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14STUDY OF THE Tm-Sb-Te SYSTEM
Sadigov F.
Doctor of Chemical Sciences, Prof., Department of General and Inorganic Chemistry
Baku State University, Baku, Azerbaijan
Ismailov Z.
Ph.D., Associate Professor, Department of General and Inorganic Chemistry
Baku State University, Baku, Azerbaijan
Mirzoeva R.
Ph.D., Researcher, Department of General and Inorganic Chemistry
Baku State University, Baku, Azerbaijan
Qasanova Z.
Researcher, Department of General and Inorganic Chemistry Baku State University, Baku, Azerbaijan
Mamadova S.
Researcher, Department of General and Inorganic Chemistry Baku State University, Baku, Azerbaijan
ABSTRACT
Phase interaction in the Tm-Sb-Te ternary system is investigated along nine internal joins by the methods of physicochemical analysis. Phase diagrams of joins and the liquidus surface projection for the ternary system are constructed.Thee compouds, namely TmSb4Te7(S0, TmSb2Te4(S2),and TmSbTe3(S3).are found in the sys-tem.The frist congruently and participates in the triangulation of theTm-Sb-Te system.
Keywords: system, phase, diagram, compound.
The investigation of phase interaction in the Tm-Sb-Te system is of interest in connection with the application of rare-earth metals for the commutation of thermal elements based on antimony telluride [1,2]. Phase diagrams of boundary binary systems of the ternary system under investigation are taken from [3-5].
In this work, the ternary Tm-Sb-Te system is investigated over the entire concentration range using the methods of physicochemical analysis.
Starting reactants for the alloy synthesis were thulium Tul-O, antimony Sb-B4, and tellurium Te-A2.
The components were directly alloyed in evacuated silica ampules at 1000-1200K (depending on the composition) with subsequent cooling in a switched-off furnace. In order to equilibrate the alloys, they were subjected to homogenizing anneal in evacuated silica ampules for 500 h at temperatures 50-100 K below the solidus temperature.
The samples were investigated using the methods of physicochemical analysis according to the procedure described earlier [6].
Join Eutectic coordinates Composition Of Sb2Te3-based and TmSb4Te7-based solid so-lutions,mol%
Composi-Tion,mol% T,K
Sb2Te- Tm3Te4 85 Sb2Te3 800 3 Tm3Te4
TmSb-TmTe 50 TmSb 1700 -
TmTe-Sb 10 TmTe 810 -
TmSb4Te7-Sb 90 Sb 750 2 Sb
TmSb4Te7- Tm3Te4 13 Tm3Te4 790 3 Tm3Te4
Join Sb2Te3-Tm is no pseudo-binary and inter- Sb-TmSb-TmTe (III) and TmSb-Tm-TmTe (IV) sects four subordinate (secondary) ternary systems: (Fig.1). Sb2Te3-Sb-TmSb4Te7 (I), Sb- TmSb4Te7-TmTe (II),
In the Sb2Te3-TmTe system [6], two compounds are formed, TmSb4Te7(S1) and TmSb2Te4(S2). The former compound melts congruently at 875 K, and the latter melts incongruently at 1050 K. Eutectic coordinates are 15 mol% TmTe at 850 K and 42 mol% TmTe at 835 K. In the Sb2Te3-Tm2Te3 system for the 1:1 composition, the ternary TmSbTe3(S3) compound is former by a peritectic reaction at 1335 K [7]. Eutectic cordinates are 15 mol% Tm2Te3 and 750 K. For both systems, solid solubility in Sb2Te3 is up to ~5 mol% at room temperature.
Here, we report experimental data on the joins Sb2Te3-Tm3Te4, TmSb-TmTe, TmSb4Te7(S0-Tm3Te4, TmSb4Te7(S1)-Sb, TmTe-Sb, Sb2Te3-Tm, and TmSb4Tev(S:)-Te.
Investigations demonstrated that the joins Sb2Te3-Tm3Te4, TmTe-Sb, TmSb-TmTe, TmSb4Te7-Sb, and TmSb4Te7- Tm3Te4 are pseudo binary of a simple eu-tectic type. Selected data on these joins are listed in Table 1.
The part of the join within subordinate system I is characterized by the formation of phases at 800,750, and 700 K, respective, and by a three-phase nonvariant equilibrium at 550 K. The reactions proceeding at these points are listed in Table 2.
The liquidus surface of subordinate system II includes the region of primary crystallization of compounds TmSb4Te7, TmSb2Te4, and TmTe.
In this part of the join, the peritectic reaction L + TmTe-^- TmSb2Te4 + Sb proceeds at 680 K, and the ternary eutectic Sb + TmSb2Te4 + TmSb4Te7 crystallizes at 600 K.
The liquidus surface of subordinate system III includes the field of primary crystallization of TmTe.
Eighteen fields of primary crystallization are dawn in the ternary system. Of these, three fields correspond to the primary crystallization of the terminal components, and their surface is diminished in the series Sb ^ Tm ^ Te. The most extensive region in the diagram is the field of the TmTe phase (-52 mol %), and the least extensive one is the field of Te.
There are 16 nonvariant equilibria in the Tm-Sb-Te system. Of these, E1-E7 are ternary eutectic points,
and P1-P8 are peritectic points. Chemical reactions that proceed at these equilibrium nonvariant points are listed in Table 2.
From the comparison of investigation of ternary systems Tm-Sb-Te, Sm-Sb-Te, Sm-Sb-Te, and Sm-Bi-Te [8-11], an inference can be made that ternary compounds of compositions LnB2VX4, LnB4VX7, and LnBVXs (Ln=REE; BV=Sb,Bi; X=Se,Te) are formed in all systems. The LnX phase has the most extensive crystallization field in the systems (>50 mol %).
The following nonvariant processes occur in the solidus:
L+TmSb~TmTe+TmSb2 at 1100 K, L~Sb+TmTe+TmSb2 at 650 a K. The part of the join that passes through subordinate system IV has a complex character.The liquidus of this part consist of the primary crystallization curves of thulium monotelluride and metal thulium. Thermal events at 1400 and 1200 K are associated with the formation of binary compounds Tm4Sb3 and Tm5Sb3 by peritectic reactions indicated in Table 2.
Table 2
Nonvariant equilibria in the Tm-Sb-Te
Point Reaction T,K Point Reaction T,K
Ei L-^Tm+Tm5 Sb3+TmTe i000 P3 L ii00
E2 L~Sb+TmSb2+TmTe 650 P4 L 750
E3 L~Sb+Si+S2 600 P5 L 700
E4 L~Si+ß+ß' 550 P6 L 650
E5 L-^TmTe+S2+Tm3Te4 675 P7 L 600
E6 L^Si+Sb2Te3+Tm3Te4 650 P8 L 625
E7 L^ Sb2Te3+TmTe3+Te 550 P9 L 700
Pi L+Tm4Sb3^TmTe+Tm5Sb3 i200 Pi0 L 875
P2 L+TmSb i400 L
Alloys in this part of the join solidify at a ternary eutectic point by the reaction L+-^-TmTe+ TmsSb3+Tm at 1000 K.The solubility of thulium in Sb2Te3 is ~3 mol % at 300 K and ~4 mol % at 800 K.
Join TmSb4Te7-Te is nonpseudo-binary and intersect three subordinate ternary systems: TmSb4Te7-Sb2Te3-Tm3Te4, Sb2Te3- Tm3Te4-Tm2Te3 and Sb2Te3-Tm2Te3-Te.
The liquidus line of the join includes six primary crystallization curves of the phases TmSb4Te7-based a' solid solition, Sb2Te3, TmSbTe3, TmTe2, TmTe3 and Te. DTA peaks at 675,625 and 600 K correspond to the
formation of TmSbTe3, TmTe2 and TmTe3 compounds, respectively. Peaks at 650 and 550 K are duet o three-phase autectic equilibria in ternary systems intersecting the join:
L^ a'+ Sb2Te3+ Tm3Te4 L^ Sb2Te3+ TmTe3+Te. The region of a' solid solutions extends to 3 mol % Te at 300 K.
The liquidus-surface projection of the Tm-Sb-Te system (Fig. 2) is constructed from the literature data on binary systems and the results of investigation of seven pseudo-binary and two nonpseudo-binary joins.
The Tm-Sb-Te system is triangulated into eight secondary ternary systems:
TmSb-Tm-TmTe, TmSb-Sb-TmTe, Sb-S:-TmTe, Sb- S1- Sb2Te3
S1-TmTe-Tm3Te4, S1- Sb2Te3- Tm3Te4, Sb2Te3-Tm3Te4-Tm2Te3 and Sb2Te3- Tm2Te3-Te.
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