I D Olekseyuk, Yu M Kogut, O V Parasyuk - Glass-formation in the ag2se-zn(cd,hg)se-gese2 systems - страница 1

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Chemistry of Metals and Alloys

Chem. Met. Alloys 2 (2009) 146-150 Ivan Franko National University of Lviv www. chemetal-j ournal. org

Glass-formation in the Ag2Se-Zn(Cd,Hg)Se-GeSe2 systems

I.D. OLEKSEYUK1, Yu.M. KOGUT1*, O.V. PARASYUK1, L.V. PISKACH1, G.P. GORGUT1, O.P. KUS'KO1, V.I. PEKHNYO2, S.V. VOLKOV2

Department of General and Inorganic Chemistry, Lesya Ukrainka Volyn National University, Voli Ave 13, 43025 Lutsk, Ukraine 2 V.I. Vernadskii Institute for General and Inorganic Chemistry of the Ukrainian National Academy of Sciences,

Palladina Ave 32/34, 03680 Kyiv, Ukraine * Corresponding author. Tel.: +38-03322-49972; fax: +38-03322-41007; e-mail: luchanyn@yahoo.com

Received November 11, 2009; accepted December 23, 2009; available on-line April 27, 2010

The glass-formation regions in the quasi-ternary systems Ag2Se-Zn(Cd,Hg)Se-GeSe2 were determined using XRD data. The maximum content of the modifier ZnSe is 10 mol.%, that of CdSe is 12 mol.%. The largest region of existence of glasses is observed in the mercury-containing system where it crosses the concentration triangle. The thermal properties of the glasses were characterized by the glass transition temperature, the crystallization temperature and the melting point of the crystallized alloy.

Chalcogenide glasses / Quasi-ternary systems / Characteristic temperatures

Introduction

Complex chalcogenide semiconductor glasses (CSGs) are widely used in various applications of optics and electronics (see e.g. [1]) due to good transparency in the infra-red spectral region. A proven approach to widen the range of applications and to progress into new fields consists in doping the material. For instance, when doped with rare-earth ions, CSGs with low phonon energies are expected to be efficient host materials for fiber-optic amplifiers and IR lasers [2].

Germanium selenide is an effective glass-forming compound that has recently drawn interest as the matrix for functional membranes in ion-selective potentiometry, particularly for heavy metal ions [3]. The use of glasses provides higher chemical stability in corrosive media and better selectivity in the presence of interfering ions than crystalline electrodes.

An investigation of glass formation in the quasi-binary system HgSe-GeSe2 revealed a large region of existence of glasses - from 50 to 100 mol.% GeSe2 [4]. These glassy alloys exhibit a photodarkening effect and are promising materials for devices of high-density optical recording of information. It was shown in [5] that addition of Cu2Se (maximum content 6 mol.%) leads to a significant increase of the photoconductivity of the HgSe-GeSe2 glasses, which makes possible their use as materials for photosensors. It is expected that the modification of these glasses with silver selenide - an analog of Cu2Se - will increase the glass-formation region and thus widen the range of control over the properties of the glasses.

Additionally, glasses modified with silver chalcogenides are expected to possess high ionic conductivity due to the Ag+ ions, making them a promising base for the development of new materials. In some ternary Ag- and Ge-containing chalcogenide glasses the conductivity is almost entirely due to ionic transport, with an ionic transport number close to unity [6].

Considering the interesting properties of the glasses in the boundary systems, we decided to investigate the properties of multicomponent GeSe2-based glasses modified with selenides of both silver and Group II-b elements. Presently, we report the results of the investigation of the glass-formation regions in the Ag2Se-Zn(Cd,Hg)Se-GeSe2 systems and thermal properties of the glasses.

Data on the glass formation and properties in the Ge-Cd-Se system were reported in [7]. It was discovered that the glass compositions in the GeSe2-CdSe section occupy a minor concentration range near GeSe2 that does not exceed a few mol.%. A similar picture was observed in the GeSe2-ZnSe system [8]. A preliminary investigation of the Ag2Se-GeSe2 system [9] indicated that the glass-formation region is small and is localized near the binary eutectic at 57 mol.% GeSe2.

An investigation of the phase equilibria in the Ag2Se-ZnSe-GeSe2 system [10] revealed no ternary or quaternary zinc-containing compounds. The study of the Ag2Se-CdSe-GeSe2 system, in addition to the known ternary compounds Ag8GeSe6 and Cd4GeSe6 [11],    discovered    the    quaternary compounds

Ag2CdGe2Se6 and Ag2CdGeSe4 [10]. The ternary compound Hg2GeSe4 was reported in [12]. The Ag2Se-HgSe-GeSe2 system was investigated in detail in [13]. A compound with the approximate composition Ag1.4Hg1.3Ge2Se6 was discovered, as well as four solid solution ranges along the section Ag8GeSe6-'Hg4GeSe6'. Their extent is expressed by

the compositions Ag7.12-6.32Hg0.44-0.82GeSe6,

Ag6.06-4.00Hg0.96-2.00GeSe6, Ag3.4Hg2.3GeSe6, and Ag2.24-2.00Hg2.88-3.00GeSe6. The quaternary compound Ag2HgGeSe4, reported in [14], was not observed.

Experimental

Glassy alloys of the studied systems were synthesized from high-purity elements (at least 99.99 wt.% of the principal component) and previously synthesized HgSe for the mercury-containing system. The alloys were heated to 1270 K at a rate of 40-50 K/h, held at this temperature for 10 h for homogenization of the melt, and quenched into a saturated aqueous sodium chloride solution. The cooling rate during quenching was estimated to >200 K/s [15]. The obtained glasses were black ingots with a characteristic shine. The samples were studied by powder XRD (a DRON 4-13 diffractometer, 10-60° 26 range, 3 s exposure) for the determination of the glass-formation region. The characteristic temperatures of the glassy alloys were determined by DTA (a Paulik-Paulik-Erdey derivatograph, heating rate 10 K/min). The accuracy of the measurements of the thermal effects was ±5 K.

Results and discussion

The results of the determination of the glass-formation regions in the quasi-ternary systems Ag2Se-Zn(Cd,Hg)Se-GeSe2 are presented in Fig. 1. The glass-formation region in the boundary system Ag2Se-GeSe2 is limited to the range 53-56 mol.% GeSe2. The maximum amount of zinc or cadmium selenide that can be introduced into the glass is 10 mol.% ZnSe or 12 mol.% CdSe. The maximum GeSe2 content is 63 mol.% at 4-6 mol.% ZnSe, whereas for the Cd-containing glasses it equals 62 mol.% at 8 mol.% CdSe. It is suggested that at this ZnSe or CdSe concentration the glass-formation regions are localized near the binary or ternary eutectics in the respective stable phase diagrams.

Increase of the covalent component of chemical bonding and decrease of the liquidus temperature from ZnSe to CdSe, and especially to HgSe, are the main contributing factors to the existence of a much larger glass-formation region in the Ag2Se-HgSe-GeSe2 system (Fig. 1), where it crosses the concentration triangle. The minimum content of the glass-forming component is 43 mol.% GeSe2. For GeSe2 concentrations over 80 mol.% the glass-formation region narrows along the HgSe-GeSe2 side, and the content of the modifier Ag2Se does not exceed 3 mol.%.

Fig. 1 Glass-formation regions in the Ag2Se-Zn(Cd,Hg)Se-GeSe2 systems.

Characteristic temperatures of the glassy alloys, namely the glass transition temperature (Tg), the crystallization temperature (Tc), and the melting point (Tm) of the crystallized alloy, were measured. Using these data, the reduced glass-formation temperature Tgr was calculated as Tgr=Tg/Tm. The results are presented in Tables 1-3. If more than one exothermic effect of crystallization was recorded (e.g. alloys 1-4, 2-9, 3-14), the alloys in question were composed of several glassy phases.

The glass transition temperature of the ZnSe- and the CdSe-containing glasses lies in a fairly narrow range (526±8 K), probably because the regions of glass existence are themselves rather small. The temperature range agrees well with the data for the HgSe-containing alloys with similar modifier concentration (up to 20-25 mol.% of the Group II selenide).

Table 1 Composition of glassy alloys of the quasi-ternary system Ag2Se-ZnSe-GeSe2 and their characteristic temperatures.

No.

Composition, mol.%

Tg, k

Tc, K

Tm, K

T

 

Ag2Se

ZnSe

GeSe2

 

 

 

 

1-1

47

-

53

528

603, 627

859

0.61

1-2

45

2

53

520

612

856

0.61

1-3

43

2

55

526

624, 640

859

0.61

1-4

41

2

57

528

585, 622

859

0.61

1-5

43

4

53

523

610

851

0.61

1-6

41

4

55

527

621

851

0.62

1-7

39

4

57

530

619

850

0.62

1-8

37

4

59

526

617

858

0.61

1-9

35

4

61

522

616

850

0.61

1-10

33

4

63

533

615

867

0.61

1-11

41

6

53

526

615

853

0.62

1-12

39

6

55

526

607

849

0.62

1-13

37

6

57

526

617

850

0.62

1-13

35

6

59

519

620, 667

850

0.61

1-15

33

6

61

527

612, 670

842

0.63

1-16

31

6

63

526

610

858

0.61

1-17

37

8

55

523

605

852

0.61

1-18

35

8

57

526

603

846

0.62

1-19

28.5

9.5

62

526

603

878

0.60

Table 2 Composition of glassy alloys of the quasi-ternary system Ag2Se-CdSe-GeSe2 and their characteristic temperatures.

No.

Composition, mol.%

Tg, к

Tc, к

Tm, K

T

 

Ag2Se

CdSe

GeSe2

 

 

 

 

2-1

45

2

53

526

623

852

0.62

2-2

42

3

55

525

622

855

0.61

2-3

42

4

54

534

624

869

0.61

2-4

40

4

56

526

620

860

0.61

2-5

35

5

60

527

623

863

0.61

2-6

41

7

52

527

622

863

0.61

2-7

39

7

54

526

624

860

0.61

2-8

37

7

56

525

624

858

0.61

2-9

30

8

62

526

617, 669

867

0.61

2-10

38

10

52

531

622, 628

861

0.62

2-11

36

10

54

527

623

861

0.61

However, the HgSe glasses exhibit a much wider divergence of values of both Tg and Tc. The dependences of Tg and Tc on the HgSe concentration are plotted for an Ag2Se concentration of 5 mol.% (Fig. 2) and for a fixed GeSe2 concentration of 50 mol.% (Fig. 3) (to illustrate more fully the findings, we extended the range of the graphs by including data for samples with 2 mol.% Ag2Se-46 mol.% GeSe2-52 mol.% HgSe and 2 mol.% Ag2Se-83 mol.% GeSe2-15 mol.% HgSe.).

The glass transition temperature near the HgSe-GeSe2 boundary system (Fig. 2) decreases gradually with increasing HgSe content and features a minimum near 45-50 mol.% HgSe. The Tc values decrease as well, but to a lesser extent.

Within the concentration triangle, the values of Tg can be subdivided into three sharply defined regions (Fig. 3): 528±6 K for a HSe content up to 20-25 mol.%, 498±6 K for the HgSe range 25-40 mol.% and a distinct Tg minimum at 465-470 K near 45-50 mol.% HgSe. These regions most likely correspond to different fields of primary and secondary crystallization in the stable phase diagram of this quasi-ternary system (which is not yet fully investigated). The transition between different fields of crystallization leads to a different order of the formation of structural units that, in glasses, results in regions of different glass-formation temperature. The variations of Tc within the triangle are not pronounced.

Table 3 Composition of glassy alloys of the quasi-ternary system Ag2Se-HgSe-GeSe2 and their characteristic temperatures.

No.

Composition, mol.%

Tg, к

Tc, к

 

T

 

Ag2Se

HgSe

GeSe2

 

 

 

 

3-1

2

15

83

552

639

962

0.57

3-2

2

52

46

500

608

852

0.59

3-3

3

20

77

543

636, 726

939

0.58

3-4

4

20

76

544

634, 715

943

0.58

3-5

5

20

75

527

640

938

0.56

3-6

5

25

70

526

648, 730

922

0.57

3-7

5

30

65

503

641, 728

920

0.55

3-8

5

35

60

493

626

888

0.56

3-9

5

40

55

492

613

876

0.56

3-10

5

45

50

466

604

855

0.55

3-11

5

50

45

469

603

841

0.56

3-12

10

30

60

492

629

895

0.55

3-13

10

45

45

470

606, 672

848

0.55

3-14

12

45

43

469

600, 648

850

0.55

3-15

15

25

60

527

630

886

0.59

3-16

18

32

50

495

596

863

0.57

3-17

20

15

65

526

618

893

0.59

3-18

20

25

55

527

607, 690

871

0.61

3-19

20

35

45

498

607, 633

849

0.59

3-20

25

15

60

526

619

875

0.60

3-21

30

10

60

527

625, 632

869

0.61

3-22

30

25

45

494

602, 645

863

0.57

3-23

35

10

55

527

612

866

0.61

3-24

35

20

45

492

602

847

0.58

3-25

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