PHYSICO-CHEMICAL İNVESTİGATİON OF PHASE EQUILIBRIUM AND GLASS FORMATION IN THE AsS-Cu2Cr4Te7 SYSTEM

Norwegian Journal of development of the International Science No 165/2025 7 CHEMICAL SCIENCES PHYSICO-CHEMICAL İNVESTİGATİON OF PHASE EQUILIBRIUM AND GLASS FORMATION IN THE AsS-Cu2Cr4Te7 SYSTEM Ismailova S. Postgraduate research fellow Aliyev I. Doctor of Chemistry, prof., head. lab. Institute of Catalysis and Inorganic Chemistry, named after M. Nagiyev, Ministry of Science and Education of the Republic of Azerbaijan. Ismailov T. Candidate of Medical Sciences, associate professor. Azerbaijan State Medical University named after N. Narimanov, Baku. Ahmedova C. Doctor of Chemistry, prof., Adiyaman University, Faculty of Arts and Sciences, Department of Chemistry, Turkiye https://doi.org/10.5281/zenodo.17226043 Abstract Phase formation and vitrification in the AsS-Cu2Cr4Te7 system are studied by the methods of physical and chemical analysis: differential thermal (DTA), X-ray diffraction (XRD), microstructural (MKA), and also determination of microhardness and density. The T-x phase diagram is constructed. It is established that the AsSCu2Cr4Te7 system is a partially quasibinary section. Based on the results of the microstructural analysis, it was established that in the AsS-Cu2Cr4Te7 system at room temperature, the solubility of 12 mol.% AsS based on the Cu2Cr4Te7 compound was found, while the area of the solid solution based on the AsS compound is practically undefined. During slow cooling in the AsS-Cu2Cr4Te7 system, a region of glass formed on the basis of AsS 10 mol. % Cu2Cr4Te7. The area of AsS-based glass when cooled in ice water is 15 mol.% Cu2Cr4Te7. In the interval of concentrations of 10–30 mol. % Cu2Cr4Te7 there are alloys of glass crystal composition. Keywords: peritectic, quasibinary, glass, solid solution, microhardness. Introduction Arsenic chalcogenides, one of the main elements of Group V, are known to form in a glassy state. Recently, arsenic chalcogenides, as well as complex glassy alloys and compounds based on them, have attracted the attention of researchers due to their unique functional properties. Arsenic chalcogenides, as well as complex glassy alloys and compounds based on them, are widely used in various fields of photoelectronics as photosensitive, luminescent, and acousto-optic materials [1–8]. Chromium chalcogenides form magnetic materials with a number of chalcogenides, including copper chalcogenides [9–15]. We have studied a number of systems involving the compound Cu2Cr4Te7 [16, 17]. The physical properties of arsenic monosulfide AsS remain virtually unexplored. Therefore, it can be expected that new complex phases and glassy alloys obtained by the chemical interaction of AsS and Cu2Cr4Te7 chalcogenides can also be semiconductor materials with magnetic and magneto-optical properties. The aim of this work is to conduct a physicochemical study of the phase equilibrium in the AsSCu2Cr4Te7 system, construct its phase diagram, and determine the glass transition and solid solution boundaries. The glassy compound AsS melts at 318°C with an open maximum and crystallizes in the orthorhombic syngony, with lattice parameters: a = 9.32; b = 13.546; c = 6.585 Ǻ [18]. The compound Cu2Cr4Te7 melts incongruently at 1000°C and has a wide homogeneity region [15]. Experimental Section The synthesis of AsS-Cu2Cr4Te7 alloys was carried out in two stages. In the first stage, AsS and Cu2Cr4Te7 compounds were synthesized using the ampoule method. The AsS compound was obtained from the elements in a single-zone furnace at a temperature of 400-700°C. The AsS compound was obtained as a glass with normal cooling. A two-zone furnace was used to obtain the Cu2Cr4Te7 compound from the elements. To synthesize the Cu2Cr4Te7 compound of the AsS-Cu2Cr4Te7 system, elements taken in stoichiometric composition are placed in a 20-cm-long ampoule. To synthesize the Cu2Cr4Te7 compound, part of the ampoule is inserted into a furnace at 1100°C. The remaining portion of the ampoule is left outside the furnace. During this process, Te vapor initially begins to form. This process continues until the Te vapor disappears. After maintaining the reaction at 1100°C for 3 hours, the furnace temperature is increased to 950°C, held for 4 hours, and then cooled by disconnecting it from the power source. In the second stage, the AsSCu2Cr4Te7 alloys were synthesized from the AsS and Cu2Cr4Te7 compounds using the ampoule method. The alloys of the system are then analyzed using physicochemical methods. Differential-thermal analysis was performed on a Thermoscan-2 pyrometer. Chromel-alumel was used as a thermocouple, and the heating rate was 5°C/min. Norwegian Journal of development of the International Science No 165/2025 8 Microstructural analysis was performed on an MIM-8 microscope. HNO3 + HF solutions (1:2) were used as etchants to reveal phase boundaries in the samples. X-ray phase analysis of the alloys was performed on a D2 PHASER X-ray diffractometer. CuKα radiation and a Ni filter were used as the anode. Microhardness was measured on a PMT-3 metallographic microscope. Density was determined pycnometrically, using toluene as the filler solution. Results and Discussion Alloys of the AsS-Cu2Cr4Te7 system are compact, and their color ranges from red to black. The alloys of the system are resistant to air, water, and organic solvents. They are highly soluble in strong acids (HNO3, H2SO4). Alloys rich in AsS are soluble in alkalis (NaOH, KOH). It should be noted that the physicochemical analyses of the alloys were carried out in both the crystalline and glassy states. Thermal analysis of the alloys before heat treatment revealed that thermal effects were observed in the thermograms of samples in the range of 0–15 mol. % Cu2Cr4Te7 at a temperature of 170°C, which corresponds to the softening temperature of glass. The composition of the alloys of the system was studied by microstructural analysis, and it was found that there is a wide range of solubility in the region of the Cu2Cr4Te7 compound. The microstructures of the alloys in the range of 0–15 mol. % Cu2Cr4Te7 appear as opaque single-phase. Microstructural analysis revealed that only single-phase alloys were obtained based on the Cu2Cr4Te7 compound. Figure 1 shows the microstructure of alloys with concentrations of 40, 70, and 90 mol. % Cu2Cr4Te7. As can be seen from the figure, alloys with concentrations of 40 and 70 mol. % Cu2Cr4Te7 are two-phase. The alloy with a concentration of 90 mol. % Cu2Cr4Te7 is single-phase and represents a solid solution based on the Cu2Cr4Te7 compound. Fig. 1. Microstructure of AsS-Cu2Cr4Te7 alloys. 1–40 mol. %, 2–70 mol. %, 4–90 mol. % Cu2Cr4Te7. Fig. 2. X-ray diffraction patterns of AsS-Cu2Cr4Te7 alloys. 1-5, 2-10, 3-30, 4-50, 5-90, 6-100 mol. % Cu2Cr4Te7. To clarify the results of differential thermal and microstructural analyses of AsS-Cu2Cr4Te7 alloys, Xray diffraction analysis was performed on alloys with contents of 5, 10, 30, 50, and 90 mol. % Cu2Cr4Te7 (Fig. 2). Diffraction maxima in the diffraction patterns of alloys in the range of 0–30 mol.% Cu2Cr4Te7 in the studied system revealed weak lines. 1 2 3 Norwegian Journal of development of the International Science No 165/2025 9 Fig.3. T-x phase diagram of the AsS-Cu2Cr4Te7 system. 1during slow cooling, 2during cooling in ice water, glass area Table 1. Physico-chemical properties of glassy alloys of the AsS-Cu2Cr4Te7 system (glass region) Composition, mol. % Thermal effects, oC Microhardness, MPа Density, q/cm3 MSA AsS Cu2Cr4Te7 Tg Тcrus. Тmelt. 100 0 170 220 318 1350 3,35 Şüşə 97 3 170 220 315 1380 3,55 — 95 5 175 230 315 1380 3,60 — 93 7 180 235 320 1380 3,67 — 90 10 190 240 270 1385 3,72 — 85 15 190 245 400 1390 3,90 Glass-crust 80 20 190 250 510 1400 4,10 Glass-crust 70 30 190 265 380 1430 4,47 Glass-crust 60 40 190 270 450 1440 4,85 crustal This indicates the glassy nature of the samples in this region. Diffraction maxima were observed in the X-ray diffraction patterns of alloys containing 50 and 90 mol.% Cu2Cr4Te7. Analysis revealed that the diffraction lines in the diffraction pattern of the sample containing 90 mol. % Cu2Cr4Te7 are identical to those of the Cu2Cr4Te7 compound, indicating that this sample is a solid solution alloy based on Cu2Cr4Te7. Based on the results of a comprehensive physicochemical analysis, a phase diagram of the AsSCu2Cr4Te7 system was constructed (Fig. 3). In the AsSCu2Cr4Te7 system, glassy AsS-based alloys with a composition of 10 mol. % Cu2Cr4Te7 formed upon slow cooling. Alloys with a glassy-crystalline composition are present in the layer range of 10–30 mol. % Cu2Cr4Te7. Table 1 shows the compositional dependences of the softening and crystallization temperatures, microhardness, and density of alloys from the glassy and glassy-crystalline regions. Table 2 presents some physicochemical properties of the alloys in the crystalline state of the system. AsS 20 40 60 80 Cu2Cr4Te7 mol. % L L+AsS L+Cr2Te3 L+Cr2Te3+ β α L+ β AsS+ α 200 400 600 800 1000 1200 t,oC 1000o 1210o 270о 1 2 Glass 318о L+AsS+ Cr2Te3 Norwegian Journal of development of the International Science No 165/2025 10 Table 2. Composition, results of differential thermal analysis, determination of microhardness and density of AsSCu2Cr4Te7 system alloys in crystalline form Composition, mol. % Thermal effects, oC Density, q/cm3 Microhardness, MPа AsS α AsS Cu2Cr4Te7 0,15 H 0,20 H 100 0,0 318 3,52 660 - 95 5,0 270,315 3,60 700 - 90 10 270 3,75 720 - 85 15 270,400 4,05 740 - 80 20 270,510 4,24 - - 70 30 270,380,650 4,59 - - 60 40 270,450,780 4,95 - 2000 50 50 270,600,890 5,33 - 2000 40 60 270,720,975 5,67 - 2000 30 70 270, 810,1050 6,03 - 2000 20 80 270,900,1120 6,38 - 2000 10 90 545,960,1175 6,74 - 2000 5,0 95 800,980 7,22 - 2000 0,0 100 1000,1210 7,10 - 1970 The liquidus of the AsS-Cu2Cr4Te7 system represents the initial crystallization curves of the β-solid solution obtained from Cu2Cr4Te7. In the system, primary crystals of the AsS compound precipitate in the range of 0–20 mol. % Cu2Cr4Te7. The system undergoes a process of eutectic equilibrium and peritectic transformation. The decomposition of the Cu2Cr4Te7 compound results in the formation of three-phase alloys consisting of (L + AsS + Cr2Te3) and (L + Cr2Te3 + β). Since the peritectic process L + Cr2Te3 ↔ Cu2Cr4Te7 occurs, two-phase alloys consisting of AsS + α crystallize below the solidus line in the system. The microhardness and density of AsS-Cu2Cr4Te7 alloys were studied as a function of their composition in the glassy and crystalline states (Tables 1 and 2). Two different microhardness values were determined in the system. Before heat treatment, i.e. in the glassy state, the microhardness and density of glasses obtained on the basis of AsS are Hμ=(1350-1440) MPa, ρ=(3.35-4.85) g/cm3, for α-solid solutions based on the compound Cu2Cr4Te7 the microhardness is Hμ=(27502800) MPa, and the density ρ=3.52-7.22 g/cm3. After heat treatment, the microhardness of samples from the glassy region is Hμ=(660-740) MPa, ρ=(3.53-4.59) g/cm3. The microhardness and density of the crystalline phases do not change. It was found that during the glass-crystal transition the hardness of the alloys decreases and their specific gravity increases. Conclusion Thus, based on the results of comprehensive physicochemical analysis methods, a phase diagram of the AsS-Cu2Cr4Te7 system has been constructed. The phase diagram of the system is partially quasi-binary and belongs to the eutectic type. The system undergoes eutectic equilibrium and peritectic transformation, leading to the crystallization of two-phase alloys of the AsS + α composition below the solidus line. In the AsS-Cu2Cr4Te7 system, the AsS-based solid solution region is virtually undefined. The Cu2Cr4Te7based solid solution region is 15 mol. % AsS. The glass transition region of the AsS-based system under normal conditions is determined to be 10 mol. % Cu2Cr4Te7. After cooling in ice water, the glass transition region of the AsS-based system is 15 mol. % Cu2Cr4Te7. 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