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Quasi-ternary system Cu2GeS3–Cu2SnS3–CdS
Journal of Alloys and Compounds 484 (2009) 147–153
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Quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS L.P. Marushko ∗ , L.V. Piskach, O.V. Parasyuk, I.A. Ivashchenko, I.D. Olekseyuk Department of General and Inorganic Chemistry, Volyn National University, Voli Ave 13, Lutsk 43025, Ukraine
a r t i c l e
i n f o
Article history: Received 10 April 2009 Received in revised form 27 April 2009 Accepted 27 April 2009 Available online 3 May 2009
a b s t r a c t Phase equilibria in the quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS were investigated by differential thermal analysis and XRD. Isothermal section of the system at 670 K, liquidus surface projection and the perspective views of the phase diagram were constructed. The boundaries of solid solution ranges of the system components and the intermediate phases were determined. © 2009 Elsevier B.V. All rights reserved.
Keywords: Semiconductors X-ray diffraction Thermal analysis
1. Introduction The quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS was investigated with a view to the formation of solid solution ranges of the quaternary compounds Cu2 CdGeS4 and Cu2 CdSnS4 which have semiconductor and optoelectronic properties [1–3]; this would allow one to obtain materials with a gradual modification of such properties. The AI 2 BII DIV X4 compounds that form in this system crystallize in two structures, orthorhombic wurtzite-stannite type ¯ (space group (s.g.) Pmn21 ) and tetragonal stannite type (s.g. I 42m) [4–6]. Noncentro-symmetrical structures are promising for the use in non-linear optics. The use of copper-containing phases Cu2 BII DIV X4 as solar cell materials is also feasible. Such materials must be semiconductors with the bandgap energy E = 1.1–1.5 eV. Cu2 BII DIV X4 compounds are isoelectronic analogs of CuInSe2 (by the substitution 2In → Cd + Ge) and possess the necessary properties. Considering p-type conductivity and the required bandgap values (e.g. 1.37 eV for Cu2 CdSnS4 [7]), the compounds are promising materials for the conversion of solar and polarized radiation in the heterojunctions with wide-gap BII X semiconductor with n-type conductivity. 2. Quasi-binary systems 2.1. The Cu2 GeS3 –CdS system The phase diagram of the Cu2 GeS3 –CdS system is presented in [8]. The system is quasi-binary, with the formation of two quater-
∗ Corresponding author. Tel.: +38 03322 49467; fax: +38 03322 41007. E-mail address: [email protected] (L.P. Marushko). 0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2009.04.128
nary compounds, Cu2 CdGeS4 and Cu2 Cd3 GeS6 . The former forms in the peritectic process L + Cu2 Cd3 GeS6 ⇔ Cu2 CdGeS4 at 1282 K and has a narrow homogeneity region. The eutectic of Cu2 GeS3 and Cu2 CdGeS4 has the coordinates of 16 mol.% CdS and 1229 K. The other quaternary phase, Cu2 Cd3 GeS6 , forms at 1329 K; its composition, as determined by the magnitude of endothermal effects, falls at 75 mol.% CdS. The phase is unstable and decomposes at 1134 K. The solid solution ranges of the system components do not exceed 2 mol.%. The Cu2 CdGeS4 compound crystallizes in the wurtzite–stannite structure type (s.g. Pmn21 ) with unit cell parameters a = 0.77024, b = 0.65486, c = 0.62928 nm [5]. The bandgap energy of Cu2 CdGeS4 equals 2.05 eV at 290 K, with the hole conduction [9]. The thermoEMF coefficient reaches 1800 V/K; combined with low thermal conductivity, the compound may be promising for thermoelectronic applications [2].
2.2. The Cu2 SnS3 –CdS system The quasi-binary system Cu2 SnS3 –CdS was investigated in [10]. The quaternary compound Cu2 CdSnS4 that forms in the system melts incongruently at 1178 K. The eutectic point of Cu2 CdSnS4 and Cu2 SnS3 has the coordinates of 15 mol.% CdS and 1126 K. The solid solution range of Cu2 SnS3 extends to 10 mol.% CdS at 1126 K, and to 8 mol.% CdS at 820 K. The solid solution range of CdS includes 6 mol.% Cu2 SnS3 at 1178 K and decreases with lower temperature. The quaternary compound Cu2 CdSnS4 melts at 1187 K according to [11], and at 1199 K according to [7]. ¯ Cu2 CdSnS4 crystallizes in the stannite structure type (s.g. I 42m) with unit cell parameters a = 0.5586, c = 1.0834 nm [6]. The bandgap energy of Cu2 CdSnS4 equals 1.4 eV at 290 K. This compound is also characterized by p-type conductivity [3].
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L.P. Marushko et al. / Journal of Alloys and Compounds 484 (2009) 147–153 stage the ampoules were heated in oxygen-gas burner flame to complete bonding of elementary sulfur. The second stage was performed in a shaft-type furnace. The alloys were heated at the rate of 50 K/h to the maximum temperature set at 50–100 K above the melting points of the components. After the exposure to the maximum temperature for 2–3 h the alloys were slowly cooled at the rate of 10 K/h to 670 K. The samples were annealed at this temperature for 500 h, followed by quenching into cold water. The synthesis resulted in compact dark-grey ingots. Obtained alloys were investigated by differential thermal analysis (PaulikPaulik-Erdey derivatograph, Pt/Pt-Rh thermocouple) and XRD (DRON 4–13 diffractometer, Cu K␣ radiation, Ni filter, /2 scanning in the angle range 10◦ ≤ 2 ≤90◦ , scan step of 0.05◦ , scan time 1 s). The computation of unit cell parameters of the studied samples was performed using PDWin-2 software package.
4. Results 4.1. Isothermal section of the Cu2 GeS3 –Cu2 SnS3 –CdS system
Fig. 1. Phase diagram of the Cu2 GeS3 –Cu2 SnS3 system (1, L; 2, L + ␣; 3, ␣).
2.3. The Cu2 GeS3 –Cu2 SnS3 system The Cu2 GeS3 –Cu2 SnS3 system was investigated by us earlier [12]. The system components form a continuous solid solution series. The phase diagram belongs to Type III of Roozeboom classification. During the construction of the liquidus surface projection of the quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS we refined the phase diagram of the Cu2 GeS3 –Cu2 SnS3 system (Fig. 1). Namely, the minimum coordinates are ∼66 mol.% Cu2 SnS3 and 1125 K.
From the results of X-ray phase analysis of the alloys of the Cu2 GeS3 –Cu2 SnS3 –CdS system, the isothermal section at 670 K was constructed shown in Fig. 2. The existence of four single-phase regions was established in the system at this temperature. They are: the continuous solid solution series of Cu2 GeS3 and Cu2 SnS3 (␣-solid solutions); solid solutions of the quaternary compounds stretched along the Cu2 CdGeS4 –Cu2 CdSnS4 section: ␥-solid solution range of Cu2 CdGeS4 with the orthorhombic structure which extends to 9 mol.% Cu2 CdSnS4 , and ␦-solid solution range of Cu2 CdSnS4 with the stannite structure which extends to 14 mol.% Cu2 CdGeS4 ; and -solid solution range of CdS with the wurtzite structure. Another -solid solutions range of Cu2 Cd3 GeS6 is absent from the isothermal section at 670 K as -solid solutions undergo eutectoid decomposition below 1125 K. Additionally, five two-phase regions and two three-phase regions exist in the system at the annealing temperature. 4.2. The Cu2 Cd3 GeS6 –Cu2 CdSnS4 section
3. Experimental The investigation of phase equilibria in the Cu2 GeS3 –Cu2 SnS3 –CdS system was performed using 88 alloys, their compositions are presented in Fig. 2. The alloys were synthesized from high-purity elements (at least 99.99 wt.% of the principal element). Calculated amounts were placed into quartz ampoules that were evacuated to 10−1 Pa and soldered. The synthesis was performed in two stages. At the first
The vertical section Cu2 Cd3 GeS6 –Cu2 CdSnS4 is presented in Fig. 3. The section was studied to determine the boundaries of the invariant processes, peritectic LU1 +  ⇔ ␦ + (Fig. 9) and eutectoid ⇔  + ␥ + ␦, that occur in the system. The section liquidus consists of the curve of the primary crystallization of -solid solutions. Cu2 CdSnS4 forms in a peritectic process at 1193 K. The section crosses the plane of the invariant peritectic process LU1 +  ⇔ ␦ + at 1187 K. The curve ab coincides with the polytherm of the solubility of -solid solutions, therefore single-phase field borders on the three-phase field L +  + . The alloys below 1187 K are three-phase ( + ␦ + ) as the peritectic process leads to the depletion of the liquid. The alloys of the section undergo a monovariant eutectoid process ⇔  + ␥ + ␦ at 1125 K. Its existence is caused by the decomposition of Cu2 Cd3 GeS6 . The composition of -solid solutions during the monovariant eutectoid process follows the curve cd, therefore the single-phase region of -solid solutions borders on the three-phase field  + ␥ + . The majority of the alloys below 1125 K are three-project and contain the crystals of -, ␥- and ␦solid solutions. 4.3. The Cu2 CdGeS4 –Cu2 CdSnS4 section
Fig. 2. Isothermal section of the Cu2 GeS3 –Cu2 SnS3 –CdS system at 670 K, phase and chemical composition of alloys.
The vertical section Cu2 CdGeS4 –Cu2 CdSnS4 was constructed from DTA and XRD results (Fig. 4). The section was studied to determine the exact position of the monovariant line p1 U1 (Fig. 9), the solid solubility ranges of the quaternary compounds, and the boundaries of the invariant peritectic processes that occur in the system.
L.P. Marushko et al. / Journal of Alloys and Compounds 484 (2009) 147–153
Fig. 3. Vertical section Cu2 Cd3 GeS6 –Cu2 CdSnS4 (1, L; 2, L + ; 3, L +  + ; 4, L +  + ␦; 5, ; 6,  + ␦ + ; 7,  + ␦; 8,  + ␥ + ; 9,  + ␥; 10,  + ␥ + ␦; 11, ␦).
The section liquidus is represented by the primary crystallization of -solid solutions (curve ab) and -solid solutions (curve bc). The section crosses the plane of the invariant peritectic process LU1 +  ⇔ ␦ + (Fig. 9) at 1187 K forming the horizontal line de. The regions of the co-existence of three phase L +  + and L +  + ␦ converge to this line. Below the line de we find the region of the monovariant eutectic process L ⇔ ␦ + ; this, together with the region of the monovariant peritectic process L + ⇔ ␥, converge to the segment fg. This horizontal line belongs to the plane of the invariant peritectic process LU2 + ⇔ ␥ + ␦ (Fig. 9) that takes place at 1176 K. The segment fg coincides with the connect-
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Fig. 4. Vertical section Cu2 CdGeS4 –Cu2 CdSnS4 (1, L; 2, L + ; 3, L + ; 4, L +  + ; 5, L +  + ␦; 6, L + ␥ + ; 7, L + ␦ + ; 8, L + ␦; 9, ␥; 10, ␦; 11, ␥ + ␦).
ing line of this plane, therefore the section alloys are two-phase (␥ + ␦) below 1176 K. The extent of ␥-solid solutions at this temperature is 11 mol.% Cu2 CdSnS4 , that of ␦-solid solutions is 16 mol.% Cu2 CdGeS4 . The solid solution ranges vary little with temperature, and equal 9 mol.% for ␥-solid solutions and 14 mol.% for ␦-solid solutions at 670 K. The ranges of solid solutions were determined from the change of unit cell parameters of alloys (Fig. 5). 4.4. The ‘Cu2 Ge0.75 Sn0.25 S3 ’–CdS and ‘Cu2 Ge0.5 Sn0.5 S3 ’–CdS sections Using DTA and XRD results, vertical sections ‘Cu2 Ge0.75 Sn0.25 S3 ’–CdS (Fig. 6A) and ‘Cu2 Ge0.5 Sn0.5 S3 ’–CdS
Fig. 5. Change of the unit cell parameters for the samples of the Cu2 CdGeS4 –Cu2 CdSnS4 section.
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Fig. 6. Vertical sections ‘Cu2 Ge0.75 Sn0.25 S3 ’–CdS (A) and ‘Cu2 Ge0.5 Sn0.5 S3 ’–CdS (B) (1, L; 2, L + ; 3, L + ; 4, L +  + ; 5, L + ␥ + ; 6, L + ␦+ ; 7, ␦ + ; 8, ␥ + ␦ + ; 9,  + ␦ + ; 10, L + ␥; 11, L + ␣; 12, L + ␣ + ␥; 13, L + ␥ + ␦; 14, ␣; 15, ␣ + ␥; 16, ␣ + ␥ + ␦; 17, ␥ + ␦; 18,  + ␥ + ␦; 19, ; 20,  + ; 21,  + ␥ + ; 22,  + ␥).
(Fig. 6B) were constructed. These sections are similar, and were studied to determine the course of monovariant lines p1 U1 , p2 U2 , e1 E (Fig. 9) and the boundaries of the invariant processes that occur in the investigated system. The liquidus of the sections consists of four curves of the primary crystallization of -, -, ␥-, and ␣-solid solutions. The line ab belongs to the invariant plane of the peritectic process LU1 +  ⇔ ε + ␦ at 1187 K (Fig. 9). The region of the monovariant peritectic process L +  ⇔ borders on this plane. Point c separates the line ab into two parts. At the segment ac the invariant process ends with the exhaustion of the crystals of -solid solutions. At the segment cb the exhaustion of liquid is observed, and the alloys below this segment are three-phase ( + ␦ + ). The alloys below point c are two-phase (␦ + ). The horizontal line de forms by the crossing of these sections and the invariant plane of the peritectic process LU2 + ⇔ ␥ + ␦ at 1176 K (Fig. 9). The volumes of monovariant processes, peritectic L + ⇔ ␥ and eutectic L ⇔ ␦ + , converge to this line. Point f separates the line de into two parts with different end of the crystallization. In the alloys at the segment df the peritectic process ends with the exhaustion of -solid solutions; in the alloys at the segment fe it ends with the exhaustion of liquid, therefore below 1176 K, these alloys are three-phase. The alloys below point f are two-phase (␥ + ␦), because at this composition the invariant peritectic process ends with the exhaustion of both liquid and the crystals of -solid solutions. The quasi-ternary system undergoes a invariant eutectoid process ⇔  + ␥ + ␦ at 1125 K. Its existence is caused by the decomposition of Cu2 Cd3 GeS6 into Cu2 CdGeS4 and CdS at 1134 K in the quasi-binary system Cu2 GeS3 –CdS. The horizontal line gh forms by the crossing of these sections and the plane of the eutectoid decomposition. This line is the convergence of three-phase regions ␥ + ␦ + ,  + ␦ + and, in the section ‘Cu2 Ge0.75 Sn0.25 S3 ’–CdS, of the region of monovariant eutectoid process ⇔  + ␥. Below the segment gh, the alloys are three-phase ( + ␥ + ␦). An invariant eutectic process L ⇔ ␣ + ␥ + ␦ takes place in the system at 1117 K. The two sections cross the eutectic plane in the
segment kl. The regions of monovariant eutectic processes L ⇔ ␣ + ␥ and L ⇔ ␥ + ␦ converge to this horizontal. Below the segment kl, the alloys are three-phase (␣ + ␥ + ␦). The section solidus is formed by: line mn of the completion of the crystallization of ␣-solid solutions, line nk of the completion of monovariant eutectic process L ⇔ ␣ + ␥, line kl of the end of invariant eutectic process L ⇔ ␣ + ␥ + ␦, line lf of the completion of monovariant eutectic process L ⇔ ␥ + ␦, segment fe as the part of invariant peritectic plane L + ⇔ ␥ + ␦, curve ec that corresponds to the completion of monovariant eutectic process L ⇔ + ␦, segment cb as the part of invariant peritectic plane L +  ⇔ + ␦, curve bp (at the section ‘Cu2 Ge0.75 Sn0.25 S3 ’–CdS) that corresponds to the end of monovariant peritectic process L +  ⇔ with the exhaustion of the liquid, curves pr (at the section ‘Cu2 Ge0.75 Sn0.25 S3 ’–CdS) or br (at the section ‘Cu2 Ge0.5 Sn0.5 S3 ’–CdS) that correspond to the completion of the crystallization of -solid solutions. A representative heating and cooling DTA curves for the sample 70 ‘Cu2 Ge0.75 Sn0.25 S3 ’ + 30CdS is shown in Fig. 7. 4.5. The ‘Cu2 Ge0.25 Sn0.75 S3 ’–CdS section The vertical section ‘Cu2 Ge0.25 Sn0.75 S3 ’–CdS that was constructed using DTA and XRD results is presented in Fig. 8. The section was studied to determine the course of monovariant lines p3 U1 and e2 E (Fig. 9) and the boundaries of the invariant processes that take place in the investigated system. The liquidus consist of three curves of the primary crystallization of -, ␦-, and ␣-solid solutions. The horizontal line ab belongs to the invariant plane of the peritectic process LU1 +  ⇔ + ␦ at 1187 K (Fig. 9). This plane borders on the region of monovariant peritectic process L +  ⇔ ␦. Point c splits the segment ab into two parts. In the segment ac the process ends with the exhaustion of the crystals of -solid solutions, and the alloys below the segment ac are three-phase. In the other part the invariant process ends with the exhaustion of the liquid, therefore the alloys below the segment cb are three-phase ( + ␦ + ). The alloy below point c is two-phase (␦ + ).
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Fig. 7. DTA curves of the sample 70 ‘Cu2 Ge0.75 Sn0.25 S3 ’ + 30CdS during heating and cooling.
This section crosses the plane of invariant peritectic process LU2 + ⇔ ␥ + ␦ (Fig. 9) at 1176 K along the segment de. Above this plane one finds the region of monovariant eutectic process L ⇔ ␦ + . Point f splits the segment de into two parts with different end of the crystallization of alloys. The alloys with the composition falling onto the segment df end the peritectic process with the exhaustion of the crystals of -solid solutions, whereas the alloys of the fe segment end with the depletion of the liquid. Therefore these alloys are three-phase below 1176 K. The alloys below point f are two-phase (␥ + ␦), because at this composition the invariant peritectic process ends with the exhaustion of both the liquid and the crystals of -solid solutions. This section crosses the plane of invariant eutectoid decomposition ⇔  + ␥ + ␦, which takes place in the system at 1125 K, along the horizontal line gh. The three-phase regions ␥ + ␦ + and
Fig. 8. Vertical section ‘Cu2 Ge0.25 Sn0.75 S3 ’–CdS (1, L; 2, L + ; 3, L +  + ␦; 4, L + ␦; 5, L + ␦ + ; 6,  + ␦ + ; 7, ␦ + ; 8, L + ␥ + ␦; 9, ␥ + ␦ + ; 10, L + ␣; 11, L + ␣ + ␦; 12, ␣; 13, ␣ + ␦; 14, ␣ + ␥ + ␦; 15, ␥ + ␦; 16,  + ␥ + ␦; 17,  + ␦; 18, ).
Fig. 9. Liquidus surface projection of the Cu2 GeS3 –Cu2 SnS3 –CdS system.
 + ␦ + converge to this line. The alloys below the segment gh are three-phase ( + ␥ + ␦). The line kl is the crossing by this section of the invariant plane of the eutectic process L ⇔ ␣ + ␥ + ␦ at 1117 K. The volumes of monovariant eutectic processes L ⇔ ␣ + ␦ and L ⇔ ␥ + ␦ converge to this line. The alloys below the segment kl are three-phase (␣ + ␥ + ␦). 4.6. Liquidus surface projection of the quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS The liquidus surface projection of the Cu2 GeS3 –Cu2 SnS3 –CdS system onto the concentration triangle (Fig. 9) was constructed using the literature data on Cu2 GeS3 –CdS [8] and Cu2 SnS3 –CdS [10] phase diagrams, and own results of the investigation of the boundary system Cu2 GeS3 –Cu2 SnS3 and the six sections as described above. The liquidus surface consists of five fields of the primary crystallization of ␣-, -, ␥-, ␦- and -solid solutions. The field of -phase, as the component with the highest melting point, occupies the largest part of the concentration triangle. The fields of the primary crystallization are separated by seven monovariant lines and eight invariant points, of which three are ternary (two ternary peritectics and one ternary eutectic), and five are binary (three binary peritectics and two binary eutectics). The lines of the secondary crystallization of the binary peritectics p1 and p3 converge to the ternary peritectic point U1 . This point belongs to the plane corresponding to the process LU1 +  ⇔ + ␦ that takes place in the ternary system at 1187 K. The coordinates of the ternary peritectic point U1 are 25 mol.% CdS, 20 mol.% Cu2 GeS3 and 55 mol.% Cu2 SnS3 . The ternary peritectic point U2 is the convergence point of the monovariant lines of the secondary crystallization of the binary peritectic p2 and of the binary eutectic L ⇔ + ␦ (the line U1 U2 ). Point U2 belongs to the plane corresponding to the process LU2 + ⇔ ␥ + ␦ that takes place in the system at 1176 K. The coordinates of the ternary peritectic point U2 are 20 mol.% CdS, 25 mol.% Cu2 GeS3 and 55 mol.% Cu2 SnS3 . The lines of the secondary crystallization of the binary eutectics e1 , e2 and L ⇔ ␥ + ␦ (the line P2 E) converge to the ternary eutectic point E. This point belongs to the plane corresponding to the process LE ⇔ ␣ + ␥ + ␦ that takes place in the ternary system at 1117 K. The coordinates of the ternary invariant point E are 10 mol.% CdS, 30 mol.% Cu2 GeS3 and 60 mol.% Cu2 SnS3 .
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L.P. Marushko et al. / Journal of Alloys and Compounds 484 (2009) 147–153 Table 1 Nature and temperatures of mono- and invariant processes in the quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS.
The nature and the temperatures of mono- and invariant processes in the quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS are listed in Table 1. 4.7. Perspective view of the quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS The perspective view of the Cu2 GeS3 –Cu2 SnS3 –CdS phase diagram (Fig. 10) is represented as a trigonal prism. The vertical edges correspond to the compounds that form the system, points A, B and C correspond to the melting point of the system components, and prism faces represent the quasi-binary systems.
Fig. 10. Perspective view of the phase diagram of the quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS.
Five surfaces of the primary crystallization of the phases form the liquidus of the Cu2 GeS3 –Cu2 SnS3 –CdS system. The primary crystallization of -solid solution range of cadmium sulfide is represented by the surface Ap3 U1 p1 A; the crystallization of ␣-solid solution range of Cu2 GeS3 and Cu2 SnS3 is depicted as the surface Be1 Ee2 CB; that of ␥-solid solution range of the quaternary compound Cu2 CdGeS4 is shown as the surface p2 U2 Ee1 p2 ; the crystallization of ␦-solid solution range of the compound Cu2 CdSnS4 corresponds to the surface p3 e2 EU2 U1 p3 and, finally, the crystallization of -solid solution range of the quaternary compound Cu2 Cd3 GeS6 is represented by the surface p1 U1 U2 p2 p1 . Each of the three planes in the system corresponds to an invariant process. The plane U1 3 3 ␦2 U1 represents a four-phase invariant peritectic process LU1 + 3 ⇔ 3 + ␦2 . The beginning of the monovariant peritectic reaction L +  ⇔ corresponds to the surface p1 1 3 U1 p1 , the surface p1 1 3 U1 p1 denotes its end with the exhaustion of the crystals of -solid solutions, and the surface 1 1 3 3 1 presents the end of the peritectic process with the depletion of the liquid. The surface p3 U1 3 2 p3 corresponds to the beginning of the monovariant peritectic process L +  ⇔ ␦, its end with the exhaustion of the crystals of -solid solutions is shown as the surface p3 U1 ␦2 ␦1 p3 , the end of the process with the depletion of the liquid is given as the surface ␦1 ␦2 3 2 ␦1 , below which the alloys are two-phase and contain the crystals of - and ␦-solid solutions. The plane U2 ␥3 4 ␦3 U2 represents an invariant peritectic process LU2 + 4 ⇔ ␥3 + ␦3 . The monovariant peritectic process L + ⇔ ␥ starts as the surface p2 2 4 U2 p2 , and ends with the exhaustion of the crystals of -solid solutions at the surface p2 ␥1 ␥3 U2 p2 , or with the depletion of the liquid at the surface ␥1 2 4 ␥3 ␥1 , below which the alloys contain the crystals of ␥- and -solid solutions. The plane U2 ␥3 4 ␦3 U2 is the convergence point of the surfaces: 3 U1 U2 4 3 and ␦2 U1 U2 ␦3 ␦2 of the beginning of the monovariant eutectic process L ⇔ + ␦. The process ends at the surface ␦2 3 4 ␦3 ␦2 with the depletion of the liquid; the alloys below this surface are two-phase (␦- and -solid solutions). The plane ␣3 ␥6 ␦6 represents a eutectic process LE ⇔ ␣3 + ␥6 + ␦6 . The plane features the convergence of the surfaces ␣1 e1 E␣3 ␣1 and e1 ␥2 ␥6 Ee1 of the beginning of the monovariant eutectic process L + ␣ + ␥ which ends in the depletion of the liquid on the surface ␣1 ␥2 ␥6 ␣3 ␣1 below which the alloys are two-phase (␣- and ␥-solid solutions). The surfaces U2 ␥3 ␥6 EU2 and U2 ␦3 ␦6 EU2 characterize the beginning of the monovariant eutectic process L ⇔ ␥ + ␦ that ends at the surface ␥3 ␦3 ␦6 ␥6 ␥3 with the exhaustion of the liquid; below this surface the alloys are composed of the crystals of ␥- and ␦-solid solutions. The monovariant eutectic process L ⇔ ␣ + ␦ begins at the surfaces e2 ␣2 ␣3 Ee2 and ␦5 e2 E␦6 ␦5 ; it ends at the surface
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␦5 ␣2 ␣3 ␦6 ␦5 with the depletion of the liquid; the alloys contain the crystals of ␣- and ␦-solid solutions. The Cu2 GeS3 –CdS system features the nonvariant process of solid-state decomposition of the quaternary compound Cu2 Cd3 GeS6 (5 ⇔ 4 + ␥4 ). The presence of the component Cu2 SnS3 in the quasi-ternary system turns this decomposition process into a monovariant one. The surfaces 5 ␥4 ␥5 6 5 and 5 4 5 6 5 signify the beginning of this process in the alloys of the Cu2 GeS3 –Cu2 SnS3 –CdS system; the surface ␥4 4 5 ␥5 ␥4 characterizes its end with the exhaustion of the crystals of -solid solutions; the alloys are two-phase ( + ␥) below this surface. This plane conjoins two volumes: 4 ␥3 ␦3 ␦4 ␥5 6 , the volume of the co-existence of three phases ␥, ␦, (curve ␥3 ␥5 shows the change of the composition of ␥-solid solutions with the temperature decrease, curve ␦3 ␦4 – that of ␦-solid solutions, curve 4 6 – that of -solid solutions); and 3 ␦2 3 5 ␦4 6 —the volume of the co-existence of phases , ␦, (curve 3 5 depicts the change of the composition of -solid solutions as the temperature decreases, curve ␦2 ␦4 shows the change
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of the composition of ␦-solid solutions, curve 3 6 represents the compositions of -solid solutions). References [1] V.V. Philonenko, B.D. Nechyporuk, N.E. Novoseletskii, V.A. Yukhimchuk, Y.F. Lavoryk, Inorg. Mater. 27 (1991) 1166. [2] G.Y. Davydyuk, O.V. Parasyuk, S.A. Semenyuk, Y.E. Romanyuk, Inorg. Mater. 39 (2003) 1072. [3] G.Y. Davydyuk, I.D. Olekseyuk, O.V. Parasyuk, L.V. Piskach, S.A. Semenyuk, A.G. Kevshyn, V.I. Pekhnyo, Volyn State Univ. Bull. 1 (2005) 25. [4] E. Parté, K. Yvon, R.H. Deitch, Acta Crystallogr. B 25 (1969) 1164. [5] O.V. Parasyuk, Y.E. Romanyuk, I.D. Olekseyuk, J. Cryst. Growth 275 (2005) e159. [6] W. Schäfer, R. Nitshe, Mater. Res. Bull. 9 (1974) 645. [7] H. Matsushita, T. Ichikawa, A. Katsui, J. Mater. Sci. 40 (2005) 2003. [8] L.V. Piskach, O.V. Parasyuk, I.D. Olekseyuk, J. Alloys Compd. 299 (2000) 227. [9] G.Y. Davydyuk, O.V. Parasyuk, Y.E. Romanyuk, S.A. Semenyuk, V.I. Zaremba, L.V. Piskach, J.J. Kozioł, V.O. Halka, J. Alloys Compd. 339 (2002) 40. [10] I.D. Olekseyuk, L.V. Piskach, Inorg. Mater. 42 (1997) 331. [11] G.H. Moh, N. Mineral Abh. 128 (1976) 115. [12] L.P. Marushko, L.V. Piskach, Volyn State Univ. Bull. 4 (2006) 133.
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Quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS L.P. Marushko ∗ , L.V. Piskach, O.V. Parasyuk, I.A. Ivashchenko, I.D. Olekseyuk Department of General and Inorganic Chemistry, Volyn National University, Voli Ave 13, Lutsk 43025, Ukraine
a r t i c l e
i n f o
Article history: Received 10 April 2009 Received in revised form 27 April 2009 Accepted 27 April 2009 Available online 3 May 2009
a b s t r a c t Phase equilibria in the quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS were investigated by differential thermal analysis and XRD. Isothermal section of the system at 670 K, liquidus surface projection and the perspective views of the phase diagram were constructed. The boundaries of solid solution ranges of the system components and the intermediate phases were determined. © 2009 Elsevier B.V. All rights reserved.
Keywords: Semiconductors X-ray diffraction Thermal analysis
1. Introduction The quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS was investigated with a view to the formation of solid solution ranges of the quaternary compounds Cu2 CdGeS4 and Cu2 CdSnS4 which have semiconductor and optoelectronic properties [1–3]; this would allow one to obtain materials with a gradual modification of such properties. The AI 2 BII DIV X4 compounds that form in this system crystallize in two structures, orthorhombic wurtzite-stannite type ¯ (space group (s.g.) Pmn21 ) and tetragonal stannite type (s.g. I 42m) [4–6]. Noncentro-symmetrical structures are promising for the use in non-linear optics. The use of copper-containing phases Cu2 BII DIV X4 as solar cell materials is also feasible. Such materials must be semiconductors with the bandgap energy E = 1.1–1.5 eV. Cu2 BII DIV X4 compounds are isoelectronic analogs of CuInSe2 (by the substitution 2In → Cd + Ge) and possess the necessary properties. Considering p-type conductivity and the required bandgap values (e.g. 1.37 eV for Cu2 CdSnS4 [7]), the compounds are promising materials for the conversion of solar and polarized radiation in the heterojunctions with wide-gap BII X semiconductor with n-type conductivity. 2. Quasi-binary systems 2.1. The Cu2 GeS3 –CdS system The phase diagram of the Cu2 GeS3 –CdS system is presented in [8]. The system is quasi-binary, with the formation of two quater-
∗ Corresponding author. Tel.: +38 03322 49467; fax: +38 03322 41007. E-mail address: [email protected] (L.P. Marushko). 0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2009.04.128
nary compounds, Cu2 CdGeS4 and Cu2 Cd3 GeS6 . The former forms in the peritectic process L + Cu2 Cd3 GeS6 ⇔ Cu2 CdGeS4 at 1282 K and has a narrow homogeneity region. The eutectic of Cu2 GeS3 and Cu2 CdGeS4 has the coordinates of 16 mol.% CdS and 1229 K. The other quaternary phase, Cu2 Cd3 GeS6 , forms at 1329 K; its composition, as determined by the magnitude of endothermal effects, falls at 75 mol.% CdS. The phase is unstable and decomposes at 1134 K. The solid solution ranges of the system components do not exceed 2 mol.%. The Cu2 CdGeS4 compound crystallizes in the wurtzite–stannite structure type (s.g. Pmn21 ) with unit cell parameters a = 0.77024, b = 0.65486, c = 0.62928 nm [5]. The bandgap energy of Cu2 CdGeS4 equals 2.05 eV at 290 K, with the hole conduction [9]. The thermoEMF coefficient reaches 1800 V/K; combined with low thermal conductivity, the compound may be promising for thermoelectronic applications [2].
2.2. The Cu2 SnS3 –CdS system The quasi-binary system Cu2 SnS3 –CdS was investigated in [10]. The quaternary compound Cu2 CdSnS4 that forms in the system melts incongruently at 1178 K. The eutectic point of Cu2 CdSnS4 and Cu2 SnS3 has the coordinates of 15 mol.% CdS and 1126 K. The solid solution range of Cu2 SnS3 extends to 10 mol.% CdS at 1126 K, and to 8 mol.% CdS at 820 K. The solid solution range of CdS includes 6 mol.% Cu2 SnS3 at 1178 K and decreases with lower temperature. The quaternary compound Cu2 CdSnS4 melts at 1187 K according to [11], and at 1199 K according to [7]. ¯ Cu2 CdSnS4 crystallizes in the stannite structure type (s.g. I 42m) with unit cell parameters a = 0.5586, c = 1.0834 nm [6]. The bandgap energy of Cu2 CdSnS4 equals 1.4 eV at 290 K. This compound is also characterized by p-type conductivity [3].
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L.P. Marushko et al. / Journal of Alloys and Compounds 484 (2009) 147–153 stage the ampoules were heated in oxygen-gas burner flame to complete bonding of elementary sulfur. The second stage was performed in a shaft-type furnace. The alloys were heated at the rate of 50 K/h to the maximum temperature set at 50–100 K above the melting points of the components. After the exposure to the maximum temperature for 2–3 h the alloys were slowly cooled at the rate of 10 K/h to 670 K. The samples were annealed at this temperature for 500 h, followed by quenching into cold water. The synthesis resulted in compact dark-grey ingots. Obtained alloys were investigated by differential thermal analysis (PaulikPaulik-Erdey derivatograph, Pt/Pt-Rh thermocouple) and XRD (DRON 4–13 diffractometer, Cu K␣ radiation, Ni filter, /2 scanning in the angle range 10◦ ≤ 2 ≤90◦ , scan step of 0.05◦ , scan time 1 s). The computation of unit cell parameters of the studied samples was performed using PDWin-2 software package.
4. Results 4.1. Isothermal section of the Cu2 GeS3 –Cu2 SnS3 –CdS system
Fig. 1. Phase diagram of the Cu2 GeS3 –Cu2 SnS3 system (1, L; 2, L + ␣; 3, ␣).
2.3. The Cu2 GeS3 –Cu2 SnS3 system The Cu2 GeS3 –Cu2 SnS3 system was investigated by us earlier [12]. The system components form a continuous solid solution series. The phase diagram belongs to Type III of Roozeboom classification. During the construction of the liquidus surface projection of the quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS we refined the phase diagram of the Cu2 GeS3 –Cu2 SnS3 system (Fig. 1). Namely, the minimum coordinates are ∼66 mol.% Cu2 SnS3 and 1125 K.
From the results of X-ray phase analysis of the alloys of the Cu2 GeS3 –Cu2 SnS3 –CdS system, the isothermal section at 670 K was constructed shown in Fig. 2. The existence of four single-phase regions was established in the system at this temperature. They are: the continuous solid solution series of Cu2 GeS3 and Cu2 SnS3 (␣-solid solutions); solid solutions of the quaternary compounds stretched along the Cu2 CdGeS4 –Cu2 CdSnS4 section: ␥-solid solution range of Cu2 CdGeS4 with the orthorhombic structure which extends to 9 mol.% Cu2 CdSnS4 , and ␦-solid solution range of Cu2 CdSnS4 with the stannite structure which extends to 14 mol.% Cu2 CdGeS4 ; and -solid solution range of CdS with the wurtzite structure. Another -solid solutions range of Cu2 Cd3 GeS6 is absent from the isothermal section at 670 K as -solid solutions undergo eutectoid decomposition below 1125 K. Additionally, five two-phase regions and two three-phase regions exist in the system at the annealing temperature. 4.2. The Cu2 Cd3 GeS6 –Cu2 CdSnS4 section
3. Experimental The investigation of phase equilibria in the Cu2 GeS3 –Cu2 SnS3 –CdS system was performed using 88 alloys, their compositions are presented in Fig. 2. The alloys were synthesized from high-purity elements (at least 99.99 wt.% of the principal element). Calculated amounts were placed into quartz ampoules that were evacuated to 10−1 Pa and soldered. The synthesis was performed in two stages. At the first
The vertical section Cu2 Cd3 GeS6 –Cu2 CdSnS4 is presented in Fig. 3. The section was studied to determine the boundaries of the invariant processes, peritectic LU1 +  ⇔ ␦ + (Fig. 9) and eutectoid ⇔  + ␥ + ␦, that occur in the system. The section liquidus consists of the curve of the primary crystallization of -solid solutions. Cu2 CdSnS4 forms in a peritectic process at 1193 K. The section crosses the plane of the invariant peritectic process LU1 +  ⇔ ␦ + at 1187 K. The curve ab coincides with the polytherm of the solubility of -solid solutions, therefore single-phase field borders on the three-phase field L +  + . The alloys below 1187 K are three-phase ( + ␦ + ) as the peritectic process leads to the depletion of the liquid. The alloys of the section undergo a monovariant eutectoid process ⇔  + ␥ + ␦ at 1125 K. Its existence is caused by the decomposition of Cu2 Cd3 GeS6 . The composition of -solid solutions during the monovariant eutectoid process follows the curve cd, therefore the single-phase region of -solid solutions borders on the three-phase field  + ␥ + . The majority of the alloys below 1125 K are three-project and contain the crystals of -, ␥- and ␦solid solutions. 4.3. The Cu2 CdGeS4 –Cu2 CdSnS4 section
Fig. 2. Isothermal section of the Cu2 GeS3 –Cu2 SnS3 –CdS system at 670 K, phase and chemical composition of alloys.
The vertical section Cu2 CdGeS4 –Cu2 CdSnS4 was constructed from DTA and XRD results (Fig. 4). The section was studied to determine the exact position of the monovariant line p1 U1 (Fig. 9), the solid solubility ranges of the quaternary compounds, and the boundaries of the invariant peritectic processes that occur in the system.
L.P. Marushko et al. / Journal of Alloys and Compounds 484 (2009) 147–153
Fig. 3. Vertical section Cu2 Cd3 GeS6 –Cu2 CdSnS4 (1, L; 2, L + ; 3, L +  + ; 4, L +  + ␦; 5, ; 6,  + ␦ + ; 7,  + ␦; 8,  + ␥ + ; 9,  + ␥; 10,  + ␥ + ␦; 11, ␦).
The section liquidus is represented by the primary crystallization of -solid solutions (curve ab) and -solid solutions (curve bc). The section crosses the plane of the invariant peritectic process LU1 +  ⇔ ␦ + (Fig. 9) at 1187 K forming the horizontal line de. The regions of the co-existence of three phase L +  + and L +  + ␦ converge to this line. Below the line de we find the region of the monovariant eutectic process L ⇔ ␦ + ; this, together with the region of the monovariant peritectic process L + ⇔ ␥, converge to the segment fg. This horizontal line belongs to the plane of the invariant peritectic process LU2 + ⇔ ␥ + ␦ (Fig. 9) that takes place at 1176 K. The segment fg coincides with the connect-
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Fig. 4. Vertical section Cu2 CdGeS4 –Cu2 CdSnS4 (1, L; 2, L + ; 3, L + ; 4, L +  + ; 5, L +  + ␦; 6, L + ␥ + ; 7, L + ␦ + ; 8, L + ␦; 9, ␥; 10, ␦; 11, ␥ + ␦).
ing line of this plane, therefore the section alloys are two-phase (␥ + ␦) below 1176 K. The extent of ␥-solid solutions at this temperature is 11 mol.% Cu2 CdSnS4 , that of ␦-solid solutions is 16 mol.% Cu2 CdGeS4 . The solid solution ranges vary little with temperature, and equal 9 mol.% for ␥-solid solutions and 14 mol.% for ␦-solid solutions at 670 K. The ranges of solid solutions were determined from the change of unit cell parameters of alloys (Fig. 5). 4.4. The ‘Cu2 Ge0.75 Sn0.25 S3 ’–CdS and ‘Cu2 Ge0.5 Sn0.5 S3 ’–CdS sections Using DTA and XRD results, vertical sections ‘Cu2 Ge0.75 Sn0.25 S3 ’–CdS (Fig. 6A) and ‘Cu2 Ge0.5 Sn0.5 S3 ’–CdS
Fig. 5. Change of the unit cell parameters for the samples of the Cu2 CdGeS4 –Cu2 CdSnS4 section.
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Fig. 6. Vertical sections ‘Cu2 Ge0.75 Sn0.25 S3 ’–CdS (A) and ‘Cu2 Ge0.5 Sn0.5 S3 ’–CdS (B) (1, L; 2, L + ; 3, L + ; 4, L +  + ; 5, L + ␥ + ; 6, L + ␦+ ; 7, ␦ + ; 8, ␥ + ␦ + ; 9,  + ␦ + ; 10, L + ␥; 11, L + ␣; 12, L + ␣ + ␥; 13, L + ␥ + ␦; 14, ␣; 15, ␣ + ␥; 16, ␣ + ␥ + ␦; 17, ␥ + ␦; 18,  + ␥ + ␦; 19, ; 20,  + ; 21,  + ␥ + ; 22,  + ␥).
(Fig. 6B) were constructed. These sections are similar, and were studied to determine the course of monovariant lines p1 U1 , p2 U2 , e1 E (Fig. 9) and the boundaries of the invariant processes that occur in the investigated system. The liquidus of the sections consists of four curves of the primary crystallization of -, -, ␥-, and ␣-solid solutions. The line ab belongs to the invariant plane of the peritectic process LU1 +  ⇔ ε + ␦ at 1187 K (Fig. 9). The region of the monovariant peritectic process L +  ⇔ borders on this plane. Point c separates the line ab into two parts. At the segment ac the invariant process ends with the exhaustion of the crystals of -solid solutions. At the segment cb the exhaustion of liquid is observed, and the alloys below this segment are three-phase ( + ␦ + ). The alloys below point c are two-phase (␦ + ). The horizontal line de forms by the crossing of these sections and the invariant plane of the peritectic process LU2 + ⇔ ␥ + ␦ at 1176 K (Fig. 9). The volumes of monovariant processes, peritectic L + ⇔ ␥ and eutectic L ⇔ ␦ + , converge to this line. Point f separates the line de into two parts with different end of the crystallization. In the alloys at the segment df the peritectic process ends with the exhaustion of -solid solutions; in the alloys at the segment fe it ends with the exhaustion of liquid, therefore below 1176 K, these alloys are three-phase. The alloys below point f are two-phase (␥ + ␦), because at this composition the invariant peritectic process ends with the exhaustion of both liquid and the crystals of -solid solutions. The quasi-ternary system undergoes a invariant eutectoid process ⇔  + ␥ + ␦ at 1125 K. Its existence is caused by the decomposition of Cu2 Cd3 GeS6 into Cu2 CdGeS4 and CdS at 1134 K in the quasi-binary system Cu2 GeS3 –CdS. The horizontal line gh forms by the crossing of these sections and the plane of the eutectoid decomposition. This line is the convergence of three-phase regions ␥ + ␦ + ,  + ␦ + and, in the section ‘Cu2 Ge0.75 Sn0.25 S3 ’–CdS, of the region of monovariant eutectoid process ⇔  + ␥. Below the segment gh, the alloys are three-phase ( + ␥ + ␦). An invariant eutectic process L ⇔ ␣ + ␥ + ␦ takes place in the system at 1117 K. The two sections cross the eutectic plane in the
segment kl. The regions of monovariant eutectic processes L ⇔ ␣ + ␥ and L ⇔ ␥ + ␦ converge to this horizontal. Below the segment kl, the alloys are three-phase (␣ + ␥ + ␦). The section solidus is formed by: line mn of the completion of the crystallization of ␣-solid solutions, line nk of the completion of monovariant eutectic process L ⇔ ␣ + ␥, line kl of the end of invariant eutectic process L ⇔ ␣ + ␥ + ␦, line lf of the completion of monovariant eutectic process L ⇔ ␥ + ␦, segment fe as the part of invariant peritectic plane L + ⇔ ␥ + ␦, curve ec that corresponds to the completion of monovariant eutectic process L ⇔ + ␦, segment cb as the part of invariant peritectic plane L +  ⇔ + ␦, curve bp (at the section ‘Cu2 Ge0.75 Sn0.25 S3 ’–CdS) that corresponds to the end of monovariant peritectic process L +  ⇔ with the exhaustion of the liquid, curves pr (at the section ‘Cu2 Ge0.75 Sn0.25 S3 ’–CdS) or br (at the section ‘Cu2 Ge0.5 Sn0.5 S3 ’–CdS) that correspond to the completion of the crystallization of -solid solutions. A representative heating and cooling DTA curves for the sample 70 ‘Cu2 Ge0.75 Sn0.25 S3 ’ + 30CdS is shown in Fig. 7. 4.5. The ‘Cu2 Ge0.25 Sn0.75 S3 ’–CdS section The vertical section ‘Cu2 Ge0.25 Sn0.75 S3 ’–CdS that was constructed using DTA and XRD results is presented in Fig. 8. The section was studied to determine the course of monovariant lines p3 U1 and e2 E (Fig. 9) and the boundaries of the invariant processes that take place in the investigated system. The liquidus consist of three curves of the primary crystallization of -, ␦-, and ␣-solid solutions. The horizontal line ab belongs to the invariant plane of the peritectic process LU1 +  ⇔ + ␦ at 1187 K (Fig. 9). This plane borders on the region of monovariant peritectic process L +  ⇔ ␦. Point c splits the segment ab into two parts. In the segment ac the process ends with the exhaustion of the crystals of -solid solutions, and the alloys below the segment ac are three-phase. In the other part the invariant process ends with the exhaustion of the liquid, therefore the alloys below the segment cb are three-phase ( + ␦ + ). The alloy below point c is two-phase (␦ + ).
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Fig. 7. DTA curves of the sample 70 ‘Cu2 Ge0.75 Sn0.25 S3 ’ + 30CdS during heating and cooling.
This section crosses the plane of invariant peritectic process LU2 + ⇔ ␥ + ␦ (Fig. 9) at 1176 K along the segment de. Above this plane one finds the region of monovariant eutectic process L ⇔ ␦ + . Point f splits the segment de into two parts with different end of the crystallization of alloys. The alloys with the composition falling onto the segment df end the peritectic process with the exhaustion of the crystals of -solid solutions, whereas the alloys of the fe segment end with the depletion of the liquid. Therefore these alloys are three-phase below 1176 K. The alloys below point f are two-phase (␥ + ␦), because at this composition the invariant peritectic process ends with the exhaustion of both the liquid and the crystals of -solid solutions. This section crosses the plane of invariant eutectoid decomposition ⇔  + ␥ + ␦, which takes place in the system at 1125 K, along the horizontal line gh. The three-phase regions ␥ + ␦ + and
Fig. 8. Vertical section ‘Cu2 Ge0.25 Sn0.75 S3 ’–CdS (1, L; 2, L + ; 3, L +  + ␦; 4, L + ␦; 5, L + ␦ + ; 6,  + ␦ + ; 7, ␦ + ; 8, L + ␥ + ␦; 9, ␥ + ␦ + ; 10, L + ␣; 11, L + ␣ + ␦; 12, ␣; 13, ␣ + ␦; 14, ␣ + ␥ + ␦; 15, ␥ + ␦; 16,  + ␥ + ␦; 17,  + ␦; 18, ).
Fig. 9. Liquidus surface projection of the Cu2 GeS3 –Cu2 SnS3 –CdS system.
 + ␦ + converge to this line. The alloys below the segment gh are three-phase ( + ␥ + ␦). The line kl is the crossing by this section of the invariant plane of the eutectic process L ⇔ ␣ + ␥ + ␦ at 1117 K. The volumes of monovariant eutectic processes L ⇔ ␣ + ␦ and L ⇔ ␥ + ␦ converge to this line. The alloys below the segment kl are three-phase (␣ + ␥ + ␦). 4.6. Liquidus surface projection of the quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS The liquidus surface projection of the Cu2 GeS3 –Cu2 SnS3 –CdS system onto the concentration triangle (Fig. 9) was constructed using the literature data on Cu2 GeS3 –CdS [8] and Cu2 SnS3 –CdS [10] phase diagrams, and own results of the investigation of the boundary system Cu2 GeS3 –Cu2 SnS3 and the six sections as described above. The liquidus surface consists of five fields of the primary crystallization of ␣-, -, ␥-, ␦- and -solid solutions. The field of -phase, as the component with the highest melting point, occupies the largest part of the concentration triangle. The fields of the primary crystallization are separated by seven monovariant lines and eight invariant points, of which three are ternary (two ternary peritectics and one ternary eutectic), and five are binary (three binary peritectics and two binary eutectics). The lines of the secondary crystallization of the binary peritectics p1 and p3 converge to the ternary peritectic point U1 . This point belongs to the plane corresponding to the process LU1 +  ⇔ + ␦ that takes place in the ternary system at 1187 K. The coordinates of the ternary peritectic point U1 are 25 mol.% CdS, 20 mol.% Cu2 GeS3 and 55 mol.% Cu2 SnS3 . The ternary peritectic point U2 is the convergence point of the monovariant lines of the secondary crystallization of the binary peritectic p2 and of the binary eutectic L ⇔ + ␦ (the line U1 U2 ). Point U2 belongs to the plane corresponding to the process LU2 + ⇔ ␥ + ␦ that takes place in the system at 1176 K. The coordinates of the ternary peritectic point U2 are 20 mol.% CdS, 25 mol.% Cu2 GeS3 and 55 mol.% Cu2 SnS3 . The lines of the secondary crystallization of the binary eutectics e1 , e2 and L ⇔ ␥ + ␦ (the line P2 E) converge to the ternary eutectic point E. This point belongs to the plane corresponding to the process LE ⇔ ␣ + ␥ + ␦ that takes place in the ternary system at 1117 K. The coordinates of the ternary invariant point E are 10 mol.% CdS, 30 mol.% Cu2 GeS3 and 60 mol.% Cu2 SnS3 .
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L.P. Marushko et al. / Journal of Alloys and Compounds 484 (2009) 147–153 Table 1 Nature and temperatures of mono- and invariant processes in the quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS.
The nature and the temperatures of mono- and invariant processes in the quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS are listed in Table 1. 4.7. Perspective view of the quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS The perspective view of the Cu2 GeS3 –Cu2 SnS3 –CdS phase diagram (Fig. 10) is represented as a trigonal prism. The vertical edges correspond to the compounds that form the system, points A, B and C correspond to the melting point of the system components, and prism faces represent the quasi-binary systems.
Fig. 10. Perspective view of the phase diagram of the quasi-ternary system Cu2 GeS3 –Cu2 SnS3 –CdS.
Five surfaces of the primary crystallization of the phases form the liquidus of the Cu2 GeS3 –Cu2 SnS3 –CdS system. The primary crystallization of -solid solution range of cadmium sulfide is represented by the surface Ap3 U1 p1 A; the crystallization of ␣-solid solution range of Cu2 GeS3 and Cu2 SnS3 is depicted as the surface Be1 Ee2 CB; that of ␥-solid solution range of the quaternary compound Cu2 CdGeS4 is shown as the surface p2 U2 Ee1 p2 ; the crystallization of ␦-solid solution range of the compound Cu2 CdSnS4 corresponds to the surface p3 e2 EU2 U1 p3 and, finally, the crystallization of -solid solution range of the quaternary compound Cu2 Cd3 GeS6 is represented by the surface p1 U1 U2 p2 p1 . Each of the three planes in the system corresponds to an invariant process. The plane U1 3 3 ␦2 U1 represents a four-phase invariant peritectic process LU1 + 3 ⇔ 3 + ␦2 . The beginning of the monovariant peritectic reaction L +  ⇔ corresponds to the surface p1 1 3 U1 p1 , the surface p1 1 3 U1 p1 denotes its end with the exhaustion of the crystals of -solid solutions, and the surface 1 1 3 3 1 presents the end of the peritectic process with the depletion of the liquid. The surface p3 U1 3 2 p3 corresponds to the beginning of the monovariant peritectic process L +  ⇔ ␦, its end with the exhaustion of the crystals of -solid solutions is shown as the surface p3 U1 ␦2 ␦1 p3 , the end of the process with the depletion of the liquid is given as the surface ␦1 ␦2 3 2 ␦1 , below which the alloys are two-phase and contain the crystals of - and ␦-solid solutions. The plane U2 ␥3 4 ␦3 U2 represents an invariant peritectic process LU2 + 4 ⇔ ␥3 + ␦3 . The monovariant peritectic process L + ⇔ ␥ starts as the surface p2 2 4 U2 p2 , and ends with the exhaustion of the crystals of -solid solutions at the surface p2 ␥1 ␥3 U2 p2 , or with the depletion of the liquid at the surface ␥1 2 4 ␥3 ␥1 , below which the alloys contain the crystals of ␥- and -solid solutions. The plane U2 ␥3 4 ␦3 U2 is the convergence point of the surfaces: 3 U1 U2 4 3 and ␦2 U1 U2 ␦3 ␦2 of the beginning of the monovariant eutectic process L ⇔ + ␦. The process ends at the surface ␦2 3 4 ␦3 ␦2 with the depletion of the liquid; the alloys below this surface are two-phase (␦- and -solid solutions). The plane ␣3 ␥6 ␦6 represents a eutectic process LE ⇔ ␣3 + ␥6 + ␦6 . The plane features the convergence of the surfaces ␣1 e1 E␣3 ␣1 and e1 ␥2 ␥6 Ee1 of the beginning of the monovariant eutectic process L + ␣ + ␥ which ends in the depletion of the liquid on the surface ␣1 ␥2 ␥6 ␣3 ␣1 below which the alloys are two-phase (␣- and ␥-solid solutions). The surfaces U2 ␥3 ␥6 EU2 and U2 ␦3 ␦6 EU2 characterize the beginning of the monovariant eutectic process L ⇔ ␥ + ␦ that ends at the surface ␥3 ␦3 ␦6 ␥6 ␥3 with the exhaustion of the liquid; below this surface the alloys are composed of the crystals of ␥- and ␦-solid solutions. The monovariant eutectic process L ⇔ ␣ + ␦ begins at the surfaces e2 ␣2 ␣3 Ee2 and ␦5 e2 E␦6 ␦5 ; it ends at the surface
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␦5 ␣2 ␣3 ␦6 ␦5 with the depletion of the liquid; the alloys contain the crystals of ␣- and ␦-solid solutions. The Cu2 GeS3 –CdS system features the nonvariant process of solid-state decomposition of the quaternary compound Cu2 Cd3 GeS6 (5 ⇔ 4 + ␥4 ). The presence of the component Cu2 SnS3 in the quasi-ternary system turns this decomposition process into a monovariant one. The surfaces 5 ␥4 ␥5 6 5 and 5 4 5 6 5 signify the beginning of this process in the alloys of the Cu2 GeS3 –Cu2 SnS3 –CdS system; the surface ␥4 4 5 ␥5 ␥4 characterizes its end with the exhaustion of the crystals of -solid solutions; the alloys are two-phase ( + ␥) below this surface. This plane conjoins two volumes: 4 ␥3 ␦3 ␦4 ␥5 6 , the volume of the co-existence of three phases ␥, ␦, (curve ␥3 ␥5 shows the change of the composition of ␥-solid solutions with the temperature decrease, curve ␦3 ␦4 – that of ␦-solid solutions, curve 4 6 – that of -solid solutions); and 3 ␦2 3 5 ␦4 6 —the volume of the co-existence of phases , ␦, (curve 3 5 depicts the change of the composition of -solid solutions as the temperature decreases, curve ␦2 ␦4 shows the change
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of the composition of ␦-solid solutions, curve 3 6 represents the compositions of -solid solutions). References [1] V.V. Philonenko, B.D. Nechyporuk, N.E. Novoseletskii, V.A. Yukhimchuk, Y.F. Lavoryk, Inorg. Mater. 27 (1991) 1166. [2] G.Y. Davydyuk, O.V. Parasyuk, S.A. Semenyuk, Y.E. Romanyuk, Inorg. Mater. 39 (2003) 1072. [3] G.Y. Davydyuk, I.D. Olekseyuk, O.V. Parasyuk, L.V. Piskach, S.A. Semenyuk, A.G. Kevshyn, V.I. Pekhnyo, Volyn State Univ. Bull. 1 (2005) 25. [4] E. Parté, K. Yvon, R.H. Deitch, Acta Crystallogr. B 25 (1969) 1164. [5] O.V. Parasyuk, Y.E. Romanyuk, I.D. Olekseyuk, J. Cryst. Growth 275 (2005) e159. [6] W. Schäfer, R. Nitshe, Mater. Res. Bull. 9 (1974) 645. [7] H. Matsushita, T. Ichikawa, A. Katsui, J. Mater. Sci. 40 (2005) 2003. [8] L.V. Piskach, O.V. Parasyuk, I.D. Olekseyuk, J. Alloys Compd. 299 (2000) 227. [9] G.Y. Davydyuk, O.V. Parasyuk, Y.E. Romanyuk, S.A. Semenyuk, V.I. Zaremba, L.V. Piskach, J.J. Kozioł, V.O. Halka, J. Alloys Compd. 339 (2002) 40. [10] I.D. Olekseyuk, L.V. Piskach, Inorg. Mater. 42 (1997) 331. [11] G.H. Moh, N. Mineral Abh. 128 (1976) 115. [12] L.P. Marushko, L.V. Piskach, Volyn State Univ. Bull. 4 (2006) 133.