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UDC 546(681.22+ 65.22)
THE TERNARY SYSTEM La2S3-Ga2S3-EuS AND GLASS FORMATION
I.B.Bakhtiyarly, A.S.Abdullayeva, R.D.Kurbanova, R.I.Karimov
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
[email protected] Received 18.04.2016
By the methods of differential thermal, X-ray phase, microstructural analyses and microhardness and alloy density testing, phase equilibria in a ternary system La2S3-Ga2S3-EuS have been investigated. The phase diagrams of some polymeric cuts and projections of liquidus surface were plotted. The regions of primary crystallization of all phases as well as coordinates of all non- and mono-variant equilibria were established in the studied.
Keywords: system, physico-chemical research, phase diagram, glassformation, non- and monovariant equilibria.
Introduction
The optical transparency of a great number of crystalline materials in the visible regions and IR spectrum may serve as the basis for their application. Of primary concern among a wide variety are compound chalcogenide lanthanides, i.e. activated EuGa2S4:Ln3+, which have Anti-Stokes luminescent properties [1], native to good results reproducibility, wide operating region of optical transparency. Therefore, knowledge about the character of physicochemical interaction in the ternary system La2S3-Ga2S3-EuS opens up possibilities for synthesis of new materials with predicted properties.
The sides of the above-mentioned ternary system La2S3-Ga2S3 are quazibinary [2, 3] a congruently melting compound La6Ga10/3S14 is formed at 1425 K, but by peritectic reaction (L+La6Ga10/3S14 o- LaGaS3) forming LaGaS3 takes place at 1225 K. In the system there are two eutectic points, with coordinates, corresponding to 20 mol.% of La2S3 at 1140 K and 80 mol.% of La2S3 at 1395 K.
According to data [4], the system EuS-Ga2S3 is quazibinary with singular congruently melting compound EuGaS4. The work [5, 6] has indicated that the formation of two congruently melting ternary compounds was observed in the system: EuGa2S4, EuGa4S7 melting at 1490 and 1400 K, respectively.
The authors [7] have determined that the singular compound with the composition of EuLa2S4 was formed in the system EuS-La2S3.
The compound EuLa2S4 is congruently melted at 2360 K and forms eutectic with initial components. The eutectic has the composition of 63 mol.% of EuS between EuS and EuLa2S4 and is melted at 2200 K. The coordinates of eutectic point between EuLa2S4 and EuS are 27 mol.% of EuS and 2060 K.
It was also found out that the internal partially quasibinary cut LaGaS3-EuGa2S4, where the compound with the composition of EuLaGa3S7 (congruently melted) is obtained, was crystallized in the tetragonal syngony [8]. The compound EuLaGa3S7 participates in the triangulation of the triangle La2S3-Ga2S3-EuS.
Experimental part
In our experiments as initial components monoclinic Ga2S3 [9], synthesized from elements was used. As La2S3 and EuS, there was used an ultimate product, produced by the plant method. According to reference data, both compounds are crystallized in the cubic syngo-ny, La2S3 of which - in the structure type of P-Nd2S3 [10], EuS - in the structure of NaC1 [11].
The investigations were carried out by the methods of differential thermal (DTA), X-ray phase (RFA), microstructural analyses (MSA) and microhardness and density testing.
DTA was studied by device STA 429 CD (NETZSCH, Germany, combined with mass-spectrometer MSM4033C) in the system of synchronous thermal analysis. Accuracy of determining temperature of heat effects made ±1°C to 15000C. Rate of heating and cooling was
found to be 10 C/min. On constructing phase diagram we used the data obtained on curves of heating.
X-ray diffraction analysis of the system was performed on automatic diffractometer "D2 Phaser" (Brucker, Germany).
The results, given below, relate to the alloys annealed during 600 h at temperatures 500 lower than the solidus.
Results and their discussion
The investigations found out that in the present ternary system seven quazibinary cuts triangulate it into seven pseudoternary systems: La6Ga10/3S14-Ga2S3-EuLaGa3S7, EuLaGa3S7-EuGa4S7, EuLaGa3S7-EuGa4S7-EuGa2S4, La2S3-La6Ga10/3S14-EuLaGa3S7, La2S3-EuLaGa3S7-EuLa2S4, EuLa2S4-EuLaGa2S4, EuLa2S4-EuGa2S4-EuS.
Below we outline briefly interaction proceeding in the ternary system La2S3-Ga2S3-EuS according to separate cross-sections.
The cut 3Ga2S3-EuLaGa3S7 is quazibi-nary and its state diagrams refers to eutectic type [12], the coordinates of the eutectic point (e3): 80 mol.% of EuLaGa3S7 at the temperature of 1020 K. The breakdown of y-solid solution with formation of P-solid solution on the basis of Ga2S3 occurs eutectoidly, in response to Eu-LaGa3S7, the transition temperature is reduced to 1150 from 1295 K. In the part of Ga2S3 the solubility at room-temperature reaches 3 mol.% of EuLaGa3S7 and on the basis of EuLaGa3S7 reaches 1.5 mol.% of Ga3S3.
The cut EuLaGa3S7-EuGa4S7 [13] is a quazibinary section of the ternary system La2S3-Ga2S3-EuS and refers to the eutectic type; the coordinates of the eutectic point (e4): 47 mol.% of EuGa4S7 and 1040 K. The solubility is found on the basis of both components. The solubility on the basis of EuLaGa3S7 covers to 2 mol.% of EuGa4S7 and on the basis of Eu-LaGa4S7 to 1.5 mol.% of EuLaGa3S7 at room temperature.
The cut La6Ga10/3S14-EuLaGa3S7 is qua-zibinary and of its state diagrams refers to the eutectics type. Liquidus of the cut consists of regions of primary crystallization: La6Ga10/3S14 and EuLaGa3S7 being intersected in the double non-variant eutectic point (e7) with the coordi-
nates of 73 mol.% of EuLaGa3S7 and 1080 K. The reciprocal solubility also limited at room temperature reaches 5 mol.% of EuLaGa3S7 and 3 mol.% of La6Ga10/3S14.
The cut EuLaGa3S7-EuGa2S4 is quazibinary of eutectic type. The eutectic point (e6) corresponds to the composition of 18 mol.% of EuLaGa3S7 and 1170 K. The reciprocal solubility of components at room temperature reaches 3 mol.% of EuLaGa3S7 and 4 mol.% of EuGa2S4.
The cut 3 La2S3-EuLaGa3S7 [14] is also quazibinary. Liquidus is represented by two intersection branches of primary crystallization: La2S3 and EuLaGa3S7. The melting temperature of the eutectic (e8) is 1090 K; the composition is 16 mol.% of La2S3. No solubility on the basis of initial components was practically found.
The cut 3 EuLa2S4-EuLaGa3S7 [14] is quazibinary, of the eutectics type. The eutectic (e9) has the composition of 74 mol.% of EuLaGa3S7 and 1085 K. No solubility on the basis of initial components was determined.
The cut EuLa2S4-EuGa2S4 [15] is the quazibinary section of the ternary system La2S3-Ga2S3-EuS and its state diagram refers to the eutectic type; the coordinates of the eu-tectic point (e10): 24 mol.% of EuLa2S4 and 1300 K. The solubility on the basis of EuLa2S4 is 4 mol.% of EuGa2S4 at room temperature.
In order to determine the coordinates of non-variant points in the ternary system La2S3-Ga2S3-EuS, the polythermal section was investigated. The state diagram of some characteristic peculiar polythermal section is shown in Figure 1-3.
The cut (Ga2S3)0.75(EuS)0.25(e2)-
(Ga2S3)0.20(La2S3)0.80 (e^) [16] is the non-quazibinary section (Figure 1) of the ternary system La2S3-Ga2S3-EuS. It intersects these subordinate of triangle: La2S3-La6Ga10/3S14-EuLaGa3 S7, La6Ga10/3 S 14-EuLaGa3 S7-Ga2S3, Ga2S3-EuLaGa3 S7-EuGa4S7.
Liquidus of the system is illustrated by three regions of primary crystallization of phases. First, a' solid solution is separated on the basis of La6Ga10/3S14. Then begins primary crystallization of the compound LaGaS3 followed by crystallization of P-Ga2S3.
T, K 1800
1600
1395
(Ga2S3)0.75(EuS)0.25
(e2)
20 40 60 80 (Ga2S3)0.20(La2S3)0.80
mol.% (ei2)
Fig. 1. Phase diagram of the (Ga2S3)0.75(EuS)0.25 (e2)-(Ga2S3)0.20(La2S3)0.80 (ei2). a - EuLaGa3S7, ß - Ga2S3, ß' - EuGa2S4, y' - EuGa2S4, 6 - EuLa2S4.
In the part of the cut intersecting the ternary system La2S3-EuLaGa3S7-La6Ga1o/3S14, the alloys terminate the crystallization in the ternary eutectic point E6 at 1030 K. Below the eutectic horizontal samples consist of three phases: La2S3, a (EuLaGa3S7), a'(La6Ga10/3S14).
The interaction in the part of the cut passing through the subordinate ternary system La6Ga10/3S14-EuLaGa3S7-Ga2S3 is a relatively complecated, i.e. the formation of a peritectic phase occurs there. The liquidus of this part consists of three lines of initial phase isolation. The isothermal horizontal at 1050 and 900 K, respectively, reflects the peritectic and eutectic equilibria.
The third part of the cut intersects the secondary ternary system EuLaGa3S7-EuGa4S7-Ga2S3.
The liquidus of this part consists of a singular line, primary crystallization of P-Ga2S3.
In the part of the cut crystallization is terminated at the temperature of the ternary eu-tectic (E2) 985 K.
The cut EuLaGa3S7-LaGaS3 being a non-quazibinary section intersects two surfaces of the primary crystallization a(EuLaGa3S7) and a'(La6Ga10/3S14). Therefore, the liquidus of this cut consists of two curves - the beginning of
crystallization a(EuLaGa3S7) and a' (La6Ga10/3 S14), which are intersected in one point, there begins the secondary crystallization [m+a(EuLaGa3S7)+ a'(La6Ga10/3S14)], corresponding to 54 mol.% of LaGaS3 at the temperature of 1200 K.
After the primary crystallization a'(La6Ga10/3S14) a three-phase peritectic reaction takes place: L+a'(La6Ga10/3S14)o-LaGaS3. The initial temperature of this transformation gradually falls to 1225 from 1050 K.
The solidus of the cut EuLaGa3S7-LaGaS3 starts horizontally passing at 1050 K, which corresponds to the temperature of the four-phase reaction L+a(La6Ga10/3S14)o-LaGaS3+a(EuLa6GaS7).
So crystallization in all alloys of this cut is terminated with a non-variant, peritectic process.
The cut (Ga2S3)0.75(EuS)0.25(e2)-
(EuGa2S4)0.76(EuLa2S4)0.24 (e10) is the non-qua-zibinary section (Figure 2) of the ternary system La2S3-Ga2S3-EuS. It intersects three secondary triangles [16]. Its state diagram consists of three parts. The liquidus of the system consists of two regions of primary crystallization of phases P'(EuGa4S7) and P'(EuGa2S4).
Isometric horizontals at 985, 1000 and 1025 K characterize the eutectic equilibria E2, E3, E4, respectively.
T, K
1300
(Ga2S3)o.75(EuS)o.25
(e2)
20
40
mol. %
60
80
(EuGa2S4)0.76(EuLa2S4)0.24 (e10)
Fig. 2. Phase diagram of the (Ga2S3)0.75(EuS)025-(EuGa2S4)07 6(EuLa2S4)0.24. a - EuLaGa3S7, ß - Ga2S3, ß' - EuGa2S4, Y - EuGa2S4, 6 - EuLa2S4.
The cut La6Ga10/3S14-
(Ga2S3)0.28(EuS)0.72 (e11) is the non-quazibinary section (Figure 3), intersecting four subordinate triangles: La6Gai0/3Si4-EuLaGa3S7-La2S3, La2S3-EuLaGa3S7-EuLaS4, EuLa2S4-EuLaGa3S7- Eu-Ga2S4, EuLa2S4-EuGa2S4-EuS and four areas of primary crystallization. Therefore, its li-quidus is illustrated by four curves corresponding to the temperatures of primary isolation of crystals a'(La6Ga10/3S14), La2S3, EuLa2S4 and EuS.
In the part of the cut intersecting the ternary system EuLaGa3S7-La6Ga10/3S14-La2S3 a a' solid solution is preliminarily isolated on the basis of La6Ga10/3S14. Afterwards the primary crystallization La2S3 starts. Crystallization of alloys is terminated at the temperature of 1030 K, being to the temperature of ternary eutectic. Below the eutectic horizontal, the samples consist of three phases: a'+a+La2S3 (a-EuLaGa3S7). In this part of the system there are solidites on the basis of La6Ga10/3S14 1.5 mol.% of e11.
In the part of the cut intersecting the ternary system La2S3-EuLaGa3S7 the crystallization is terminated in ternary eutectic E6 at the temperature of 1050 K.
In the third part of the cut intersecting the ternary system EuLaGa3S7-EuLa2S4-EuGa2S4 the alloys terminate crystallization in ternary eutectic E4 at the temperature of 1025 K, and in the part of the cut intersecting the ternary system EuLa2S4-EuS-EuGa2S4 the alloys terminate crystallization in ternary eutectic at the temperature of 1220 K. Below the eutectic horizontal, the samples consist of three phases: EuS+EuLa2S4+Y'(EuGa2S4).
The projection of the liquidus surface of the ternary system La2S3-Ga2S3-EuS. Relying on the obtained results under the above-mentioned systems as well as references quoted, we plotted the projection of the liquidus area of the ternary system La2S3-Ga2S3-EuS (Figure 4).
The monovariant equilibrium curves were plotted according to the internal cross sections, corresponding curves to the primary crystallization of phases of the systems under study.
The points of non-variant equilibrium were obtained with the extrapolation of direction of monovariant equilibrium curves (Table). By graphic interpretation isotherms were plotted every 200 K, sometimes 100 K.
The ternary system has nine fields of primary crystallization of separate phases.
T, K
Y'(EuGa2S4) a'(La«Gaio/3Si4
1600
1425 1400
1200
1000
800
a
r
PJ j
+ $
<-i Ol
«S4 UJ
-j +
+ —
La^GaiotfSn 9La2S;) 5Ga2S3
40 60
mol%
80 (Ga2S3W(EuS)c,72 14eH
Fig. 3. Phase diagram of the La6Gaio/3Si4-(Ga2S3)o.2s(EuS)o.72.
EuLa,S4
EuS
Fig. 4. Projection of the liquidus surface of the system La2S3-Ga2S3-EuS: 1 - y(Ga2S3), 2 - ß(Ga2S3), 3 - LaGaS3, 4 - a(EuLaGa3S7), 5 - ß'(EuGa4S7), 6 - a'(La6Gaio/3 SM), 7 - 0[(La2S3)i_J((EuLa2S4)JC], 8 - y'(EuGa2S4), 9 - EuS, 10 - 0'[(La2S3)i_J((EuLa2S4)JC]i.Ji(EuLaGa3S7)J,.
Non-variant equilibria of the ternary system La2S3-Ga2S3-EuS
Symbols Equilibrium Composition, mol.% T, K
La2S3 Ga2S3 EuS
ei L~ß(Ga2S3)+La2GaS3 20.0 80.0 - ii40
e2 L~ß(Ga2S3)+ß'(Eu Ga4S7) - 75.0 25.0 i295
ез L~ß(Ga2S3)+a(EuLnGa3S7) i3.3 60.0 26.7 i020
e4 L~ß(EuGa4S7)+a(EuLnGa3S7) 33.3 57.8 8.9 i040
es L~ß'(EuGa4S7)+y'(EuGa2S4) - 60.0 40.0 i320
ее L~y'(EuGa2S4)+a(EuLaGa3S7) 9.0 50.0 4i.0 i070
ev L-^-a'(La6Gai0/3Si4)+a(EuLaGa3 S7) 29.5 46.2 24.3 i080
ев L~9[(La2S3)i-x(EuLa2S4)x; x=0]+a(EuLaGa3S7) 30.0 42.0 28.0 i090
e9 L^9[(La2S3)i-x(EuLa2S4)x; x=1]+a(EuLaGa3S7) 25.3 37.0 37.7 i085
ei0 L^9[(La2S3)i-,(EuLa2S4),; x=il+y'(EuGa2S4) i2.0 38.0 50.0 i330
eii L~y'(EuGa2S4)+EuS - 33.0 67.0 i390
ei2 L^a'(La6Gaio/3Si4)+0[(La2S3)i-x(EuLa2S4)x; x=0] 80.0 20.0 - i395
ei3 L~9[(La2S3)i-x(EuLa2S4)x; x=i]+EuS 73.0 - 27.0 2065
P L^a'(La6Gai0/3Si4)^LaGaS3 3i.5 68.5 - i225
Ei L~LaGaS3+a(EuLaGa3S7)+ß(Ga2S3) i6.5 58.5 25.0 900
E2 L~ß(Ga2S3)+ß'(EuGa4S7)+a(EuLaGa3S7) i0.5 59.0 30.5 985
Ез L~ß(EuGa4S7)+a(EuLaGa3S7)+y'(EuGa2S4) 8.5 55.5 36.0 i000
E4 L~y'(EuGa2S4)+a(EuLaGa3S7)+ 9[(La2S3)i-x(EuLa2S4)x] i6.0 39.5 44.5 i060
Es L~9[(La2S3)i-x(EuLa2S4)x]+EuS+y'(EuGa2S4) 7.5 36.5 56.0 i220
Еб L~9[(La2S3)i-x(EuLa2S4)x]+a'(La6Gai0/3Si4)+a(EuLaGa3S7) 28.5 39.0 32.5 i050
P L+a'(La6Gai0/3Si4)+LaGaS3+a(EuLaGa3S7) 25.0 53.0 22.0 i050
In the system there are 16 curves of mono-variant equilibrium and 7 points of non-variant equilibrium, E1-E6 of which are ternary eutectic points; one is a ternary peritectic point. The reaction taking place in the indicated non-variant points is given in the Table.
The congruent and incongruent processes, which take place on the curves of mono-variant equilibrium, are easy to recognize, using the data given the Table and Figure 4.
Besides, we studied in the system the dependence of glass formation on the composition and its borders were determined [17]. As glasses have the similar structure with different type alloys, glass formation field is not directly observed in phase diagrams. It is determined by differential-integral equilibria. By using the parameters of physical-chemical equilibria in state diagrams it is possible to determine structural unit of formed glasses, kinetic relation of them with initial components, the effect of solid solutions, monotectics on glass formation. That's why we consider that parallel study of state diagram of La2S3-Ga2S3-EuS ternary system with glass formation field is scientifically and practically important.
In the work to determine glass formation fields in the system, the samples were synthesized from initial components at 1425 K, in "glass-graphite crucible" placed in specially assembled quartz reactor. Sharp cooling process of samples was conducted by dropping them into the water from synthesis temperature. Obtained samples were studied by physical-chemical analysis methods (DTA, DTG, X-ray phase). Samples are stable to the influence of air, water and organic solvents at room temperature. They partially decompose by the effect of alkali and mineral acids.
When heated they are fully dissolved in chromium mixture (chrompic). Color of glass changes from gold-yellow to grey-black when moves from Ga2S3-La2S3 towards Ga2S3-EuS. In projection of liquidus surface of quasiternary La2S3-Ga2S3-EuS system the dependence of glass formation field on the composition is presented (Figure 4).
In the Figure transparent glass field (mm2 and m[m[) was limited with nontransparent band from both sides. Presence of crystal centers in nontransparent glass field was confirmed by X-
ray phase analysis. DTA shows that in the glass containing (Ga2S3)o.65(La2S3)o.35 tg= 895 K, tk=950 K, but in the glass containing (Ga2S3)o.7o(EuS)o.3o tg=835 K, tk=855 K. Depending on amount of EuS ternary glasses value of tg decreases from 895 to 835 K, value of tk decreases from 89o to 855 K, correspondingly, value of Hp, increases from 520 to 560 mPa.
Thus, for the first time the projection of liquidus area of the ternary system La2S3-Ga2S3-EuS has been plotted. The regions of primary crystallization of phases have been found as well as the coordinates of all the non- and monovari-ant equilibria of the system under study.
In the system glass formation borders were determined and physical and chemical properties of obtained new were studied
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La2S3-Ga2S3-EuS U£LU SISTEMi УЭ §U§OaMaLaGOLMa
LB.Baxtiyarli, A.S.Abdullayeva, R.C.Qurbanova, RLKarimov
Differensial termiki, rentgenfaza mikroqurulu§ analizlari, mikrobarkliyin va sixligin olgulmasi ila La2S3-Ga2S3-EuS uglu sisteminda faza tarazligi tadqiq edilmi§, bir nega politermik kasiklarin faza diaqrami va likvidius sathinin proyeksiyasi qurulmu§dur. ilkin kristalla§ma sahalari, non- va monovariant tarazliqlann koordinatlan muayyan edilmi§dir. Hamginin sistemda §u§aamalagalma sahasinin sarhadlari daqiqla§dirilmi§, alinan fazalann fiziki-kimyavi xassalari 6yranilmi§dir.
Agar sozlar: sistem, fiziki-kimyavi xassslsr, faza diaqrami, gugssmslsgslms, non- vs monovariant tarazliqlari.
ТРОЙНАЯ СИСТЕМА La2S3-Ga2S3-EuS И СТЕКЛООБРАЗОВАНИE
И.Б.Бахтиярлы, А.С.Абдуллаева, Р.Д.Курбанова, Р.И.Керимов
Методами дифференциально-термического, рентгенофазового, микроструктурного анализов и измерения микротвердости, плотности сплавов исследованы фазовые равновесия в тройной системе La2S3-Ga2S3-EuS. Построены фазовые диаграммы некоторых политермических разрезов и проекции поверхности ликвидуса. Установлены области первичной кристаллизации всех фаз, а также координаты всех нон- и моновариантных равновесий в исследуемой системе. Определены границы области стеклообразования в системе La2S3-Ga2S3-EuS и изучены некоторые физико-химические свойства полученных фаз.
Ключевые слова: система, физико-химического свойства, фазовые диаграммы, стеклообразование, нон- и моновариантные равновесия.
