Study of Phase Formation In The Cute-As2te3System

It is known that compounds and solid solutions based on arsenic chalcogenides occupy an important place among the materials used in optoelectronics [1-3]. Copper chalcogenides and alloys based on them as thermionic and superionic materials are widely used in radio and electronic engineering [4,5]. Some quasi-binary sections with the participation of arsenic chalcogenides and the Cu-As-Se (Te) ternary system have been investigated in the literature [6,7]. However, there is no data in the literature on interactions in the CuTe-As₂Te₃ system. The aim of this work is to synthesize and study the interaction in the CuTe-As₂Te₃ system, as well as to search for new semiconducting phases and solid solutions. The CuTe compound melts incongruently at 367 °C and crystallizes in a rhombic syngony with unit cell parameters: a= 3.16; b= 4.07; c= 6.92 Å, sp. gr. Pmmm-D¹³_2h [8]. According to [9], the CuTe compound melts incongruently at 400 °C. The As₂Te₃ compound melts with an open maximum at 381 °C and crystallizes in monoclinic syngony with lattice parameters: a= 14.339; b= 4.006; c= 9.873Å, β= 95°, sp.gr. C₂/m, the density is ρ= 6.25g/cm³ [10].

The synthesis of the initial components of the system, which was carried out from the elements Cu-99.97; tellurium Te-99.998, and arsenic 99.99 taken in stoichiometric proportions. Triple alloys of the CuTe-As₂Te₃ system were synthesized in a single-temperature furnace by the ampoule method from the CuTe and As₂Te₃ components. Taking into account the peritectic nature of the formation of the CuTe compound, annealing was performed for 350h at a temperature of ~ 20 °C below the final crystallization temperature.

The study of the CuTe-As₂Te₃ ternary system was carried out by methods of physicochemical analysis: Differential Thermal (DTA), X-ray Phase (XRD), Microstructural (MSA), as well as density determination and microhardness measurement.

The obtained alloys of the CuTe-As₂Te₃ system are compact in gray. The system alloys are resistant to water and organic solvents. They dissolve well in acids HNO₃ and H₂SO₄. Alloys rich in As₂Te₃ also dissolve in alkalis (NaOH, KOH). The DTA of the CuTe-As₂Te₃ system showed that the thermograms of the alloys show two and three endothermic effects related to solidus and liquidus. The results of the microstructural analysis show that all alloys of the CuTe-As₂Te₃ system are two-phase. Only based on As₂Te₃ there is an insignificant range of solid solutions, and based on CuTe, solid solutions are practically not found. This indicates that the CuTe-As₂Te₃ section is quasi-binary, of the eutectic type.

To confirm the results of DTA and MSA analyzes, an X-ray phase analysis of alloys of the system 30, 50, and 70mol % As₂Te₃. It was found that the diffraction patterns of alloys with the marked compositions, in addition to the composition of 50 and 92-100mol % As₂Te₃ other alloys consist of mixed diffraction lines of the initial components. Content 50mol. % corresponds to the formula Сu₃As₄Te₉. The data obtained indicate that the CuTe-As₂Te₃ system contains one and two-phase alloys. The state diagram of the system is quasi-binary, eutectic type, characterized by the presence of one chemical compound of the composition Cu₃As₄Te₉. The Сu₃As₄Te₉ compound melts with an open maximum at 320 °С. Cu₃As₄Te₉ and As₂Te₃ form a eutectic of 45mol % As₂Te₃ and melts at 265 °С. The CuTe compound melts incongruently at 400 °C, above the peritectic temperature it decomposes according to the following reaction: CuTe ↔ L + Cu₄Te₃. In the concentration range, 0-25mol % As₂Te₃ primary crystals of Cu₄Te₃ are precipitated from the liquid. During secondary crystallization, three-phase regions are formed (L + Cu₄Te₃ + Cu₃As₄Te₉).

When measuring the microhardness of the alloys of the system, three different values of microhardness were established. The microhardness value for the CuTe compound varies in the range (400-530) MPa. The microhardness value (1960-1980) MPa corresponds to the microhardness of the Cu₃As₄Te₉ compound. The microhardness values for the α-solid solution based on As₂Te₃ vary from 1650MPa to 1850MPa.

The interactions between CuTe and As₂Te₃ are investigated in a wide concentration range and the T-x phase diagram of the system is constructed. It has been established that the CuTe-As₂Te₃ system belongs to the eutectic type. One chemical compound Cu₃As₄Te₉ is formed in the system. It was found that Cu₃As₄Te₉ compounds melt congruently at 320 °С. In the system at room temperature, solid solutions based on As₂Te₃ reach 8mol % CuTe, while solid solutions based on CuTe have practically not been established. CuTe and As₂Te₃ form a eutectic with coordinates 45mol % As₂Te₃, temperature 265 °С.

1. Goglidze TI, Dementev IV, Ishimov VM, Senokosov EA (2007) Influence of thermal evaporation rate on the main physical properties of glassy (As₂S₃) x (As₂Se₃)1-x alloys. Inorgan Materials 43(1): 90-93.
2. Babaev AA, Muradov R, Sultanov SB, Askhabov AM (2008) Effect of preparation conditions on the optical and photoluminescent properties of glassy As₂S₃. Inorgan Materials 44(11): 1187-1201.
3. Rustamov PG, Safarov MG, Aliev II, Ilyasov TM (1979) AS No 689584 (USSR) Photosensitive material.
4. Berezin VM, Vyatkin GP (2001) Superionic semiconductor chalcogenides. p. 135.
5. Gurevich A, Kharkats I (1992) Superionic conductors. M Science, 288.
6. Blasnik R, Gather B (1971) The system Cu₂Te-As₂Te₃. 26: 1073-1078.
7. Aliyev II, Aliyev OM, Mahammadrahimova RS (2019) Phase formation in the system InAs₂S₃Se-InAs₂Se₃S and properties of obtained phases. Journal AZ Chemistry 2: 50-53.
8. (1979) Physicochemical properties of semiconductor substances. Moscow, Russia, 339.
9. Pashinkin AS, Fedorov VA (2003) Phase equilibria in the Cu-Te system. Inorganic Materials 39(6): 539-554.
10. Khvorestanko AS (1972) Arsenic chalcogenides. p. 92.