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168 CHEMICAL PROBLEMS 2021 no. 3 (19) ISSN 2221-8688
UDC 546.654.8.227
THE Bi2S3 - YbS SYSTEM O.M. Aliyev, T.F. Maksudova, D.S. Azhdarova, Sh.G. Mamedov, Sh.A. Gamidova
Acad. M. Nagiyev Institute of Catalysis and Inorganic Chemistry
National Academy of Sciences of Azerbaijan, H. Javid Ave. 113, Baku, AZ1143, e-mail: chemistry@science.az
Received 27.09.2021 Accepted 04.11.2021
Abstract: The phase equilibrium in the Bi2S3 - YbS system was studied by the methods of physicochemical analysis - DTA, XRD, MSA through measuring the micro-hardness and density, and a state diagram was plotted. It has been found that this system is a quasi-binary cross-section of the Yb-Bi-S ternary system. The formation of the two ternary compounds with YbBi2S4 and YbBi4S7 compositions was detected and the areas of solid solutions determined.
Keywords: system, eutectic, congruent, incongruent, state diagram, Bi2S3, YbS DOI: 10.32737/2221-8688-2021-3-168-172
Introduction
The obtaining of new promising materials with optical and thermoelectric properties is of great importance. One of the ways to obtain functional materials is to study phase equilibria in the systems based on already known binary compounds. Accordingly, the study of the Bi2S3-YbS system is of both scientific and practical interest due the starting, since the binary compounds have unique semiconductor properties [1-7].
The YbS compound melts congruently at 2403K and crystallizes in a cubic crystal system
with lattice parameters of unit cell: a = 5.694 A, the type of structure NaCl (space group Fm3m) [8].
Bi2S3 compound - melts congruently at 1048K and has a rhombic lattice of the Sb2S3 type with parameters: a = 11.15 A; b = 11.29 A; c = 3.98 A [9-11].
The purpose of this work is to plot a phase diagram of the state of Bi2S3 - YbS and study the physicochemical properties of the new discovered phases.
Experimental part
The study of the Bi2S3 - YbS system was carried out by methods of physicochemical analysis: differential thermal (DTA), X-ray diffraction (XRD), micro-structural (MSA) analyses, as well as by measuring the density and microhardness. The DTA curves have been recorded using an NTR-72 and "Termoskon 2" thermographs. Al2O3 was used as an etalon; the heating rate was 100/min. Diffraction patterns were recorded on a "D2 PHASER" X-ray diffractometer with CuKa radiation and a Ni filter. The micro-hardness was determined using a "Thixomet Smart Drive" micro-hardness tester at loads selected as a result of the micro-hardness studies into each phase. The MSA of
the polished etched thin sections was studied using an MIM microscope. The etchant was a chromium mixture (K2Cr2O7+concentrated HzSO4):H2O=1:1.
Alloys of the Bi2S3 - YbS system were synthesized both from the initial materials and the binary components of Bi2S3 and YbS. Elements were used for the synthesis of the alloys: Bi (B-4); Yb-ITM-1 (individual total more than 1) S-EC (sulfur extra clean). The samples were alloyed in sealed quartz ampoules, previously evacuated to a residual pressure of 10 Pa, in the temperature range 900-1500K. In order to obtain an equilibrium state, the homogenization annealing was performed at
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600-800 K for 700 h, depending on the composition.
Results and discussion
The state diagram of the Bi2S3 - YbS system was plotted due to the results of the study. It was found that two ternary compounds
have been formed in this system. The Bi2S3 -YbS system is quasi-binary and has a complex character (Fig. 1).
Figure 1. The state diagram of the cross section of Bi2S3 - YbS
The liquidus of the Bi2S3 - YbS system consists of branches of the primary crystallization of phases: a- phase based on Bi2S3, YbBi4Sy, YbBi2S4 and YbS compounds. The coordinates of the eutectic points between Bi2S3 and YbBi4S7 are as follows: 18 mol% YbS and 948K, and between YbBi4S7 and YbBi2S4 40 mol% YbS and 1023K. The Bi2S3 -YbS system can be conditionally represented as
two subordinate systems: Bi2S3 - YbBi4S7 and YbBi4S7 - YbS. The first subsystem belongs to the eutectic type. In the second subsystem, the YbBi2S4 ternary compound has formed according to the peritectic reaction. The liquidus of primary crystallization was roughly plotted in the concentration range of 8-100 mol% YbS. Nonvariant points of the Bi2S3-YbS system are shown in Table 1.
Table 1. Nonvariant points of the Bi2S3-YbS system
T.K. BiiSs mol% Solid phase Feature of the point
948 85 Bi2S3 - YbBi4S7 eutectic
1058 66.7 YbBi4S7 dystectic
1023 60 YbBi4S7 - YbBi2S4 eutectic
1088 50 YbBi2S4 peritectic
According to the DTA data, microstructural and X-ray diffraction analyses and the formation of two YbBi2S4 and YbBi4S7 compounds were established (Table 1). The YbBi2S4 compound melts incongruently at a temperature of 1088 K and is formed by the peretectic reaction: liq. + YbS YbBi2S4. The
YbBi4S7 compound melts congruently at 1058K.
According to the XRD data, in the concentration range 5-33.3 mol% of YbS, a (solid solutions based on Bi2S3) and YbBi4S7 co-crystallize, in the concentration range 33.3 mol% of YbS, YbBi4S7 and YbBi2S4 co-
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THE Bi2S3 - YbS SYSTEM
crystallize, and in the concentration range 50100 mol% of YbS, YbBi2S4 and YbS co-crystallize. Solid solutions based on bismuth sesqui-sulphide are locate in the concentration
According to the microstructural analysis, alloys containing 0-5; 33.3 m 50 mol% YbS are single phased. The formation of two ternary compounds in the system was also confirmed by plotting the dependence of H on composition X (Fig. 2).
The YbBi4S7 - a gray substance, stable in air, insoluble in water and in 10% of NaOH and KOH solutions weakly interacts with concentrated solutions of HCl and H2SO4.
The structure of the YbBi4S7 compound belongs to the stibnite type (Sb2S3) with
range of 0-5 mol% YbS at a room temperature, while at a eutectic temperature (948K) - in 8 mol% YbS. Solubility based on ytterbium monosulfide was not established.
rhombic lattice periods: a = 11.27; b = 15.07; c = 7.88 A, z = 5. The microhardness value is 1170 mPa, its pycnometric density and X-ray density (roentgenographic density) are 7.28 g/cm3 and 7.65 g/cm3, respectively. The YbBi2S4 - dark gray substance is stable in air, insoluble in water and alkalis. Mineral acids decompose it. YbBi2S4 and YbSb2S4 are isostructural and the first one crystallizes in the rhombic system with lattice parameters: a = 11.22; b = 14.75; c = 4.20 A, z = 4.
Table 2. Interplanar distances of Bi2S3, YbBi4S7, YbBi2S4 and YbS
Bi2S3 YbBi4S7 YbBi2S4 Y bS
dexp I/I0 dexp I/I0 dexp I/I0 dexp I/I0
6.650 20 5.6348 67 5.5928 39 6.5886 12
5.040 19 5.0246 30 4.9139 30 3.8557 8
3.970 38 3.9868 37 3.9576 34 3.2350 90
3.750 20 3.6972 17 3.6515 14 2.8302 100
3.560 94 3.5516 100 3.5516 100 1.9626 90
3.530 60 3.3663 12 3.3513 15 1.7108 53
3.256 18 3.2226 10 3.2457 18 1.6342 35
3.118 100 2.9895 59 3.0910 51
2.811 63 2.7956 20 2.8565 19
2.716 34 2.6907 12 2.7888 15
2.641 24 2.6292 10 2.7388 6
2.520 35 2.5064 36 2.6492 11
2.499 13 2.4546 13 2.5064 15
2.456 15 2.3516 12 2.4481 8
2.304 24 2.2475 33 2.3028 8
2.256 36 2.1697 7 2.2675 45
2.129 9 2.0790 13 2.1467 8
2.118 15 1.9795 10 2.0974 11
2.096 11 1.8929 20 1.9804 23
2.074 10 1.8716 27 1.9434 27
1.990 33 1.8424 7 1.8788 6
1.953 55 1.6979 19 1.8537 8
1.935 20 1.6760 7 1.6955 23
1.915 20 1.6240 6
1.884 14 1.5491 7
1.854 17
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Fig. 2. The dependence of micro-hardness on the composition for the Bi2S3 - YbS system
The microhardness is 2280 MPa, and the pycnometric density of YbBi2S4 is 6.75 g/cm3.
YbBi4S7 and YbBi2S4 compounds are p-type semiconductors (with holes).
Solid solutions obtained on the basis of
bismuth sesqui-sulphide are crystallized in the rhombic system. The periods of the unit cell of the solid solutions increase with an increasing of the YbS content: a = 11.13 - 11.18; b = 11.27 11.34; c = 3.97^4.02 Â.
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Bi2S3 - YbS SiSTEMi
O.M. dliyev, T.F. Maqsudova, D.S. djdarova, §.H. Mammadov, §.A. Hamidova
AMEA-nin akad. M.Nagiyev adina Kataliz vd Qeyri-uzvi Kimya institutu AZ 1143, Baki, H.Cavidpr., 113; e-mail: chemistry@,science. az
Fiziki-kimydvi analiz metodlari (DTA, RFA, MQA, mikrobdrkliyin vd sixligin tdyini) ild alinan ndticdldrd dsaslanaraq Bi2Se3-YbS sistemindd faza tarazligi oyrdnilmi§ vd onun hal diaqrami qurulmu§dur. Mudyydn edilmi§dir ki, sistem kvazibinar olub, YbBi2S4 vd YbBi4S7 tdrkibli uglu birld§mdldrin dmdld gdlmdsi ild xarakterizd olunur. YbBi4S7 1058 K-dd konqurient, YbBi2S4 isd inkonqurient (1088 K) driyir. Hdr iki birld§md ortorombik sinqoniyada kristalla§ir. Bi2S3-YbS sistemindd Bi2S3 dsasinda 8 mol% YbS tdrkibli bdrk mdhlul sahdsi a§kar edilmi§dir. YbS dsasinda isd praktiki olaraq hdllolma sahdsi mudyydn edilmdmi§dir. Agar sozlari: sistem, evtektika, konqruent, inkonqruent, hal diaqrami, Bi2S3, YbS.
СИСТЕМА Bi2Ss - YbS
О.М. Алиев, Т. Ф. Максудова, Д. С. Аждарова, Ш.Г. Мамедов, Ш.А. Гамидова
Институт катализа и неорганической химии им. акад. М. Нагиева Национальной АН Азербайджана, пр. Г. Джавида 113, Баку, AZ1143 Азербайджан e-mail: chemistry@,science. az
Методами физико-химического анализа (ДТА, РФА, МСА, измерением микротвердости и плотности) изучено фазовое равновесие в системе Bi2S3 - YbS и построена диаграмма состояния. Установлено, что данная система является квазибинарным сечением тройной системы Yb-Bi-S. В системе выявлено образование двух тройных соединений составa YbBi2S4 и YbBi4S7. Определены области твердых растворов.
Ключевые слова: система, эвтектика, конгруентное плавление, диаграмма состояния, Bi2S3, YbS.
