Journal of Alloys and Compounds 610 (2014) 161–168

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Journal of Alloys and Compounds

journal homepage: www.elsevier .com/locate / ja lcom

Experimental investigation and thermodynamic predictionof the Ag–Ge–Sb phase diagram

http://dx.doi.org/10.1016/j.jallcom.2014.04.2080925-8388/� 2014 Published by Elsevier B.V.

⇑ Corresponding author. Tel.: +381 653005603.E-mail address: milena.premovic@gmail.com (M. Premovic).

Milena Premovic a,⇑, Dragan Manasijevic b, Duško Minic a, Dragana Zivkovic b

a University in Priština, Faculty of Technical Science, Kos. Mitrovica, Serbiab University of Belgrade, Technical Faculty, Bor, Serbia

a r t i c l e i n f o a b s t r a c t

Article history:Received 11 March 2014Received in revised form 24 April 2014Accepted 28 April 2014Available online 9 May 2014

Keywords:Ag–Ge–Sb systemPhase diagramDTAXRDSEM–EDS

Phase diagram of the Ag–Ge–Sb ternary system has been investigated experimentally and extrapolatedusing optimized thermodynamic parameters for the constitutive binary systems. Experimental resultsobtained using differential thermal analysis (DTA), scanning electron microscopy (SEM) with energy dis-persive spectrometry (EDS), and X-ray powder diffraction (XRD) methods were compared with predictedphase equilibria.

Identification of coexisting phases in the chosen as-cast samples and samples annealed at 400 �C wasperformed using SEM–EDS and XRD methods. Liquidus temperatures for selected samples with overallcompositions along three vertical sections Ag–Ge0.5Sb0.5, Ge–Ag0.5Sb0.5 and Sb–Ge0.5Ag0.5 were measuredby DTA. Ternary eutectic reaction was experimentally determined by means of applied experimentaltechniques.

� 2014 Published by Elsevier B.V.

1. Introduction

It is well known that silver and silver alloys represent excellentheat and electricity conductors. For example, alloys of Ag–Sbsystem are widely used in electronic industry [1–3]. Also,germanium based alloys are extensively studied because of theirsemiconducting properties and applications in the electronicindustry [4–7]. In addition to these applications, special attentionis given to materials which contain Ge, due to the large applicationin the modern technology for making optical discs, DVD, Blue-Raydiscs, flash memories [8,9]. Also, Sb-rich alloys of Ge, Ag, In, Gaare important for development of phase change memorymaterials [10].

The aim of this study is complementary experimental and com-putational investigation of phase transitions and microstructure ofthe alloys in ternary Ag–Ge–Sb system which has not yet beenstudied from this point of view in literature. Hereby, selected alloysof the Ag–Ge–Sb ternary system were prepared and studied using acombination of different experimental techniques (DTA, SEM–EDS,XRD). Experimentally obtained results were compared with pre-dicted phase equilibria.

2. Experimental procedure

All samples with total masses of about 3 g were prepared from Ge, Sb and Agshots of 99.99% purity in an induction furnace under high purity argon atmosphere.After melting, the samples were put into quartz glass ampoules, sealed under vac-uum, annealed at 400 �C for two weeks and quenched into ice water. Additionally,four as-cast samples were prepared for microstructure investigation.

The compositions of coexisting phases were determined using JEOL JSM-6460scanning electron microscope with energy dispersive spectrometry, EDS (OxfordInstruments).

Powder XRD data for phase identification of samples were recorded on a D2PHASER (Bruker) powder diffractometer equipped with a dynamic scintillationdetector and ceramic X-ray Cu tube (KFL-Cu-2 K) in a 2h range from 5� to 75� witha step size of 0.02�. The patterns were analyzed using the Topas 4.2 software, ICDDdatabases PDF2 (2013).

Phase transition temperatures were determined by DTA method. The DTA mea-surements were performed on a SDT Q600 (TA instruments). Alumina crucibleswere used and measurements were performed under flowing argon atmosphere.Samples weighing between 20 and 30 mg were investigated at heating rate of5 �C/min. The sample masses and heating rates were determined by analysis ofone sample at different testing conditions. The reference material was empty alu-mina crucible. The overall uncertainty of the determined phase transformation tem-peratures was estimated to be ±1 �C.

3. Literature data

To the best of our knowledge, there are no published dataregarding the phase equilibria and thermodynamics of the ternaryAg–Ge–Sb system. Boundary binary systems have been investi-gated extensively.

162 M. Premovic et al. / Journal of Alloys and Compounds 610 (2014) 161–168

3.1. The Ag–Ge binary system

The Ag–Ge binary system is a simple eutectic system, whichconsists of three condensed phases: liquid phase, (Ag) and (Ge)solid solutions. Temperature and composition of eutectic reactionand the position of the liquidus line have been investigated byBriggs et al. [11], Maucher [12] and Predel and Bamlstahl [13]using thermal analysis.

Owen and Rowlands [14] determined solubility of Ge in the (Ag)phase below the eutectic temperature using X-ray powder method.Also, Pollock [15] reported the composition of the (Ag) phase at thetemperature about 300 K from thermoelectric measurements.

The enthalpies of mixing of liquid Ag–Ge alloys were measuredby Castanet et al. [16,17] at 1280 K and Batalin et al. [18] at 1430 K.Activities of Ag in the liquid Ag–Ge alloys were determined byBatalin et al. [18], Eremenko et al. [19], Martin-Garin et al. [20]and Oktay [21].

This system was first thermodynamically optimized byChevalier [22]. In order to achieve the thermodynamic compatibil-ity of the database in the multi-component systems, the thermody-namic parameters of different phases in the Ag–Ge binary systemwere evaluated by Wang et al. [23].

3.2. The Ge–Sb binary system

The Ge–Sb binary system is an eutectic system. Phase equilibriaof this system have been investigated by several authors [24–29].

A very small solubility of antimony in germanium was deter-mined by Zhurkin et al. [26], Trumbore [30], Trumbore et al. [31],Akopyan and Abdullayev [32], and Glazov and Abdullyev [33].

The enthalpies of mixing in liquid Ge–Sb alloys were deter-mined by Predel and Stein [34] and Alfer et al. [35]. Activities Ge

Table 1The optimized binary parameters used in this study.

Phase and thermodynamic model Thermodynamic

Liquid (Ag, Ge, Sb) 0LLiquidAg;Sb ¼ �964:4

1LLiquidAg;Sb ¼ �2148

2LLiquidAg;Sb ¼ �9992

0LLiquidAg;Ge ¼ 7636:8

1LLiquidAg;Ge ¼ �14500

2LLiquidAg;Ge ¼ �7029

0LLiquidGe;Sb ¼ þ3289

Fcc_A1 (Ag, Ge, Sb)1(Va)1 0LFcc A1Ag;Sb:Va ¼ �301

1LFcc A1Ag;Sb:Va ¼ 8714

0LFcc A1Ag;Ge:Va ¼ 5696

1LFcc A1Ag;Ge:Va ¼ �202

Hcp_A3 (Ag, Sb)1(Va)0.5 0LHcp A3Ag;Sb:Va ¼ �241

1LHcp A3Ag;Sb:Va ¼ �234

AgSb_ortho (Ag, Sb)3(Ag,Sb)1 0LAgSb orthoAg:Ag ¼ GSe

Ag

0LAgSb orthoSb:Sb ¼ GSe

Sb

0LAgSb orthoAg:Sb ¼ 0:7

0LAgSb orthoSb:Ag ¼ 0:7

0LAgSb orthoAg:Ag;Sb ¼ �5

0LAgSb orthoAg;Sb:Sb ¼ 104

0LAgSb orthoAg;Sb:Ag ¼ 0

0LAgSb otrhoSb:Ag;Sb ¼ 0

Diamond_A4 (Ge, Sb) 0LDiamond A4Ge;Sb ¼ þ7

Rhombo_A7 (Ge, Sb) 0LR hom bo A7Ge;Sb ¼ þ

and Sb in the liquid state at 1073, 1173, 1273 K were investigatedby Kostov et al. [6].

The binary Ge–Sb system was initially thermodynamically opti-mized by Chevalier [36] based on experimentally determinedphase diagram by Olesinski et al. [37,38]. Later, it was re-optimizedby Liu et al. [39] using new experimental results by Nasir et al. [40].

3.3. The Ag–Sb binary system

The Ag–Sb system exhibits five phases: liquid phase, (Ag) and(Sb) solid solutions, f (Ag9Sb) and e (Ag3Sb) intermetallic phases.

The liquidus is constructed by Hansen and Anderko [41] basedon previous experimental results published in literature [42–45].Okamoto [46] reported two intermediate phases: f (Ag9Sb) and e(Ag3Sb) that form by peritectic reactions at 702.5 and 562 �C, andthe eutectic reaction at 485 �C. Feschotte et al. [47] determinedthe compositional range of stability of the e (Ag3Sb) phase usingX-ray powder diffraction measurements.

Thermodynamic assessment of this system was performed byLee et al. [48] and Oh et al. [49]. The latest thermodynamic assess-ment, including their own experimental results, was done by Zoroet al. [50].

3.4. Thermodynamic extrapolation of the Ag–Ge–Sb phase diagram

In this work phase diagram of the Ag–Ge–Sb ternary system hasbeen thermodynamically predicted using Gibbs energy values forpure elements (4.4SGTE) [51] and optimized thermodynamicparameters for the binary Ag–Ge system from Wang et al. [23],for the binary Ge–Sb from Liu et al. [39], and for the binary systemAg–Sb from Zoro et al. [50]. Calculations were performed usingPANDAT software [52].

parameters (J/mol) Ref.

779� 7:9876T [50]

1:357þ 7:1738T [50]

:0766 [50]

7� 6:822T [23]

:14þ 5:761T [23]

:56 [23]

:7� 0:5212T [39]

64:027þ 66:4033T [50]

:5741� 67:6783T [50]

:47þ 9:917T [23]

37:27 [23]

73:95þ 44:2101T [50]

1:9664� 49:1982T [50]

r þ 5000 [50]

r þ 5000 [50]

5GSerAg þ 0:25GSer

Sb � 411:8398� 3:8229T [50]

5GSerSb þ 0:25GSer

Ag þ 10411:8398þ 3:8229T [50]

788:5398 [50]

91:79 [50]

[50]

[50]

9210:1� 19:8000T [39]

10695:0� 6:5572T [39]

Table 2Considered phases and their crystal structures.

Thermodynamic database name Common name Space group symbol Strukturbericht designation Pearson’s symbol

LIQUID LiquidFCC_A1 (Ag) Rm3m A1 cF4HCP_A3 f (Ag9Sb) P63/mmc A3 hP2AGSB_ORTHO e (Ag3Sb) Pmm2 oP4RHOMBO_A7 (Sb) R3m A7 hR2

DIAMOND_A4 (Ge) Fd3m A4 cF8

Fig. 1. Calculated phase diagram of: (a) Ag–Ge [23], (b) Ge–Sb [39] and (c) Ag–Sb [50] binary system.

Fig. 2. Predicted liquidus projection of the ternary Ag–Ge–Sb system with markedoverall compositions of the investigated as-cast samples (blue squares). (Forinterpretation of the references to color in this figure legend, the reader is referredto the web version of this article.)

M. Premovic et al. / Journal of Alloys and Compounds 610 (2014) 161–168 163

Optimized thermodynamic parameters for the boundary binarysystems are listed in Table 1.

The phases from constitutive binary subsystems considered forthermodynamic calculation with their crystallographic data arelisted in Table 2.

Fig. 1 represents calculated phase diagrams of the constitutivebinary systems using thermodynamic parameters given in Table 1.

4. Results and discussion

4.1. Liquidus projection of the Ag–Ge–Sb ternary system

Preliminary investigation of the phase diagram and phase tran-sitions in the ternary Ag–Ge–Sb ternary system was done usingthermodynamic prediction of phase equilibria based on thermody-namic parameters obtained by [23,39,50]. Calculated liquidus pro-jection of the ternary Ag–Ge–Sb system is given in Fig. 2. Fig. 2shows predicted liquidus monovariant lines (in black) and the pri-mary crystallization fields together with calculated liquidus iso-therms (in red) with 50 �C temperature increments in the ternaryAg–Ge–Sb system.

Table 3Predicted invariant reactions involving the liquid phase in the Ag–Ge–Sb ternarysystem.

T (�C) Reaction x(Ag) x(Sb) Type

514.9 L + (Ag) ? (Ge) + f 0.705 0.203 U1

504.1 L + f ? (Ge) + e 0.694 0.222 U2

460.2 L ? (Ge) + (Sb) + e 0.560 0.380 E1

Fig. 3. SEM micrograph of the as-cast sample: (a) (Ag9.15Sb81.77Ge9.08), (b) (Ag59.85-

Sb19.17Ge20.98) and (c) (Ag81.07Sb10.01 Ge8.92).

164 M. Premovic et al. / Journal of Alloys and Compounds 610 (2014) 161–168

According to the results of thermodynamic extrapolation thereare totally five fields of primary crystallization: (Ge), (Sb), (Ag), e(Ag3Sb) and f (Ag9Sb). As it can be seen from Fig. 2, prevailing com-position region of primary crystallization belongs to the (Ge) solidsolution. Beside dominant composition region of (Ge) crystalliza-tion, there are significantly smaller primary crystallization fieldsof (Sb), (Ag), e and f phases, situated in the vicinity of the Ag–Sbboundary binary system.

Three ternary invariant reactions involving liquid phase havebeen predicted in the ternary Ag–Ge–Sb system. Two of them arequasi-ternary peritectic reactions or transition reactions (U-type)and the third reaction is ternary eutectic reaction (E-type). Pre-dicted invariant reactions as well as the corresponding reactiontemperatures and the compositions of ternary invariant pointsare listed in Table 3.

In order to experimentally study primary crystallization phasesand to make comparison with predicted results shown in Fig. 2,microstructures of four as-cast samples were investigated usingSEM–EDS.

Average overall chemical compositions of the investigated sam-ples in the as-cast state and determined average compositions ofco-existing phases obtained by EDS analysis are given in Table 4.

Experimentally determined overall compositions of the samplesA, B, C and D are marked in Fig. 2 for comparison with calculation.According to the results of thermodynamic binary-based predic-tion given in Fig. 2, (Ge) phase is predicted primary crystallizationphase for the samples B and C. Calculated primary crystallizationphases for the samples A and D are (Sb) and (Ag), respectively.

Characteristic SEM micrographs for the samples A, C and D withlabeled names of identified phases are presented in Fig. 3 as anillustration. Based on the results of SEM–EDS analysis, as-cast sam-ples A and B have three-phase microstructure: (Ge) (Sb) and e(Ag3Sb).

Fig. 3a represent microstructure of sample A. Large bright pri-mary solidified crystals of predominant (Sb) phase are visible inthe microstructure of the sample A, which is in agreement withpredicted liquidus projection. (Ge) and e phases are uniformly pre-cipitated at the (Sb) grain boundaries.

Sample C consist of two co-existing phases (Ge) and e (Ag3Sb)and microstructure of the sample D includes (Ge) and f (Ag9Sb)phases.

Table 4Experimentally determined overall and phase compositions of the as-cast samples of the Ag–Ge–Sb ternary system by EDS analysis.

Sample Overall composition (at.%) Determined phases Composition of phase (at.%)

Ag Sb Ge

A Ag9.15Sb81.77Ge9.08 (Ge) – 2.97 ± 0.25 97.03 ± 0.80(Sb) – 98.00 ± 0.80 2.00 ± 0.20e (Ag3Sb) 73.59 ± 0.85 26.41 ± 0.56 –

B Ag18.55Sb61.47Ge19.98 (Ge) – 1.05 ± 0.32 98.95 ± 0.20(Sb) – 97.79 ± 0.90 2.21 ± 0.40e (Ag3Sb) 73.50 ± 1.10 26.50 ± 0.45 –

C Ag59.85Sb19.17Ge20.98 (Ge) – 0.72 ± 0.20 99.28 ± 0.50e (Ag3Sb) 73.68 ± 0.95 26.32 ± 0.20 –

D Ag81.07Sb10.01 Ge8.92 (Ge) – 1.04 ± 0.20 98.96 ± 0.85f 87.31 ± 1.20 10.67 ± 0.40 2.02 ± 0.30

Table 5Experimentally determined (DTA) and predicted phase transition temperatures for selected samples of the ternary Ag–Ge–Sb system.

Alloy nominal composition (at.%) Phase transition temperatures (�C)

Solidus temperature Other peak temperature Liquidus temperature

Experimental Calculated Experimental Calculated Experimental Calculated

Ge–Ag50Sb50 vertical sectionGe20Ag40Sb40 477.1 460.2 – 502 652.5 636Ge40Ag30Sb30 477.6 460.2 – 502 766.4 754Ge60Ag20Sb20 478.2 460.2 – 502 821.3 817Ge80Ag10Sb10 477.5 460.2 – 502 873.5 870

Sb–Ag50Ge50 vertical sectionSb20 Ag40Ge40 476.8 460.2 – 483 784.3 775Sb40Ag30Ge30 477.2 460.2 509.5 518 715.5 700Sb60Ag20Ge20 477.4 460.2 533.5 538 654.3 614Sb80Ag10Ge10 476.7 460.2 562.3 546 588.4 572

Ag–Ge50Sb50 vertical sectionAg20Ge40Sb40 476.5 460.2 524.6 530 756.5 737Ag40Ge30Sb30 477.3 460.2 – 475 748.6 720Ag60Ge20Sb20 477.3 474.3 534.2 503 686.5 664Ag80Ge10Sb10 – 514.9 615.4 567 675.3 667

Fig. 4. Predicted vertical sections of the Ag–Ge–Sb ternary system compared with DTA results from the present study: (a) Ge–AgSb, (b) Sb–AgGe and (c) Ag–GeSb.

M. Premovic et al. / Journal of Alloys and Compounds 610 (2014) 161–168 165

Microstructure of the sample C is shown in Fig. 3b. The den-dritic morphology of the dark (Ge) phase indicates that this isthe primary solidification phase. This result is in agreement withpredicted liquidus projection (Fig. 2).

Predicted primary solidification phase (Ag) was not experimen-tally identified in the microstructure of the sample D (Fig. 3c). As itcan be seen from Table 4, only two detected phases for the sampleD are (Ge) and f. This could be explained by the occurrence ofpredicted invariant reaction L + (Ag) ? (Ge)+ f, which takes placeduring cooling and solidification of the sample D.

4.2. Results of thermal analysis

Phase transition temperatures of 12 selected samples withnominal overall compositions along three chosen isoplethsGe–Ag50Sb50, Sb–Ge50Ag50 and Ag–Ge50Sb50 were experimentallydetermined using DTA method. The solidus temperatures (firstpeak obtained during heating) were taken from the extrapolatedonset on heating. All others phase transition temperatures (peaks2 and 3) were taken from the peak maximum temperature [53]on heating. To check reproducibility of thermal effects and to

166 M. Premovic et al. / Journal of Alloys and Compounds 610 (2014) 161–168

estimate experimental uncertainty of obtained phase transitiontemperatures totally three heating runs were conducted for everyinvestigated sample. In general, the first heating cycle was ignoredand the mean value of temperatures on the second and thirdcurves was taken as the phase transition or the liquidus tempera-tures. The total experimental error of measured temperatures wasin the order of ±1 �C.

The comparative presentation of the extrapolated and experi-mentally determined average temperatures of phase transitionsobtained by DTA measurements are given in Table 5.

Comparison between calculated isopleths and experimentallydetermined phase transition temperatures is presented in Fig. 4.

According to the results of thermodynamic prediction shown inTable 5 and Fig. 4, solidus temperatures for all investigated sam-ples, except for the sample Ag80Ge10Sb10, correspond to the pre-dicted ternary eutectic reaction L M (Ge) + (Sb) + e at calculatedtemperature 460.2 �C. Experimentally determined solidus temper-atures of investigated samples are nearly identical, as it is expectedby the predicted ternary eutectic, but the average value of experi-mentally measured ternary eutectic temperature is 477.2 �C whichis considerably higher than predicted value of 460.2 �C.

Also, as can also be seen from Table 5 and Fig. 4, experimentallydetermined liquidus temperatures are significantly higher fromcorresponding predicted liquidus temperatures.

Fig. 5. DTA heating curve for the sample Ge40Ag30Sb30.

Table 6Predicted and experimentally determined phase compositions in the ternary Ag–Ge–Sb sy

Sample Overall composition (at.%) Determined phases Com

Theoretical SEM–EDS Ag

Exp.

1 29.03 Ge (Ge) (Ge) 0.237.33 Ag (Sb) (Sb) 0.733.64 Sb e (Ag3Sb) e (Ag3Sb) 72.2

2 70.94 Ge (Ge) (Ge) 0.312.82 Ag (Sb) (Sb) 0.816.24 Sb e (Ag3Sb) e (Ag3Sb) 72.8

3 14.33 Ge (Ge) (Ge) 1.09.44 Ag (Sb) (Sb) 0.576.23 Sb e (Ag3Sb) e (Ag3Sb) 72.6

4 28.83 Ge (Ge) (Ge) 0.253.77 Ag e (Ag3Sb) e (Ag3Sb) 74.417.40 Sb

5 14.65 Ge (Ge) (Ge) 0.875.00 Ag f f 85.610.35 Sb

DTA heating curve for the sample Ge40Ag30Sb30 is given in Fig. 5as an example. The extrapolated onset of the first peak at 477.6 �Cis related to the occurrence of ternary eutectic reaction (Ge) +(Sb) + e ? Liquid, while the second peak maximum temperature766.4 �C represents liquidus temperature.

4.3. Microstructure investigation of annealed samples

Microstructures of five chosen samples annealed at 400 �C wereinvestigated using SEM–EDS and XRD methods. Their overall com-positions and compositions of coexisting phases determined bySEM–EDS method as well as related calculated phase compositionsare given in Table 6.

The calculated isothermal section of the ternary Ag–Ge–Sb sys-tem at 400 �C and experimentally determined overall compositionsand phase compositions for five samples investigated using SEM–EDS are presented in Fig. 6. Experimentally obtained phase compo-sitions and overall compositions of individual samples are markedusing identical symbols with the same color.

Samples 1, 2 and 3 belong to the three-phase field(Ge) + (Sb) + e. Sample 4 is within two-phase field (Ge) + e as wellas sample 5 ((Ge) + f). Based on the results presented in Table 6

stem at 400 �C.

positions of phases (at.%)

Ge Sb

Cal. Exp. Cal. Exp. Cal.

2 ± 0.30 – 99.21 ± 0.20 100 0.57 ± 0.10 –3 ± 0.70 – 1.75 ± 1.00 1.18 97.52 ± 0.30 98.821 ± 0.90 74.20 1.08 ± 0.10 – 26.71 ± 0.20 25.80

9 ± 0.10 – 98.70 ± 1.00 100 0.91 ± 0.90 –9 ± 0.40 – 0.98 ± 0.10 1.18 98.13 ± 0.70 98.826 ± 0.80 74.20 0.89 ± 0.40 – 26.25 ± 0.50 25.80

7 ± 0.20 – 98.34 ± 0.90 100 0.59 ± 0.10 –7 ± 0.60 0.04 1.83 ± 0.40 1.18 97.60 ± 0.70 98.828 ± 0.20 74.20 0.85 ± 0.10 – 26.47 ± 0.50 25.80

5 ± 0.30 – 99.03 ± 0.60 100 0.72 ± 0.10 –5 ± 0.70 75.55 0.80 ± 0.10 – 24.75 ± 0.20 24.45

0 ± 0.20 – 98.69 ± 1.00 100 0.51 ± 0.50 –7 ± 0.40 87.87 2.11 ± 0.70 – 12.22 ± 0.10 12.13

Fig. 6. Calculated isothermal section of the ternary Ag–Ge–Sb system at 400 �Cwith overall and phase compositions for samples obtained by SEM–EDS analysis.

Fig. 7. SEM micrograph of the sample 1 (Ag37.33Ge29.03Sb33.64).

Fig. 8. SEM micrograph of the sample 4 (Ag53.77Ge28.83Sb17.40).

Fig. 9. XRD pattern for the alloy 1 (Ag37.33Ge29.03Sb33.64 (at.%)).

M. Premovic et al. / Journal of Alloys and Compounds 610 (2014) 161–168 167

and Fig. 6 it can be concluded that predicted phase structure ofinvestigated samples is in very good agreement with experimen-tally obtained results.

Fig. 7 is SEM micrograph of the sample 1 (Ag37.33Ge29.03Sb33.64)annealed at 400 �C for two weeks. Three different phases arevisible. Dark phase represent primary solidified (Ge) crystalsGrey and bright areas in the base represent uniformly distributede and (Sb) phases.

SEM micrograph of the sample 4 (Ag53.77Ge28.83Sb17.40) is pre-sented in Fig. 8. Microstructure of this sample includes two phases:dark primary solidified crystals of (Ge) phase in the predominantbase of e phase (bright areas).

Samples 1, 2 and 3 with overall composition given in Table 6were additionally investigated by XRD analysis. All samples are

Table 7Results of XRD analysis for the Ag–Ge–Sb samples annealed at 400 �C.

Sample Overall composition (at.%) Phase

Prediction E

1 29.03 Ge (Ge) (G37.33 Ag (Sb) (S33.64 Sb e (Ag3Sb) e

2 70.94 Ge (Ge) (G12.82 Ag (Sb) (S16.24 Sb e (Ag3Sb) e

3 14.33 Ge (Ge) (G9.44 Ag (Sb) (S76.23 Sb e (Ag3Sb) e

from the largest three-phase region ((Ge) + (Sb) + e) of isothermalsection at 400 �C (Fig. 6).

The results of XRD analysis are in mutual agreement with theresults of SEM–EDS analysis and thermodynamic prediction. Addi-tionally, lattice parameters of identified phases were determinedfrom XRD data and presented in Table 7.

XRD pattern for the sample 1 with identified phases is shown inFig. 9 as an illustration.

Obtained values of lattice parameters for (Ge) and (Sb) phasesare in good agreement with literature data [54,55]. By means ofX-ray diffraction Westgren et al. [56] studied the Ag–Sb systemin detail. They identified an orthorhombic structure and deter-mined the change in lattice parameters within the compositionof the e (Ag3Sb) phase for alloys annealed at 400 �C (a = 2.986–2.996 Å, b = 5.180–5.246 Å, c = 4.774–4.854 Å). Our results, pre-sented in Table 7, are in good agreement with the results publishedby Westgren et al. [56] and latest results by Lee et al. [57] and Linet al. [58].

5. Conclusion

Phase equilibria of the Ag–Ge–Sb ternary system have beenexperimentally investigated for the first time. Also, phase diagramof the Ag–Ge–Sb ternary system has been extrapolated usingoptimized thermodynamic parameters for the constitutive binarysystems from literature and compared with experimental data.Liquidus projection and invariant equilibria were calculated. Inthe experimental part of the work selected samples wereinvestigated using DTA, SEM–EDS and XRD methods. Theoccurrence of ternary eutectic reaction L M (Ge) + (Sb)+e has been

Lattice parameters (Å)

xperiment a b c

e) 5.6568(5) – –b) 4.2318(8) – 11.3740(2)(Ag3Sb) 2.9897(1) 5.2354(9)

e) 5.6568(3) – –b) 4.2643(6) – 11.3739(2)(Ag3Sb) 2.9932(2) 5.2353(1) 4.8524(1)

e) 5.6567(8) – –b) 4.3728(1) – 11.374(2)(Ag3Sb) 2.9908(1) 5.237(4) 4.8506(7)

168 M. Premovic et al. / Journal of Alloys and Compounds 610 (2014) 161–168

experimentally determined at measured temperature of 477.2 �Cwhich is significantly higher than predicted value 460.2 �C.Predicted isothermal section at 400 �C is in general agreement withthe results of microstructural investigations of annealed samplesobtained by SEM–EDS and XRD analysis although limited solubilityof Ge in the f (Ag9Sb) phase was detected. Lattice parameters ofidentified phases were determined using XRD analysis andcompared with literature data. Liquidus temperatures measuredon heating using DTA technique are fairly higher than correspond-ing predicted liquidus temperatures. Results presented in thisstudy provide a basis for a future experimental work andthermodynamic optimization/assessment of the Ag–Ge–Sb system.

Acknowledgement

This work has been supported by the Ministry of Education, Sci-ence and Technological Development of the Republic of Serbia,under Project No. ON172037.

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