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ISSN 2522-1841 (Online) AZERBAIJAN CHEMICAL JOURNAL № 2 2021 37
ISSN 0005-2531 (Print)
UDC 546 (711.682.24)
REFINEMENT OF THE PHASE DIAGRAM OF THE MnTe-In2Te3 SYSTEM
F.M.Mammadov
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
Received 11.12.2020 Accepted 15.03.2021
The MnTe-In2Te3 system was re-investigated by DTA and XRD methods, and its phase diagram was constructed somewhat differently from the previously known ones. It was found that the system is characterized by the formation of the Mn!n2Te4 compound congruently melting at 1025 K with a wide (4967 mol% In2Te3) homogeneity region. This phase is in eutectic equilibrium (1015 K) with solid solutions based on lt-MnTe (lt - low temperature) and in peritectic equilibrium with solid solutions based on In2Te3. A comparative analysis of the results obtained with the literature data is carried out.
Keywords: MnTe-In2Te3 system, phase diagram, manganese and indium tellurides, solid solutions.
doi.org/10.32737/0005-2531-2021-2-37-41 Introduction
Ternary and more complex chalcogenides based on 3d-elements, in particular manganese, are of great practical interest as materials combining magnetic and semiconducting properties [1-8]. Recent studies have shown that some of them are magnetic topological insulators and extremely promising for use in spintronics and quantum computing [9-15].
The development and creation of new methods for directed synthesis of complex phases and materials require the study of phase equilibria in the corresponding systems [16-19].
With purpose of search and development a physicochemical basis for the creation of new magnetic semiconductors, we have undertaken a study of phase equilibria in MX- Ga2X3-M2X3 (M - Mn, Fe; X - S, Se, Te) systems. The results obtained for some systems of this type [20-25] displayed the formation of wide areas of solid solutions along the MGa2X4-MIn2X4 sections. At the same time, an analysis of the literature data has revealed that the phase diagrams of some boundary quasi-binary components of the indicated quasi-ternary systems require clarifying. In papers [26, 27] we presented refined T-x diagrams of some similar systems.
Our preliminary experimental results obtained under the study of the MnTe-Ga2Te3-In2Te3 system found out their inconsistency with the known [28] phase diagram of the MnTe-
In2Te3 boundary system. Taking into account it the purpose of our work was to re-study phase equilibria in the MnTe-In2Te3 system.
The initial compounds of the investigated system have been studied in detail. The MnTe compound melts with decomposition by a peritectic reaction at 1425 K and undergoes polymorphic transitions at 1270 and 1305 K [29]. At the low-temperature modification MnTe (lt-MnTe) crystallizes in a hexagonal structure (Sp.Gr. P63/mmc) with lattice parameters a = 0.41498 nm, c = 0.67176 nm [12].
The In2Te3 compound melts congruently (940 K) [29] and crystallizes in a cubic structure (Sp.Gr.F43m) with lattice parameters a = 0.616 nm or 1.850 nm [30].
Experimental part
Materials and synthesis
MnTe and In2Te3 compounds were synthesized using high-purity manganese (Mn -99.99%), indium (In - 99.999%), tellurium in granules (Te - 99.999%) purchased from Alfa Aesar. During the synthesis of In2Te3 stoichio-metric amounts of elements were placed in an evacuated ~10-2 Pa quartz ampoule and melted in a single-zone furnace at 990 K. MnTe synthesis was also carried out under vacuum conditions in a glass-graphite crucible, placed in a quartz ampoule, at 1450 K.
The individuality of both synthesized compounds was controlled by DTA and XRD. The
obtained melting points and crystal lattice parameters coincided within the error limits (±2 K and ±0.0003 A) with the above literature data.
The alloys of the studied system were prepared by melting the initial compounds in various ratios in evacuated quartz ampoules, followed by homogenizing annealing at 850 K for ~500 h.
Research methods
Differential thermal analysis (DTA) was carried out on a Netzsch 404 f1 Pegasus System (chromel-alumel thermocouples) in the temperature range from room temperature to ~1450 K at a heating rate of 10 K/min. Phase and structural studies were carried out based on powder diffraction data obtained on a D2 Phaser diffractometer using the Eva and Topas 4.2 software (Bruker, Germany; CuK „-radiation, interval of angles 5 < 29 < 800, recording rate 0.030/0.2 min).
Results and discussion
The analysis of powder diffraction patterns showed that alloys with compositions 5067 mol% In2Te3 have a new diffraction pattern differed from the initial compounds. Figure 1
presents as an example the diffraction patterns of alloys with compositions of 50 and 65 mol% In2Te3. It is also seen from this Figure 1 that the diffractogram of the 80 mol% In2Te3 alloy is qualitatively are identical to the diffraction pattern of pure In2Te3 with some shift in the reflection angles. Also, according to the XRD data (Figure 1), the diffraction pattern of an alloy containing 30 mol% In2Te3 includes accumulation of reflection lines of phases based on MnTe and MnIn2Te4, and an alloy with a composition of 70 mol% In2Te3 consists of reflection lines of phases based on In2Te3 and MnIn2Te4.
The phase diagram of the MnTe- In2Te3 system was constructed using the joint processing of data obtained by methods DTA and RFA (Figure 2). As can be seen, the system is non-quasi-binary due to the incongruent character melting of MnTe, but it is stable below the peritectic temperature (1425 K). The liquidus consists of 5 curves responcible for the primary crystallization of Mn, a'- and a-solid solutions based on two modifications of MnTe, y-phase based on MnIn2Te4 and P-phase based on In2Te3 (Figure 2).
Fig.1. Powder diffraction patterns of some alloys of the MnTe-In2Te3 system.
Fig.2. Phase diagram of the MnTe-In2Te3 system.
The MnIn2Te4 compound melts congru-ently at 1025 K and has a wide (□49-67 mol% In2Te3) homogeneity region (y-phase).
The intermediate y-phase forms a eutectic with the a-phase (e). Eutectic has coordinates: 45 mol.% In2Te3 and 1015 K. The system has a peritectic equilibrium L+y o- P at 970 K. The peritectic point (P) has a composition of 83 mol% In2Te3. The horizontal lines at 1420 and 1295 K correspond to peritectic (L+Mn o- a') and metatectic (a' o- L+ a) equilibria.
The T-x diagram we constructed differs significantly from the one given in [28]. Thus, according to [28], the MnIn2Te4 (D) compound melts at ~1040 K and has a constant composition. Moreover, according to [28], MnIn2Te4 forms a eutectic with In2Te3 at 878 K, which was not confirmed by us. We also obtained data on phase transitions based on MnTe that differ from those given in [28].
Conclusion
In this work, we presented a new scheme of phase equilibria in the MnTe-In2Te3 system, which differs from the one presented in the literature. In contrast to literature data, we showed that this system is non-quasi-binary due to the
incongruent melting of MnTe. We have found that the ternary compound MnIn2Te4 has a wide homogeneity region and is in peritectic equilibrium with solid solutions based on In2Te3, that it is also differed from data [28].
The new phases of the variable composition obtained in this work are of interest as potential magnetic materials.
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MnTe-In2Te3 SÍSTEMÍNÍN FAZA DÍAQRAMININ DOQÍQLa§DÍRÍLMOSÍ
F.M.Mammadov
MnTe-In2Te3 sistemi DTA va XRD metodlan ila yenidan tadqiq edilmi§ уэ avvallar adabiyyatda gostarilandan bir qadar farqlanan faz diaqrami qurulmu§dur. Sistemda geni§ (49-67 mol.% In2Te3) homogenlik sahasi ila xarakteriza olunan va 1025 K-da konqruyent ariyan MnIn2Te4 birla§masinin amala galmasi a§kar edilmi§dir. Bu faza lt MnTe asasindaki bark mahlulla evtektik (1015 K), In2Te3 asasindaki bark mahlulla isa peritektik tarazliqdadir. Olda olunan naticalarin adabiyyat malumatlari ila müqayisali tahlili apanlmi§dir.
Agar sozlar: MnTe-In2Te3 sistemi, faz diaqrami, manqan va indium telluridlari, bark mahlullar.
УТОЧНЕНИЕ ФАЗОВОЙ ДИАГРАММЫ СИСТЕМЫ MnTe-In2Te3
Ф.М.Мамедов
Система MnTe-In2Te3 повторно исследована методами ДТА и XRD, и построена ее фазовая диаграмма, которая несколько отличается от ранее приведенной в литературе. Установлено, что в системе наблюдается образование конгруэнтно плавящегося при 1025 K соединения MnIn2Te4 с широкой (49-67 мол.% In2Te3) областью гомогенности. Эта фаза находится в эвтектическом равновесии (1015 K) с твердыми растворами на основе lt-MnTe и в перитектическом равновесии с твердыми растворами на основе In2Te3. Проведен сравнительный анализ полученных результатов с литературными данными.
Ключевые слова: система MnTe-In2Te3, фазовая диаграмма, теллуриды марганца и индия, твердые растворы.
