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CHEMICAL PROBLEMS 2020 no. 2 (18) ISSN 2221-8688
UDC 546 (72.681.682.22)
FeS- FeGa2S4- FeGaInS4 SYSTEM
F.M. Mammadov
Institute of Catalysis and Inorganic Chemistry National academy of Sciences of Azerbaijan H. Javid ave., 113, AZ-1143, Baku, Azerbaijan e-mail: _faikmamadov@mail.ru
Received 22.01.2020 Accepted 01.04.2020
Abstract: The phase equilibria in the FeS-FeGa2S4-FeGaInS4 system were studied using the differential thermal and X-ray diffraction phase analysis. The projection of the liquidus surface and the isothermal sections of the phase diagram at 1200 and 900 K were constructed. It revealed that it belongs to quasi-ternary systems with monovariant eutectic and peritectoid equilibria. At 1200 K, the system was characterized by the presence of a continuous series of solid solutions along the boundary system FeGa2S4-FeGaInS4 (fi-phase) as well as solid solutions based on the high-temperature modification FeS (a-phase) which formed a wide two-phase region a + fi. The FeS-FeGa2S4 boundary system was characterized by the formation of the Fe2Ga2S5 ternary compound at 900 K. This compound formed Fe2Ga2S5+fi and Fe2Ga2S5+ a+fi heterogeneous regions below this temperature which significantly narrowed the two-phase region a + fi.
Keywords: FeGa2S4, FeS, FeGaInS4, phase diagram, liquidus, solid solutions DOI: 10.32737/2221-8688-2020-2-214-221
Introduction
Compounds of AB2X4- type (A-Mn, Fe, Co, Ni, Ge, Sn, Pb, B-p1 or p3-element, X-chalcogen) and phases based on them are valuable functional materials with thermoelectric, photoelectric, optical, magnetic and other properties [1-8]. In recent years, it has been established that some compounds of this type with a layered structure such as tetradimite are topological insulators and extremely promising for practical applications, ranging from spintronics to safety systems and medicine [9-13]. It is known that the intensive development of a new scientific field -spintronics is associated with the possibility of transferring the oriented electron spin from a ferromagnet to a semiconductor. The above compounds also apply to materials promising for the specified area [14-16]. In [17, 18] published recently, the MnBi2Te4 compound, the first antiferromagnetic topological insulator, was described.
The development and optimization of the synthesis of new complex phases are based on data on phase equilibria and thermodynamic
characteristics of the corresponding systems [19-24].
The paper explores phase relations in the FeS- FeGa2S4-FeGaInS4 system. The initial compounds of this system were studied thoroughly.
The FeS compound melt congruently at 1461 K and undergo polymorphic transitions at 411 and 588 K [25]. The high-temperature modification of FeS crystallized in a tetragonal structure (Sp.gr.P4/nmm) with lattice parameters a = 0.3768 nm, c = 0.5039 nm [26] or a = 0.36735 nm, c = 0.50328 nm [27], while the low-temperature modification has a hexagonal structure: a = 0.34436 (1) nm, c = 0.57262 (2) nm [28].
According to [29], the ternary compound FeGa2S4 melts congruently at 1418 K. According to [30], it is formed by the peritectic reaction at 1343 K and undergoes a polymorphic transformation at 1283 K. In [31] it was shown that FeGa2S4 crystallizes in a rhombic structure of the ZnAhS4 type with lattice parameters a = 1.289 nm; b = 0.751; c =
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0.609 nm. According to [32], this compound exists in two crystalline modifications: the low-temperature compound has a trigonal one (Sp.gr. P3ml, a = 0.3654 (2) nm; c = 1.20556 nm), and the high-temperature - rhombic (a = 1.289; b = 0.751; c = 0.609 nm) structure.
The FeGaInS4 compound also melts congruently (1375 K) and has a trigonal structure of the ZnAhS4 type (Sp.gr.P-3m1) with parameters: a = 0.37765, c = 1.22257 nm [33, 34].
The boundary quasi-binary components of the FeS-FeGa2S4-FeGaInS4 system were studied in [29, 33]. According to [29], the 2FeS - FeGa2S4 system is eutectic type. The eutectic
had a composition of ~ 53 mol% FeGa2S4 and crystallized at 1328 K. The Fe2Ga2S5 compound is formed by a solid-phase reaction at 1043 K. According to [33], the 2FeS - FeGaInS4 system also has a eutectic type phase diagram. The eutectic coordinates are 63 mol% FeGaInS4 and 1310 K. The FeGa2S4-FeGaInS4 system is characterized by the formation of a continuous series of solid solutions between FeGaInS4 and the low-temperature modification of FeGa2S4 [33]. It is assumed that the formation of solid solutions leads to a sharp increase in the temperature of the polymorphic transition FeGa2S4 (1327 K) and the establishment of peritectic equilibrium at ~ 1410 K.
Experimental part
2.1. Materials and synthesis
The initial compounds FeS, FeGa2S4 and FeGaInS4 were synthesized using high-purity iron (99.995%), indium (99.999%), gallium (99.999%) and sulfur (99.99%) purchased from Alfa Aesar.
Stoichiometric mixtures of elements were placed in a quartz ampoule which was evacuated to a residual pressure of ~ 10-2 Pa. The syntheses were carried out in a two-zone furnace. In the case of FeS, the lower "hot" zone was slowly heated from a room temperature to a temperature of 1400 K, and for FeGa2S4 and FeGaInS4 compounds it was 30-50 K above their melting points, and part of the ampoule outside the furnace was cooled with water ("cold" zone). The interaction of the components occurrs in the "hot" zone, and in the "cold" zone, the chalcogen condenses and returns to the interaction zone. As a result of the reaction in the "cold" zone, the mass of chalcogen gradually decreased and within 1-2 hours it is consumed almost completely. After that, the ampoule was completely placed in the oven and kept at the indicated temperature for 2-3 hours. The obtained samples were subjected to heat treatment at 800 K for 100 hours in order to increase the crystallinity of the synthesized compounds.
The alloys of the studied system were prepared through melting pre-synthesized compounds in evacuated quartz ampoules. The
alloys were first annealed at 1000 K (100 h), then at 900 K (300 h) and cooled in a switched off the furnace. Some alloys, after heat treatment at 1200 K or 900 K, were quenched in cold water.
2.2. Methods
The differential thermal analysis (DTA) and X-ray powder diffraction technique (XRD) were used for the analysis of samples. DTA was carried out using the NETZSCH 404 F1 Pegasus system from room temperature to ~ 1450 K, depending on the composition of the alloys at a heating rate of 10 K-min-1. Thermal effects temperatures were determined mainly from heating curves. The temperature accuracy was ± 2 K.
Powder X-ray diffraction patterns were recorded on a Bruker D2 Phaser diffractometer using Cu Ka1 radiation at room temperature.
According to DTA, the synthesized compounds melt at 1460 K (FeS), 1420 K (FeGa2S4) and 1375 K (FeGaInS4). Our data are consistent with published data [25, 29, 33]
X-ray diffraction patterns of the synthesized compounds also showed the formation of single-phase materials. The calculated lattice parameters of hexagonal FeS (a = 0.34440 nm, c = 0.57260 nm), trigonal FeGa2S4 (a = 0.36543; c = 1.20558 nm) and FeGaInS4 (a = 0.37765, c = 1.22257 nm) are good consistent with published data [28, 30, 34].
Results
Combined analysis of the obtained experimental data allowed us to obtain a general scheme of the phase equilibria, including isothermal sections at 1200 K and 900 K, polythermal sections 2FeS- [A], FeGa2S4- [B] ([A] and [B] alloys with "FeGa1.5In0.5S4" and "Fei,5 Ga0.5In0.5S3" compositions, respectively) of the phase diagram as well as the projection of the liquidus surface (Figs. 1-4).
According to the data obtained, the FeS-FeGa2S4-FeGaInS4 system referrs to quasi-
ternary systems with monovariant eutectic and peritectoid equilibria.
Isothermal sections at 1200 K and 900
K. Continuous solid solutions along the boundary system FeGa2S4-FeGaInS4 (P-phase) are in connod tie with solid (a) solutions based on the high-temperature modification of FeS and form a two-phase region a+P, which at 1200 K covers the entire area of the concentration triangle (Fig. 1a).
a - " 6
Fig.1. Isothermal sections of the FeS-FeGa2S4-FeGaInS4 system at 1200 K (a) and 900 K(b).
Below 900 K, in the FeS-FeGa2S4 boundary system, there is a ternary compound Fe2Ga2S5 formed by the solid-phase reaction between FeS and FeGa2S4. This leads to the formation of Fe2Ga2S5+P and a+P+Fe2Ga2S5 phase regions. The isothermal section at 900 K clearly demonstrates this (Fig. 1b).
Phase fields on both isothermal sections are confirmed by powder XRD analysis. As an example, Fig. 2 presents powder diffraction patterns of two annealed alloys (Fig. 1b, samples # 1 and # 2) with the reflection lines of the phases coexisting in them. As can be seen, alloy # 1 consists of a two-phase mixture of FeS (low-temperature modification) and the P-phase. Sample # 2 is three-phase - FeS +
Fe2Ga2S5+p. A comparison of the reflection angles with the diffraction patterns of alloys of the FeGa2S4- FeGaInS4 side system showed that the P- phase in both samples has a composition of ~50 mol% FeGaInS4, which is in accordance with Fig. 1b.
The liquidus surface (Fig. 3) consists of three areas corresponding to the primary crystallization of the a, P and P'- phases (P' -solid solutions based on the high-temperature modification of FeGa2S4). The last two areas are delimited by us conditionally (P1P2 dashed line). P1P2 curve refers to monovariant peritectic equilibrium
L+P' o p (1)
» FeS i FeiGaiSä
+ ß-
m FeS ♦ ß- (J»a.3a
2-Theta - Scale
Fig. 2. Powder diffraction patterns of alloys # 1 and # 2 showed on Fig.1
The fields of primary crystallization of a-and P- phases are separated by the e1e2 eutectic
curve with the monovariant equilibrium L o a+ß (2)
Fig.3. Liquidus surfaces projection of the FeS- FeGa2S4- FeGaInS4 system
Polythermal section FeGa2S4 - [B] (Fig. phases is accompanied by a sharp increase in 5). The liquidus of this section consists of three the temperature of the polymorphic transition curves, which from left to right correspond to FeGa2S4 (from 1330 K to ~ 1410 K) and the
the primary crystallization of P'-, P- and a- establishment of peritectoid equilibrium (1). solid solutions. The formation of P'-and P-
Fig. 4. Polythermal section 2FeS- [A] of the FeS- FeGa2S4- FeGaInS4 system
Polythermal section FeGa2S4- [B] (Fig. 5). The liquidus of this section consists of three curves, which from left to right correspond to the primary crystallization of P'-, P- and asolid solutions. The formation of P'-and P-
phases is accompanied by a sharp increase in the temperature of the polymorphic transition FeGa2S4 (from 1330 K to ~ 1410 K) and the establishment of peritectoid equilibrium (1).
Fig. 4. Polythermal section FeGa2S4- [B] of the FeS- FeGa2S4- FeGaInS4 system
The intersection point of liquidus curves of a and P- phases corresponds to the beginning of a monovariant eutectic reaction (2). During this reaction, a three-phase region L+a+P is formed, and upon its completion, a two-phase region a+P is formed.
According to our data (Figs. 1, 4, 5), the homogeneity regions of the a and P- phases of the above sections are maximum at the eutectic temperature (1310-1330 K) and amount to 6-7 mol%.
Conclusion
Based on the experimental data, we obtained a general scheme of phase equilibria in the FeS-FeGa2S4-FeGaInS4 system, including the projection of the liquidus surface, two polythermal sections, and isothermal sections of the phase diagram at 1200 and 900 K. At 1200 K, the system is characterized by the presence of a continuous series of solid solutions along the side system
FeGa2S4-FeGaInS4 (P-phase) and a-solid solutions based on the high-temperature modification of FeS, which form a wide two-phase region a + p. At 900 K, the Fe2Ga2S5 compound is involved in phase equilibria, which leads to the formation of heterogeneous regions Fe2Ga2S5+P u FeS+Fe2Ga2S5+p. The results can be used to develop new magnetic materials based on P-solid solutions.
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FeS- FeGaS- FeGaInS4 SiSTEMi
F.M. M9mmzdov
AMEA Kataliz vd Qeyri-üzvi Kimya institutu Baki çdhdri, H.Cavidpr.113, AZ-1143 e-mail: faikmamadov@mail.ru
Differensial termiki vd rentgenfaza analiz metodlari ild FeS-FeGa2S4-FeGaInS4 sistemindd faza tarazligi tddqiq edilmiçdir. Sistemin likvidus sdthinin proeksiyasi, 1200 vd 900 K temperaturlarda izotermik kdsikldrin faza diaqramlari qurulmuçdur. Müdyydn edilmiçdir ki, sistem monovariant evtektik vd peritektoid tarazligi olan hvazi^lü sistemd aiddir. Sistem 1200 K-dd FeGa2S4-FeGaInS4
(ß- faza) yan kasiyi boyunca fasilasiz bark mahlullarin mövcudlugu vd FeS (a-) yüksak temperaturlu modifikasiyasi asasinda hallolma sahasinin olmasi ila xarakteriza olunur. Üglü sistemin FeS-FeGa2S4 yan kasiyinda 900 K temperaturda Fe2Ga2Ss üglü birla§masi amala galir. Bu birla§ma Fe2Ga2Ss + ß va Fe2Ga2Ss + a + ß heterogen sahalari amala gatirir ki, bunun da tasirindan a + ß iki fazali saha ahamiyyatli daracada kigilir. Agar sozlw. FeGa2S4, FeS, FeGaInS4, faza diaqrami, likvidus, bark mahlullar.
СИСТЕМА FeS- FeGa2S4- FeGaInS4 Ф.М. Мамедов
Институт катализа и неорганической химии Национальной АН Азербайджана, пр. Г. Джавида, 113, AZ-1143, Баку, Азербайджан e-mail: _ faikmamadov@mail.rH
Методами дифференциально-термического и рентгенофазового анализов исследованы фазовые равновесия в системе FeS-FeGa2S4-FeGaInS4. Построены проекция поверхности ликвидуса и изотермические сечения фазовой диаграммы при 1200 и 900 К. Установлено, что она относится к квазитройным системам с моновариантными эвтектическим и перитектоидным равновесиями. При 1200 К система характеризуется наличием непрерывного ряда твердых растворов вдоль боковой системы FeGa2S4-FeGaInS4 (ß-фаза) и твердых растворов на основе высокотемпературной модификации FeS (a-), которые образуют широкую двухфазную область a+ß. При 900 К в боковой системе FeS-FeGa2S4 образуется тройное соединение Fe2Ga2Ss, которое формируя гетерогенные области Fe2Ga2S5+ ß и Fe2Ga2Ss+ a+ß ниже этой температуры значительно сужает двухфазную область a+ ß.
Ключевые слова: FeGa2S4, FeS, FeGaInS4, фазовая диаграмма, ликвидус, твердые растворы.
