Сe, Pr, Nd, Sm, Ho) were studied on a SQUID
3
3
2
.2. Methods
3
3
3
(
3
The compounds EuLnCuS
3
were synthesized by melting the in-
: 1Cu S. The
S was prepared from Cu and S by the ampoule
method according to the technique described earlier [49]. The
compounds EuS, Ln were synthesized at 1300 K from the rare-
earth element oxides in the flow of Н S and СS2, produced by de-
composition of аmmonium rhodanide (the carrier gas is argon) [30].
The powdered batch composed оf 2EuS: 1Ln :1Cu S was molten in
termediate sulfides mixed in the ratio 2EuS: 1Ln
compound Cu
S
2 3
2
РC in the following conditions: the temperature range for mea-
surements was 300–1240 K, heating rate was 5 K/min, pressure of
the puller contact was 30 сН, purge speed of argon was 25 ml/min.
The measurements were performed on the tablet with the diameter
2
2 3
S
2
0
of 6 mm and 1.28–3.3 mm thick. The initial length L of the samples
–3
was determined with the absolute error ± 5·10 mm, while per-
centage error of the initial length measurement is within the range
of 0.15–0.4%. The percentage error of the measurements of elonga-
tion ΔL during the thermal dilatation process was 5%, and the per-
S
2 3
2
the argon atmosphere in a graphite crucible placed in the silica
reactor. The synthesized samples were annealed in evacuated
and sealed-off silica glass ampoules at 1170 K for 1500 h [63]. No
interaction of the samples with silica was found during annealing.
0
centage error ΔL/L ranged from 5.15% to 5.4%. The dependencies of
the relative elongation of the samples on the temperature were
2