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ISSN 2522-1841 (Online) AZ9RBAYCAN KIMYA JURNALI № 4 2018 29
ISSN 0005-2531 (Print)
UDC 541.123/123.8/9:546.568186/23
POLYTHERMAL SECTION SnSe-CuSbSe2 OF PHASE DIAGRAM OF THE Cu2Se-SnSe-Sb2Se3 SYSTEM
E.N.Ismayilova, G.M.Shukurova*, E.R.Aliyeva**, L.F.Mashadieva
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
*Baku State University **Institute of Physics ANAS
Received 04.04.2018
Phase equilibria in the Cu2Se-SnSe-Sb2Se3 system were studied along the SnSe-CuSbSe2 section by means of differential-thermal analysis and X-ray diffraction technique and its phase diagram was constructed. It was found that the SnSe-CuSbSe2 section is quasibinary and refers to an eutectic type with limited solid solutions based on the starting compounds. The solubility based on SnSe and CuSbSe2 is maximal at the eutectic temperature (700 K) and reaches 25 and 5 mol%, respectively.
Keywords: Cu2Se-SnSe-Sb2Se3 system, SnSe-CuSbSe2 section, phase diagram.
Introduction
Complex copper chalcogenides have attracted much attention thanks to their outstanding photoelectric, thermoelectric, non-linear optic and etc. properties [1-3]. On the other hand, these materials exhibit excellent mixed ionic conductivity with Cu+ ions which make them prospective candidates for elaborate ion-selective electrodes or solid-state electrolytes for different kind of electric batteries, sensors, displays, etc. [4, 5]. In particular, the Cu-Sb-Sn-X (X=S, Se) systems are of great interest for the development of new ecologically safe thermoelectric materials [6-8].
Taking this into account, we undertook a complex study of these systems on concentration planes Cu2X-SnX-Sb2X3. This work presents the results of the study of the polythermal section SnSe-CuSbSe2 of the quaternary Cu-Sb-Sn-Se system.
Tin monoselenide SnSe melts congru-ently at 1134 K [9] and crystallizes in the ortho-rhombic system, space group Pcmn, with following lattice parameters: a = 4.46, b = 4.19, c = 11.57; Z = 4 [10].
The CuSbSe2 compound melts congru-ently at 750 K [11]. This compound has the diamond-like structure with Cu atoms occupied in the center of Se-formed tetrahedrons and crystallizes in the orthorhombic system, with space
group Pnma and lattice parameters at room temperature: a = 6.467, b = 4.045 and c = 15.048 A; Z = 4 [12]. Recent studies have shown that ternary selenostibite CuSbSe2 has the better photo-electrical conversion performance and appears to be a promising absorber material for thin-film solar cells due to its attractive optical and electrical properties, as well as earth-abundant, low-cost, and low-toxic constituent elements [13-15], as well as the compound SnSe exhibits exceptionally good thermoelectric properties at high temperatures above ~800 K, including a very low thermal conductivity [16, 17].
Experimental part
Materials and syntheses
The initial compounds SnSe and CuSbSe2 were synthesized by melting of elementary components of high purity (99.999 %) in vacuumed (~10-2Pa) quartz ampoules. The synthesis was carried out at temperatures 500C higher than the melting points of the synthesized compounds. Further ampoules with tin selenide and ternary selenostibite were slowly cooled to room temperature. Differential thermal analysis and powder X-ray diffraction technique were employed to probe the phase-purity of the synthesized starting compounds SnSe and CuSbSe2.
A series of SnSe-CuSbSe2 alloys with compositions of 10, 20, 30, 40, 50, 60, 70, 80 and 90 mol% CuSbSe2 was prepared for the investigation. Alloys were prepared from pre-synthesized starting compounds by melting in a vacuum.
In order to achieve the equilibrium state in alloys, cast non-homogenized samples obtained by slow cooling of melts were ground into a powder, thoroughly mixed and pressed into tablets with a mass of 0.8-1g, and then annealed at 675 K for 500 hours.
Methods
Studies of samples carried out by differential-thermal analysis (DTA) and powder X-ray diffraction (XRD) method.
The differential-thermal analysis was carried out in the temperature range from room temperature to 1200 K with a heating rate of 10 K/min on a differential scanning calorimeter (NETZSCH 404 F1 Pegasus system). The measurement results were processed using the NETZSCH Proteus Software. The accuracy of the temperature measurement was within ±2 K.
X-ray phase analysis was carried out at room temperature on a Bruker D8 ADVANCE diffractometer with CuX^ -radiation. The X-ray images were indexed using Topas V3.0 software Bruker.
Results and discussion
The phase diagram of the SnSe-CuSbSe2 system was constructed based on DTA and XRD data (Table, Figure 1).
Results of DTA for SnSe-CuSbSe2 alloys
Composition, mol % CuSbSe2 Thermal effects, K
0 (SnSe) 1153
10 970, 1070
20 800, 1000
30 700, 720, 950
40 700, 720, 900
50 700, 720, 890
60 700
70 700, 730
80 700, 740
90 700, 750
100 (CuSbSe2) 760
Fig. 1. Phase diagram of the SnSe-CuSbSe2 system.
It was found that the SnSe-CuSbSe2 section is quasibinary and refers to a eutectic type with limited solid solutions based on the starting compounds. The solubility based on SnSe and CuSbSe2 at the room temperature reaches ~22 and 3 mol%, respectively. Liquidus of this system consists of two branches, which characterize primary crystallization of the solid solutions based on SnSe (P-phase) and CuSbSe2 (y-phase). The eutectic has a composition of 65 mol% CuSbSe2 and crystallizes at 700 K. An extension of the P-phase (25 mol %) and y-phase (5 mol%) is maximal at the eutectic temperature. The nature of the thermal effects at 720 K for alloys with a composition of 30-50 mol% CuSbSe2 was not established. It can be assumed that these thermal effects relate to the peritectic reaction of formation of an intermediate compound with a very narrow temperature range of existence (700-720 K).
The XRD data confirm the plotted phase diagram. As can be seen from Figure 2, the XRD data of the SnSe-CuSbSe2 alloys 3-6 confirms their biphasic composition. The XRD patterns of these alloys consist of a set of reflection lines of the P-phase (SnSe) and y-phase (CuSbSe2). The XRD patterns of the alloy 2 is similar to SnSe.
E.N.ISMAYILOVA et al. 31
Intensity (cps)
6.0e+004
Fig. 2. XRD patterns for some alloys of the SnSe-CuSbSe2 system at room temperature: 1 -SnSe, 2 - 20 mol% CuSbSe2, 3 - 30 mol% CuSbSe2, 4 - 50 mol% CuSbSe2, 5 - 60 mol% CuSbSe2, 6 - 80 mol% CuSbSe2, 7 - CuSbSe2.
References
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Cu2Se-SnSe-Sb2Se3 SISTEMININ FAZA DIAQRAMININ SnSe-CuSbSe2 POLITERMIK KЭSIYI
E.N.ismayllova, G.M §йкйгоуа, Е^ЭИуеуа, L.F.Mэ§эdiyeva
Cu2Se-SnSe-Sb2Se3 ид1и sistemi differensial termiki vэ rentgen faza analizi metodlaп ilэ SnSe-CuSbSe2 kэsiyi uzrэ tэdqiq edilmi§ vэ kэsiyin faza diaqraml qurulmu§dur. МИЭУУЭП ейПт^йи- ki, SnSe-CuSbSe2 kэsiyi kvazibinar olmaqla evtektik tipэ aiddir. Sistemdэ komponentlэr эsaslnda mэhdud bэrk шаИМ sahэlэri mбvcuddur. SnSe vэ CuSbSe2 эsaslnda hэUolma evtektik temperaturda (700 К) maksimaldlr vэ muvafiq olaraq 25 vэ 5 то1% ^^п gэlir.
Адаг sдzlэr: Си28е-8п8е-8Ь28ез 8п8е-Сы8Ь8е2 кэ^чуг, faza diaqraml.
ПОЛИТЕРМИЧЕСКИЙ РАЗРЕЗ SnSe-CuSbSe2 ФАЗОВОЙ ДИАГРАММЫ СИСТЕМЫ
Cu2Se-SnSe-Sb2Seз
Э.Н.Исмайлова, Г.М.Шукюрова, Э.Р.Алиева, Л.Ф.Машадиева
Фазовые равновесия в системе изучены вдоль разреза SnSe-CuSbSe2 методами дифферен-
циально-термического и рентгенфазового анализов. Построена фазовая диаграмма разреза SnSe-CuSbSe2 и установлено, что это сечение является квазибинарным и относится к эвтектическому типу с ограниченными твердыми растворами на основе исходных соединений. Растворимость на основе SnSe и CuSbSe2 является максимальной при эвтектической температуре (700 К) и достигает 25 и 5 мол%, соответственно.
Ключевые слова: система Си^е-БпБе-БЬ^ез, разрез SnSe-CuSЬSe2, фазовая диаграмма.
