Crystallization study of Sn additive Se–Te chalcogenide alloys

Thermochimica Acta 566 (2013) 274–280

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Crystallization study of Sn additive Se–Te chalcogenide alloys M.A. Abdel-Rahim, A. Gaber, A.A. Abu-Sehly, N.M. Abdelazim ∗ Physics Department, Faculty of Science, Assiut University, Assiut 71516, Egypt

a r t i c l e

i n f o

Article history: Received 25 February 2013 Received in revised form 5 June 2013 Accepted 8 June 2013 Available online 18 June 2013 Keywords: Se–Te–Sn system Crystallization kinetics Chalcogenide glasses Thermal analysis

a b s t r a c t Results of differential thermal analysis (DTA) under non-isothermal conditions of glasses Se90 − x Te10 Snx (x = 0, 2.5, 5 and 7 at.%) are reported and discussed. The glass transition temperature (Tg ), the onset crystallization temperature (Tc ) and the peak temperature of crystallization (Tp ) were found to be dependent on the compositions and the heating rate. Values of various kinetic parameters such as activation energy of glass transition (Eg ), activation energy of crystallization (Ec ), rate constant (Kp ), Hurby number (Hr ) and the order parameter (n) were determined. For the present systems, the results indicate that the rate of crystallization is related to thermal stability and glass forming ability (GFA). According to the Avrami exponent (n), the results show a one dimensional growth for the composition Se90 Te10 and a three dimensional growth for the three other compositions. The crystalline phases resulting from DTA and (SEM) have been identified using X-ray diffraction. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Chalcogenide glasses are of special interest due to their broad applications in modern electronics, optoelectronics, integrated optics, electro-photography, solar cells, electrical and optical memory devices etc. [1–4]. Among the amorphous chalcogenide alloys, mostly selenium (Se) based materials are preferred due to its commercial use. Moreover, its device applications like switching memory and xerography etc., made it attractive. But, the pure Se has a short life time and low sensitivity [5] although is characterized by high viscosity. The problem can be overcome by alloying selenium with some impurities such as Ge, Te etc., which in terms gives high sensitivity, greater hardness, high crystallization temperature and small aging effects as compared to pure Se glass [6]. Recently, it has been pointed out that Se–Te has some advantages over amorphous Se as far as their use in xerography is concerned [7] and the addition of Se to Te alloy improves the corrosion resistance [8]. The Se–Te alloys are found to be useful from the technological point of view if these alloys are thermally stable with time and temperature during use. On the other hand, the addition of a third element Sn impurity to Se–Te system increase thermal stability of the material. It has been found that the glass transition temperature increases with doping Sn content, indicating a cross linking of the Se–Te chains with the addition of Sn [9].

∗ Corresponding author. Tel.: +20 1223990118. E-mail address: [email protected] (N.M. Abdelazim). 0040-6031/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.tca.2013.06.009

Structural studies of chalcogenide glasses are important in determining the transport mechanisms, thermally stability and practical applications. Different techniques have been used to study the structure of chalcogenide glasses, e.g. electron microscopy, X-ray diffraction and differential scanning calorimetry. The studies of crystallization kinetics for these glasses using differential scanning calorimetry has been widely discussed in the literature [10–12]. Different theoretical models were proposed to explain the results of the crystallization kinetics. The application of the model depends on the glass composition and preparation conditions [13]. The present work is concerned with the study of the crystallization kinetics and deduce the crystallization parameter for Se90 − x Te10 Snx (where x = 0, 2.5, 5, 7.5 at. %) glasses using differential thermal analysis (DTA) under non-isothermal conditions. The effect of composition on the crystallization mechanism is discussed using different kinetics models.

2. Experimental techniques The bulk materials of Se90 − x Te10 Snx (x = 0, 2.5, 5, 7.5) were prepared by the usual melt quenching technique. The high pure materials (99.999%) were weighted according to their percentages and sealed in evacuated silica tubes then heated at 950 ◦ C for 20 h. During the melt, the tube was frequently rocked to intermix the constituents and to increase the homogenization of the melt. This treatment was followed by fast quenching in ice-water mixture. The glassy nature of the as-prepared and the crystalline phase structures for annealed samples was identified using a Philips

M.A. Abdel-Rahim et al. / Thermochimica Acta 566 (2013) 274–280 40 35

Se82.5 Te10 Sn7.5

30

DTA

25

Se85 Te10 Sn5

20 15

Se87.5 Te10 Sn2.5

10 5

Se90 Te10

0 -5 -10 325

350

375

400

425

450

475

500

525

550

575

600

Temp (K) Fig. 1. A typical DTA thermo-gram at heating rate 10 K/min for Se90x Te10 Snx (x = 0, 2.5, 5, 7.5).

diffractometer type 1710. DTA experiments were carried out on the as-prepared powder samples by using a Perkin–Elmer DTG60 under non-isothermal conditions. The values of the glass transition temperature (Tg ), the onset crystallization temperature (Tc ), the peak crystallization temperature (Tp ) and the melting temperature (Tm ) were determined with accuracy ±1 K using the micro processor of the thermal analyzer. The surface microstructures of the annealed Se–Te–Sn samples were examined using scanning electron microscopy (SEM) type JEOL JSM-T200. 3. Results and discussion Differential thermal analysis (DTA) experiments were performed at different heating rates ranging from 5 to 25 K/min to investigate the crystallization kinetics of Se90 − x Te10 Snx chalcogenide glasses under non-isothermal condition. Fig. 1 shows the thermo-grams of as-prepared Se90 − x Te10 Snx (x = 0, 2.5, 5 and 7.5 at. %) at a heating rate of 10 K/min. The DTA traces of all the samples show a single glass transition and single stage crystallization, which confirms the homogeneity of the samples. Similar thermo-grams are obtained for other heating rates (not shown here). Furthermore, the DTA thermo-grams show that glass transition temperatures (Tg ) and crystallization temperatures (Tp ) are observed at endothermic and exothermic peaks respectively. Furthermore, the Tg , Tc , and Tp shift to higher temperature with increasing heating rate. Numerical values of these temperatures at heating rate 10 K/min are listed in Table 1. The morphology of the studied compositions after annealing to crystallization temperature for half hour using the same heating and cooling rate as used in DTA measurements were examined by SEM. The sample was fractured and gold coated before SEM examination to study both the internal and surface morphology. The scanning micrographs of the annealed specimens of different

Table 1 The values of Tg , Tc , Tp , Tm , Tc − Tg and Hr for the studied compositions at heating rate 10 K/min. Composition

Tg (K)

Tc (K)

Tp (K)

Tm (K)

Tc − Tg (K)

Hr

Se90 Te10 Se87.5 Te10 Sn2.5 Se85 Te10 Sn5 Se82.5 Te10 Sn7.5

328.5 341 347.5 349

367.4 439 446.3 448.5

385.2 446.8 457.6 463

509 508.5 508 506

38.9 98 98.8 100

0.27 1.4 1.6 1.73

275

compositions are shown in Fig. 2(a–d). The microstructure of the composition Se90 Te10 annealed at 365 K is shown in Fig. 2(a). It is clear that crystalline phases are embedded in an amorphous matrix. Some of these crystallized particles are interconnected and others are isolated. Furthermore, the crystallites are dispersed homogeneously and occupy most of the structure. The microstructure obtained for the three other compositions annealed at 445 K are shown in Fig. 2(b–d). A polycrystalline structure consisting of nano-tubes embedded in an amorphous phases for the composition Se87.5 Te10 Sn2.5 is shown in Fig. 2(b). In general, further increase of Sn content in Se–Te–Sn system leads to polycrystalline structure consisting of different crystalline phases embedded in an amorphous matrix. Furthermore, the amount of the transformed crystalline phases decrease and the crystallized particles increase in size with increasing Sn content (Fig. 2(c) and (d)). In order to identify the crystalline phases that appeared in DTA and SEM examinations, the X-ray diffraction for as-prepared and annealed specimens at a temperature close to the crystallization temperature are shown in Fig. 3(a) and (b). Analysis of the X-ray diffraction pattern reveals that the amorphous structure for the as-prepared samples as shown in Fig. 3(a). On the other hand, the composition Se90 Te10 , which was annealed at 365 K for half hour has two phases Se and Se–Te embedded in an amorphous matrix as shown in Fig. 3b(i). Addition of Sn to the Se–Te system leads to the formation of new phase like Se–Te–Sn as shown in Fig. 3b(i–iv).

3.1. The glass transition region The glass transition region has been studied in terms of the activation energy of glass transition and the variation of glass transition temperature with composition and heating rate. The variation of Tg with composition for Se90 − x Te10 Snx (x = 0, 2.5, 5 and 7.5 at. %) at heating rate 10 K/min is shown in Fig. 4. It is clear that the glass transition temperature increases with increasing Sn content. On the other hand, the average coordination number Z increase with increasing Sn content (Fig. 4). The variation of Tg with the average coordination number is related as: Ln Tg = aZ + b

(1)

where Z denotes to the average coordination number per atom which is calculated in terms of covalent bonding. The Tg of a multi-component glass is known to depend on several independent parameters such as band gap, coordination number, effective molecular weight and the type and fraction of various structural units formed [14–16]. The increases of Tg with increasing Sn content in the present system may be explained by considering the structural changes occurring due to further addition of Sn content. The generally accepted structural model for amorphous Se includes two molecular species meandering chains, which contain helical chains of trigonal Se and Se8 ring molecules of monoclinic Se [5]. In the present case, the addition of Sn makes bonds with Se and is probably dissolved in the Se chains. Hence, the number of Se8 rings decreases while the number of long Se–Te polymeric chains and Se–Te mixed rings increases. It is known that the glass transition temperature Tg , should increase with increasing chain length and decrease with increasing ring concentration [5], hence Tg increases with increasing Sn content. Furthermore, we attribute the increase of Tg with increasing Sn content to the marginal increase, which occur in the coordination number (shown in Fig. 4) and the mean atomic masses of these glasses.

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Fig. 2. SEM micrographs showing the surface microstructure of the samples annealed for half hour (a) Se90 Te10 annealed at 365 K, (b) Se87.5 Te10 Sn2.5 , (c) Se85 Te10 Sn5 , and (d) Se82.5 Te10 Sn7.5 annealed at 445 K.

The dependence of Tg on the heating rate is analyzed through using two approaches. The first is the empirical relationship that has originally been suggested by Lasocka [17] and has the form: Tg = Ag + Bg ln ˇ

(2)

where Ag and Bg are constants for a given glass composition and ˇ is the heating rate used in DTA scans. It is evident from this equation that a plot of ln ˇ versus Tg should be a straight line for the studied compositions as shown in Fig. 5. The deduced Bg values for the studies composition are listed in Table 2. The change in the value of Bg with increasing Sn content for the studies compositions undergoes structural changes with incorporation of Sn.

(a)

The glass transition activation energy is the amount of energy, which is absorbed by a group of atoms in the glassy region, so that a jump from one metastable state to another is possible. This activation energy is involved in the molecular motion and rearrangement of atoms around Tg . The apparent activation energy of the glass transition Eg of the investigate glassy alloys are obtained using Kissinger’s formula [18]:

 ln

ˇ Tg2

 =−

Eg + const. RTg

(3)

where Eg is the activation energy for the glass transition and R is the universal gas constant. Fig. 6 shows the plot of ln (ˇ/Tg 2 )

(b)

Fig. 3. X-ray diffraction pattern for (a) specimens as-prepared and (b) for annealed ((i) Se90 Te10 annealed at 365 K for half hour, (ii) Se87.5 Te10 Sn2.5 (iii) Se85 Te10 Sn5 , and (iv) Se82.5 Te10 Sn2.5 ) annealed at 445 K for half hour).

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277

Sn % 5.90

-1

0

1

2

3

4

5

6

7

8

9

Se90 Te10 Se87.5 Te10 Sn2.5

-8.6 -8.8

5.88

-9.2

ln(β/Tp2)

5.86 5.84

ln(Tg)

Se85 Te10 Sn5 Se82.5 Te10 Sn7.5

-9.0

5.82

5 K/min 10 K/min 15 K/min 20 K/min 25 K/min

5.80 5.78

-9.4 -9.6 -9.8 -10.0 -10.2 -10.4 -10.6 -10.8

5.76

1.9

1.98

2.00

2.02

2.04

2.06

2.08

2.10

2.12

2.14

2.16

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

1000/Tp (K-1)

2.18

coordination number, Z Fig. 7. The plots of ln(ˇ/Tp 2 ) vs. 1000/Tp for the studied compositions. Fig. 4. Variation of Tg , Z with composition for bulk amorphous Se90 − x Te10 Snx at different heating rate.

Se90 Te10 Se87.5 Te10 Sn2.5

360

Se85 Te10 Sn5 Se82.5 Te10 Sn7.5

355

Tg (K)

verses 1000/Tg for Se90 − x Te10 Snx (where x = 0, 2.5, 5 and 7.5 at. %) glasses from which the activation energy for the glass transition Eg was evaluated and listed in Table 2. The Eg values lie in the range generally observed for chalcogenide glasses [6,10,19–21]. As shown in Table 2, the Eg values decrease with increasing Sn content. The decrease in Eg with Sn content is due to the increase in the internal energy [20], as more and more bonds formation increase, the internal energy of the glasses increases, therefore glass transition activation energy may be decreased with Sn content in Se–Te glasses.

350 345 340

3.2. Crystallization kinetics and activation energy:

335 330 325 320 1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4

ln β

The crystallization mechanism of amorphous material is controlled by nucleation and growth process, which can be characterized by the activation energy and dimensionality of growth process. In the present study, the kinetic analysis has been performed using three different theoretical models. The activation energy Ec of amorphous crystalline transformation were calculated using the equation derived by Kissinger [18]



Fig. 5. The plot of Tg vs. ln ˇ for the Se90 − x Te10 Snx chalcogenide glasse.

Se90 Te10 Se87.5 Te10 Sn2.5 -8.4

Se85 Te10 Sn5 Se82.5 Te10 Sn7.5

-8.6 -8.8

ln

ln(β/Tg2)

Tp2



ln

-9.4



= const. −

Ec RTp

(4)

Fig. 7 shows the plot of Ln (ˇ/Tp2 ) versus 1000/Tp for the studied compositions. From the slopes of the straight lines, the activation energies Ec for the crystallization process are deduced and listed in Table 3. The activation energy Ec and the frequency factor K0 are calculated using the method proposed by Augis and Banett [22]:

-9.0 -9.2

ˇ

ˇ (Tp − T0 )



= ln K0 −

Ec RTp

(5)

The plot of Ln[ˇ/(Tp − To )] versus 1000/Tp at different heating rates for all the investigated samples are shown in Fig. 8. From the slopes

-9.6 -9.8 -10.0 -10.2

Table 2 The values of Ag , Bg and Eg for the studied compositions.

-10.4 2.76

2.80

2.84

2.88

2.92

2.96

3.00

3.04

3.08

1000/Tg (K-1) Fig. 6. The plots of ln(ˇ/Tg 2 ) vs. 1000/Tg for the studied compositions.

Composition

Ag (K)

Bg (K)

Eg (KJ/mol)

Se90 Te10 Se87.5 Te10 Sn2.5 Se85 Te10 Sn5 Se82.5 Te10 Sn7.5

312.4 324.5 329.3 329.2

7.64 6.91 7.52 9.51

113.75 131.04 121.65 98.44

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3

Se85 Te10 Sn5 Se82.5 Te10 Sn7.5

0.8

ln(β/(Tp-To))

4

Se90 Te10 Se87.5 Te10 Sn2.5

1.0

0.6

2 1

ln(-ln(1-χ))

0.4 0.2 0.0 -0.2

-2 -3 -4

-0.6

-5

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

2.0

1000/Tp (K-1)

p

=−

Ec + constant RTp

(6)

where  is the volume fraction of crystallization, and Ln(d/dt)p is the maximum crystallization rate Fig. 9 shows the plot of Ln(d/dt)p

Table 3 The values of Ec , Ln K0 , Kp and n for the studied compositions. Composition

Ec (KJ/mol)

Se90 Te10 Se87.5 Te10 Sn2.5 Se85 Te10 Sn5 Se82.5 Te10 Sn7.5

2.4

2.6

2.8

3.0

3.2

3.4

Fig. 10. The plots of ln[−ln(1 − ␹)] versus ln ˇ at different temperatures for Se85 Te10 Sn5 .

of this function fitted to the data, we evaluated the activation energy for the crystallization processes are listed in Table 3, and the origin ordinate of these curves that gives the frequency factors K0 , which are given in Table 3 together with Ec . The activation energy of amorphous crystallization transformation for the studied compositions have also been deduced through the technique used by Gao-et al. [23], the maxima of the DTA curves are used and a relationship deduced by the authors is dt

2.2

ln β

Fig. 8. The plots of ln[ˇ/(Tp − T0 )] vs. 1000/Tp for the studied compositions.

 d 

At T=452 K At T=462 K At T=469 K

-6 1.9

n

Kp

Eq. (4)

Eq. (5)

Ln K0 Eq. (6)

Eq. (5)

Eq. (7)

Eq. (9)

72.4 86.17 96.64 103.73

54.77 72.17 77.14 80.02

49.02 51.38 54.23 55.55

16.84 19.69 20.36 20.58

2.16 3.5 3.6 4.1

5.6 × 10−4 4.3 × 10−4 4.4 × 10−4 4.5 × 10−4

against 1000/Tp . The Ec for the four compositions are determined and listed in Table 3. It can be noted from this table the activation energy (Ec ) of Se–Te–Sn glasses increases with increasing Sn content. As mentioned earlier [24,25] when Sn is added to Se–Te system it forms cross link structure which in turn retarded the tendency of crystallization resulting in an increase in the activation energy for crystallization. Furthermore, with the increase in Sn content the speed of crystallization decreases resulting in an increase in the activation energy for crystallization [24]. A study of the results for the Ec s obtained by the three different methods are reasonably different. These differences can be attributed to the fact that these models are based on approximations involved in obtaining the final equation of different formalisms. On the other hand, the Augis and Benett method is the conventional equation for evaluation of the activation energy because of the convenience and accuracy of the measurement of the heating rate. Furthermore this method is helpful in obtaining frequency factor K0 used for description of phase transformation. In addition to evaluation of activation energy Ec , dimensionality of growth and Avrami exponent has been evaluated from the method proposed by Ozawa [26]. It used to deduce the order of crystallization reaction (n) for continuous heating crystallization at fixed temperature. The volume fraction () of crystals precipitated in glass heated at a uniform rate (ˇ) is related to (n) through,

Se90 Te10 Se87.5 Te10 Sn2.5

3.0 2.8

Se85 Te10 Sn5 Se82.5 Te10 Sn7.5

2.6 2.4 2.2

ln (dχ/dt)

-1

-0.4

-0.8

Ln

0

2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

1000/Tp (K-1) Fig. 9. The plots of Ln (d/dt)p vs. 1000/Tp for the studied compositions.

d

{ln [− ln (1 − )} = −n d ln ˇ

(7)

As an example a plotting of ln [−ln (1−)] versus ln(ˇ) is shown in Fig. 10 for the composition Se85 Te10 Sn5 at three temperatures. The same procedure was used for the other compositions (not shown here). The average values of n as evaluated from the slope are listed in Table 3. The calculated n values were not integers and shows a variation in the range of 2.1 ≤ n ≤ 4.1, which indicates that, crystallization occurs through different mechanisms. These results are in good agreement with the results obtained by X-ray and SEM examination. Referring to the Avrami theory of nucleation, this means that the kinetic exponent (n) show predominantly a one-dimensional growth for binary Se90 Te10 (n = 2.1) whereas three dimensional growth for the other three compositions (3.5 ≤ n ≤ 4.1).

M.A. Abdel-Rahim et al. / Thermochimica Acta 566 (2013) 274–280

3.3. Thermal stability and glass forming ability: Determination and evaluation of the glass forming ability of chalcogenide glasses have been in the focus of attention and study for a long time. Kauzmanm [27] gives a criterion of good glass forming ability as reduced glass transition temperature, Trg ≥ 2/3. The ease of glass formation is determined by calculating the reduced glass transition temperature (Trg = Tg /Tm ). The value of Trg is found to be in the order of 2/3 indicating good glass forming ability for all the compositions of the investigated system. On the other hand, for a memory and switching material, the thermal stability and the glass forming ability (GFA) are vital importance. It has been found that Tc − Tg is a strong indicator of both the thermal stability and the GFA. The kinetic resistance to crystallization is given by the difference between Tc and Tg . The larger difference gives higher resistance to crystallization. Values of difference of glass transition temperature and crystallization temperature for glassy alloys of Se90 − x Te10 Snx are given in Table 1. It is obvious from this table that (Tc − Tg ) is higher for Sn additive Se–Te systems indicating that the addition of Sn content to the Se–Te system made it thermally more stable. These results are in good agreement with other workers [28–31]. Another parameter usually employed to estimate the Glass Forming Ability (GFA) is the one introduced by Hruby [32] and defined, Hr =

Tc − Tg Tm − Tc

(8)

where Tm is the peak melting temperature. The parameter Hr gives the probability of obtaining a glass which increase as (Tm − Tc ) decreases and (Tc − Tg ) increases. It is usually difficult to prepare glasses with Hr < 0.1 while good glasses can be formed if Hr > 0.5 [32]. The average deduced values of Hr for the studied compositions are listed in Table 1. The table reveals that the GFA increase with increasing Sn content. Therefore, the stability of the glass increase with increasing Sn content. On the other hand, to obtain information about the morphology of the growth the following equation from the Gao-Wang model [33] has been used to calculate the value of the rate constant (Kp ) for a constant heating rate Kp =

ˇEc RTp2

(9)

The high values of Kp means a poor stability and a low GFA. The average values of rate constant Kp are calculated by using Eq (9) and listed in Table 3. It is clear from this table that Kp decrease with an increase Sn content and the values of the Hruby number Hr increase with increasing the Sn content. So from Table 1 we can say that the Hruby number (Hr ) is just opposite to that of the rate constant (Kp ). Thus the stability based on the criterion of the rate constant agrees with criterion based on Hr . Hence one can conclude that the rate of the crystallization is related to the thermal stability and the glass-forming ability (GFA) in the present glasses. This fact is also confirmed by Ec and K0 values given in Table 3. It is clear from this table that the activation energy Ec of amorphous crystalline transformation increases with increasing Sn content in the present system. Such result indicates that the rate of crystallization decrease with increasing Sn content. On the other hand, the frequency factor K0 (which measures the probability of molecular collisions effective for the formation of the activation complexes in each case). This effect implies a smaller crystallization tendency in glasses containing larger concentration of Sn. 4. Conclusion The results of thermal analysis measurements performed at various heating rates on Se90 − x Te10 Snx (x = 0, 2.5, 5 and 7.5 at. %)

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are reported and discussed. The results show that all compositions have a single glass transition and single stage crystallization. The observed dependence of Tg on heating rates was used to evaluate Eg . The crystallization behavior of these glasses has been studied under non-isothermal conditions. The crystallization parameter namely Tc , Tp , (Tc − Tg ), K0 , Kp and Ec were found to be dependent on the composition. The results indicate that the mechanism of crystallization in Se90 − x Te10 Snx occurs in one and three dimensional growth according to the Avrami exponent. The calculated activation energy of crystallization (Ec ), the glass formation ability (GFA) and the frequency factor (K0 ) indicate that the rate of crystallization decrease with increasing Sn content. References [1] S. R-Ovshinsky, H. Fritzsche, Reversible structural transformation of amorphous semiconductor for memory and logic, Met. Trans. 2 (1971) 641. [2] S. Surinach, M.D. Baro, M.T. Clavaguera-Mora, N. clavaguera, Kinetic study of isothermal and continuous heating crystallization in GeSe2 GeTe Sb2 Te3 alloy glasses, J. Non-Cryst. Solids 58 (1983) 209. [3] M.A. Abdel-Rahim, A.H. Moharram, M. Dongol, M.M. Hafiz, Experimental studies of the Ge–Sb–Se system, J. Phys. Chem. Solids 51 (1990) 355. [4] M.M. Hafiz, A.H. Moharram, M.A. Abdel-Rahim, A.A. Abu-Sehly, The effect of annealing on the optical absorption and electrical conduction of amorphous As24.5 Te71 Cd4 .5 thin films, Thin Solids Films 292 (1997) 7. [5] S.A. Khan, M. Zulfequar, M. Husain, On the crystallization kinetics of amorphous Se80 In20 − x Pbx , Solid State Commun. 123 (2002) 463. [6] N. Suri, K.S. Bindra, P. Kumar, R. Thangaraj, Calorimetric studies of Se80 − x Te20 Bix bulk samples, J. Non-Cryst. Solids 353 (2007) 1264. [7] N. Afify, M.A. Hussein, N. El-kabany, Structural transformation on Se0.8 Te0.2 chalcogenide glass, J. Non-Cryst. Solids 354 (2008) 3260. [8] R. Chiba, N. Funakoshi, Crystallization of vacuum deposited Te–Se–Cu alloy film, J. Non-Cryst. Solids 105 (1988) 149. [9] S.K. Tripathi, V. Sharma, Effect of Sb additive on the electrical properties of Se–Te alloy, J. Non-Cryst. Solids 351 (2005) 2468. [10] M.A. Abdel-Rahim, A.Y. Abdel-latif, A.S. Soltan, Structural study of chalcogenide Ge20 Se50 Te30 glass, Phys. B 291 (2000) 41. [11] J. Vazwez, C. Wanger, P. Villares, R. Jimenez-Garay, Glass transition and crystallization kinetics in Sb0:18 As0:34 Se0:48 glassy alloy by using non-isothermal techniques, J. Non-Cryst. Solids 335 (1998) 548. [12] M.K. Rabinal, K.S. Sangunni, E.S.R. Gopal, Chemical ordering in Ge20 Se80−␹ In␹ glasses, J. Non-Cryst. Solids 188 (1995) 98. [13] D.W. Henderson, Thermal analysis of non-isothermal crystallization kinetics in glass forming liquid, J. Non-Cryst. Solids 30 (1979) 301. [14] A. Giridhar, S. Mahadevan, Studies on the As–Sb–Se glass system, J. Non-cryst. Solid 51 (1982) 305. [15] K. Tanka, Structural phase transitions in chalcogenide glasses, Phys. Rev. B 39 (1989) 1270. [16] M.A. Abdel-Rahim, Crystallizion kinetics of selenium–tellerium glasses, J. Mater. Sci. 27 (1992) 1757. [17] M. Lasocka, The effect of scanning rate on glass transition temperature of splatcooled Te85 Ge15 , Mater. Sci. Eng. 23 (1976) 173. [18] H.E. Kissinger, Variation of peak temperature with heating rate in differential thermal analysis, J. Res. Natl. Bur. Stand. 57 (1956) 217. [19] M.A. Abdel-Rahim, A. El-Korashy, M.M. Hafiz, A.Z. Mahmoud, Kinetic study of non-isothermal crystallization of Bix Se100 − x chalcogenide glasses, Phys. B 403 (2008) 2956. [20] S. Faheem Naqvi, Deepika, N.S. Saxena, K. Sharma, D. Bhandari, Glass-crystal transformations in Se80 − x Te20 Agx (x = 0, 3, 5, 7 and 9) glasses, J. Alloys Compd. 506 (2010) 956. [21] G. Kaur, T. Komatsu, Crystallization kinetics of bulk amopphous Se–Te–Sn system, J. Mater. Sci. 35 (2000) 903. [22] J.A. Augis, J.E. Bennett, Calculation of the avrami parameters for heterogeneous solid state reactions using a modification of the Kissinger method, J. Therm. Anal. 13 (1978) 283. [23] Y.Q. Gao, W. Wang, F.Q. Zheng, X. Liu, On the crystallization kinetics of Pd80 B4 Si16 glass, J. Non-Cryst. Solids 81 (1986) 135. [24] S. Kumar, K. Singh, The effect of indium additive on crystallization kinetics and thermal stability of Se–Te–Sn chalcogenide glasses, J. Phys. B 406 (2011) 1519. [25] F. Abdel-Wahab, Observation of phase separation in some Se–Te–Sn chalcogenide glasses, J. Phys. 406 (2011) 1053. [26] T. Ozawa, Kinetics of non-isothermal crystallization, Polymer 12 (1971) 150. [27] W. Kauzmann, The nature of the glassy state and the behavior of liquids at low temperature, Chem. Rev. 43 (1948) 219. [28] M.A.A. Abdel-Rahim, A. El-Korashy, S. Al-Ariki, Crystallization studies on Se–Te–Cd chalcogenide glasses, Mater. Trans. 51 (2) (2010) 256. [29] S. Kumar, K. Singh, The effect of indium additive on crystallization kinetics and thermal stability of Se–Te–Sn chalcogenide glasses, Phys. B 406 (2011) 1519.

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