Non-isothermal Differential scanning calorimetry (DSC) technique was used to study the kinetics of first order phase transformation in Ge25Se75 – xSbx glasses. The X-ray diffraction (XRD) technique was employed to investigate the amorphous and crystalline phases in Ge25Se75 – xSbx glasses. From the heating rate dependences of crystallization temperature; the activation energy for crystallization and other kinetics parameters were derived. The temperature difference (Tc – Tg) and Tc is highest for the samples with 6 % of Sb. Hence, Ge25Se69Sb6 glass is most stable. The enthalpy released is found to be less for Ge25Se69Sb6 glass which further confirms its maximum stability. The activation energy of crystallization (Ec) is found to vary with compositions indicating a structural change due to the addition of Sb. The crystallization data are interpreted in terms of recent analyses developed for non-isothermal conditions. The present investigation indicates that both the glass transition and the crystallization processes occur in a single stage.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3101

Al-Agel, F.A.

Al-Arfaj, E.A.

Al-Ghamdi, A.A.

Al-Marzouki, F.M.

Husain, M.

Khan, Shamshad A.

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 5 No 2, 02021(4pp) (2013) Том 5 № 2, 02021(4cc) (2013) 
 
 
2077-6772/2013/5(2)02021(4) 02021-1  2013 Sumy State University 
First Order Phase Transformation in Amorphous Ge25Se75 – xSbx Glasses 
 
F.A. Al-Agel1, F.M. Al-Marzouki1, A.A. Al-Ghamdi1, Shamshad A. Khan2, E.A. Al-Arfaj3, M. Husain4 
 
1 Department of Physics, King Abdulaziz University, Jeddah-21589, Saudi Arabia 
2 Department of Physics, St. Andrew’s College, Gorakhpur, UP 273001, India 
3 Department of Physics, College of Applied Sciences, Umm Al-Qura University, Makkah, Saudi Arabia 
4 Department of Physics, Jamia Millia Islamia, New Delhi-110025, India 
 
(Received 15 February 2013; revised manuscript received 06 May 2013; published online 07 May 2013) 
 
Non-isothermal Differential scanning calorimetry (DSC) technique was used to study the kinetics of 
first order phase transformation in Ge25Se75 – xSbx glasses. The X-ray diffraction (XRD) technique was em-
ployed to investigate the amorphous and crystalline phases in Ge25Se75 – xSbx glasses. From the heating rate 
dependences of crystallization temperature; the activation energy for crystallization and other kinetics pa-
rameters were derived. The temperature difference (Tc – Tg) and Tc is highest for the samples with 6 % of 
Sb. Hence, Ge25Se69Sb6 glass is most stable. The enthalpy released is found to be less for Ge25Se69Sb6 glass 
which further confirms its maximum stability. The activation energy of crystallization ( Ec) is found to 
vary with compositions indicating a structural change due to the addition of Sb. The crystallization data 
are interpreted in terms of recent analyses developed for non-isothermal conditions. The present investiga-
tion indicates that both the glass transition and the crystallization processes occur in a single stage. 
 
Keywords: Glass transition temperature, Crystallization kinetics, X-Ray diffraction, Phase transformation. 
 
 PACS numbers: 71.55.Jv, 65.90. + I, 67.80.Gb, 73.61.Jc 
 
 
1. INTRODUCTION 
 
Amorphous chalcogenide glasses have been investi-
gated extensively over the past few decades. These 
glasses have been widely used in device technology and 
the current interest in these materials centers on X-ray 
imaging and photonics [1]. The relevance of studying 
the phase transformation in these materials has a tech-
nological aspect, since several physical properties 
change in the temperature range of utilization of the 
materials. It is also of fundamental scientific interest, 
since one can obtain useful information on the elemen-
tary processes, which modify the structure of an amor-
phous system, eventually producing stable phases on 
crystallization. The study the first order phase trans-
formation in chalcogenide glasses by the differential 
scanning calorimetry (DSC) method has been widely 
discussed in literatures [2-8]. The first order phase sep-
aration effects are of general interest in chalcogenide 
glasses. It is a term used to describe a phenomenon 
where an initially homogeneous system, such as a liq-
uid, will unmix into two or more finely mixed chemically 
or structurally different, component or phases. Such 
structural effects produce usually pronounced changes 
in glass physical properties including a lowering of the 
glass transition temperature, a lowering of the optical 
band gap, an increase of molar volumes [9]. The phase 
transformation can exist on a variety of length scales 
from nanometers to micrometers or millimeters [9]. For 
the purpose of photonic applications, it is important 
that phase separation be eliminated or at least mini-
mized to length scales much smaller than that the 
wavelengths of light being used. Apart from the tech-
nical importance, the knowledge of crystallization kinet-
ics is very important for a better understanding of 
amorphous structure of such chalcogenide glasses. 
The study of glass transition kinetics in chalcogenide 
glasses is of great importance to establish the thermal 
stability, glass-forming ability and ultimately to deter-
mine the useful range of operating temperatures for a 
specific technological application before the eventual 
crystallization takes place. The glass forming tendency 
of the glassy alloys is related to ease by which melt can 
be cooled with the avoidance of crystal formation. 
Meanwhile, the thermal stability indicates the re-
sistance of crystallization of glassy alloy through the 
nucleation and growth process. To evaluate the glass 
forming tendency and thermal stability of chalcogenide 
glasses, different simple quantitative methods are usu-
ally used. The most commonly used methods are those 
suggested by Kissinger [10] and Ozawa [11], which are 
based on some characteristic temperatures such as the 
glass transition and crystallization temperatures moni-
tored by the differential scanning calorimeter (DSC). 
The present work reports first order phase trans-
formation in amorphous Ge25Se75 – xSbx glasses by using 
non-isothermal DSC measurements. The effect of varia-
tion of Sb content on the thermal stability and glass 
forming tendency has also been studied. In the present 
system, we have used Se as a major content because it 
is widely used as a typical glass-former. The choice of 
selenium is due to its wide commercial importance. Its 
device applications like rectifiers, photocells and switch-
ing memory, etc. have made it attractive. But the pure 
selenium has low sensitivity and short lifetime. In order 
to overcome this difficulty, several workers have used 
certain additives (Ga, Ge, Bi, etc.) for alloying Se to 
some extent. We have chosen germanium as an additive 
material. Germanium is also known to contribute to 
long-term room temperature stability [12]. We have 
incorporated Sb as the third element in Ge-Se alloys. 
The continued scientific interest in Sb based chalco-
genide glasses is due to its potential use in phase 
change optical recording [13-18]. In phase change opti-
cal recording, the recording of information is based on 
writing and erasing of amorphous marks in a crystalli-
zation layer of a phase change material. Since the opti-
cal properties of the amorphous phases are different 
from those of the crystallization phase, the written 
mark can be read out as a contrast in the reflectance. 
Besides sufficient optical contrast between the crystal-
line and amorphous state, the thermal stability and 
 F.A. AL-AGEL, F.M. AL-MARZOUKI, A.A. AL-GHAMDI, ET AL. J. NANO- ELECTRON. PHYS. 5, 02021 (2013) 
 
 
02021-2 
glass forming tendency are one of the most important 
issues in developing phase change materials. In chalco-
genide glasses, glass forming tendency and thermal 
ability of a glassy alloy is related to the ease by which 
melt can be cooled with the avoidance of crystal for-
mation. The thermal stability and glass forming ten-
dency play an important role in determining the utility 
of chalcogenide alloys as recording material [19-23]. 
The knowledge of the thermal stability and glass form-
ing tendency in Ge25Se75 – xSbx glasses is, therefore, a 
subject of great interest. 
 
2. EXPERIMENTAL DETAILS 
 
Amorphous glassy alloys of Ge25Se75 – xSbx with x  6, 
9 12 and 15 were prepared by melt quenching technique. 
The highly pure materials (99.999 % pure) were weighed 
according to their atomic percentages and sealed in 
quartz ampoules under a vacuum of 10 – 6 Torr using 
turbo pump. The sealed ampoules were then placed in a 
Microprocessor Controlled Programmable Muffle Fur-
nace with rocking mechanism. The temperature of the 
furnace was increases at three stems. Initially at 773 K 
for 4 hours, then 973 K for 4 hours, and finally at 1273 K 
for 6 hours. The rocked motion accomplishes a complete 
mixing of the materials in the ampoule. Rapid quenching 
in ice-water bath was used to obtain the bulk amorphous 
material. By breaking the ampoule, ingots of the sample 
were taken out and then using ceramic tools the amor-
phous material was crushed in to a fine powder.  Thin 
films of Ge25Se75 – xSbx glasses were prepared on Si (100) 
wafer for energy dispersive X-ray spectroscopy (EDAX) 
by using Edward Coating Unit E-306. The surface mor-
phology of as-prepared samples was examined by means 
of JEOL JSM-6360LV, Japan, scanning electron micros-
copy (SEM). A Regaku X-ray diffractometer Ultima IV 
was employed for studying the structure of the material. 
The first order phase transformation in Ge25Se75 – xSbx 
glas-ses were investigated by using Differential Scan-
ning Calorimeter (Model–DSC plus, Rheometric Scien-
tific Company, U.K). The instrument was calibrated with 
indium, lead and tin standards. Each sample was hea-
ted at a constant heating rate of 5, 10, 15 and 20 K/min 
and the changes in heat flow with respect to tempera-
ture were measured. The glass transition temperature 
and the crystallization temperature were determined 
using the microprocessor of thermal analyzer. 
 
3. RESULTS AND DISCUSSION 
 
3.1 Structural Analysis 
 
Fig. 1 shows the energy dispersive X-ray spectros-
copy (EDAX) of Ge25Se63Sb12 thin films deposited on Si 
(100) substrate. The EDAX spectrum shows the peaks 
of Ge, Se, and Sb, thereby, confirming the presence of 
these elements in the samples. Thin films have been 
deposited on silicon wafer substrate and the silicon in 
the EDAX spectra shows very high intensity as com-
pared to Ge, Se and Sb. Therefore, the peaks corre-
sponding to Ge, Se and Sb are not much significant as 
compared to silicon peak, but the presence of all the 
elements have been observed as per our alloy composi-
tion. It is also observed that the composition obtained 
from EDAX analysis is almost same as that of starting 
composition of the as-prepared alloys. 
 
 
Fig. 1 – EDAX of Ge25Se63Sb12 thin films deposited on Si (100) 
wafer 
 
The surface morphology of Ge25Se60Sb15 powder was 
examined by means of JEOL JSM-6360LV, Japan, 
scanning electron microscopy (SEM), shown in Fig. 2, 
which confirms the amorphous state of the samples. 
 
 
 
Fig. 2 – SEM of as-prepared Ge25Se60Sb15 glasses 
 
A Regaku X-ray diffractometer Ultima IV was em-
ployed for studying the structure of the as-prepared and 
crystallized samples (collected from the DSC pans after 
completing the scan). 
Copper target was used as the X-ray source with 
  1.54178  Å (Cu K 1). The scanning angle was in the 
range of 10 -90 . A scan speed of 2 /min and a chart 
speed of 1 cm/min were maintained. The X-ray diffrac-
tion traces of all samples were taken at room tempera-
ture and found to show similar trends and hence only 
one of them is shown in Fig. 3a and b. 
The absence of sharp structural peak confirms the 
amorphous state of the samples while the presence of 
the sharp peaks confirms the crystalline nature of the 
samples. 
 
3.2 Glass Transition (Tg) and Crystallization (Tc) 
Temperature and Enthalpy Released 
 
Fig. 3 represents the DSC thermograms of 
Ge25Se69Sb6 glass recorded at different heating rates 5, 
10, 15 and 20 K/min. (Similar trends has also been ob-
served by other glassy systems bur are not shown here). 
 
 FIRST ORDER PHASE TRANSFORMATION IN… J. NANO- ELECTRON. PHYS. 5, 02021 (2013) 
 
 
02021-3 
 
 
 
 
Fig. 3 – X-ray pattern of Ge25Se66Sb9 sample (a) and X-ray 
pattern of crystallized Ge25Se60Sb15 sample (b) 
 
Two characteristic phenomena are evident in these 
DSC thermograms: (1) endothermic-like phenomenon 
indicating the glass transition region and (2) an exother-
mic phenomenon that manifest the crystallization process. 
The first order phase transformation in these glasses is 
characterized by measuring the glass transition (Tg) and 
crystallization temperature (Tc) with Sb contents and also 
the heating rates. The values of glass transition (Tg) and 
crystallization temperature (Tc) with Sb contents at the 
heating rate of 20 K/min are given in Table 1. It is clear 
from this table that Tg increases with increasing Sb con-
tents in the Ge-Se system. The increase in Tg could be 
attributed either to the increase in effective molecular 
weight with increasing Sb content or to the increase in 
concentration of long polymeric chains of Ge-Se. 
The Tg of a multi-component glass is known to be de-
pendent on several independent parameters such as 
band gap, co-ordination numbers, bond energy, effective 
molecular weight, the type and fraction of various struc-
tural units formed [24-26]. In our study Tg increases 
with increasing Sb concentration. Theoretically, Tg is 
defined as the temperature at which the relaxation time 
 becomes equal to the relaxation time of observation obs. 
At the same time, Tg varies inversely [27] as the relaxa-
tion time. With increasing Sb concentration, obs decreas-
es and hence the glass transition temperature increases. 
Both (Tc – Tg) and Tc represent the thermal stability 
of the glass. The values of (Tc – Tg) for different compo-
sitions are given in Table 1. It is clear from this table 
that (Tc – Tg) is highest for the composition of 6 % of Sb. 
Hence the glass with 6 % of Sb is most stable glass. 
The crystallization enthalpy Hc was evaluated for 
all composition using the formula 
 
 
Fig. 4 – DSC plot of Ge25Se69Sb6 glasses at different heating 
rates 5, 10, 15 and 20. 
 
 Hc  kA / m, (1) 
 
where k  1.5 is the constant of the instrument, A is the 
area of crystallization peak and m is the mass of sample. 
The enthalpy released is found to be less for 
Ge25Se69Sb6 glass which further confirms its maximum 
stability of this glass. 
 
3.3 Activation Energy of Crystallization ( Ec) 
 
The interpretation of the experimental crystalliza-
tion data is given on the basis of Kissinger’s, Matusita’s 
and modified Ozawa’s equations for non-isothermal 
crystallization. The activation energy ( Ec) for crystalli-
zation can therefore be calculated by using Kissinger’s 
equation [10-11], 
 
 ln (  / Tc2)  – Ec / RTc + D [4]  
 
The plot of ln (  / Tc2) versus 1000 / Tc for 
Ge25Se66Sb9 chalcogenide glasses are shown in Fig. 5, 
which come to be straight lines (similar trends has also 
been observed for other glasses and are not shown 
hear). The value of Ec may be calculated from the slope 
of each curve and is given in Table 1. 
The activation energy of crystallization increases with 
increasing Sb content in Ge-Se system, indicating that 
the rate of crystallization is faster as the Sb content 
increases. The increase in activation energy of crystalli-
zation may be interpreted in terms of increased hoping 
conduction in impurity induced states [28]. At higher 
concentration, alloying effect observed which could 
change the mobility gap and various other parameters 
of the original materials. The activation energy of crys-
tallization is an indication of the speed of rate of crys-
tallization. 
 
 F.A. AL-AGEL, F.M. AL-MARZOUKI, A.A. AL-GHAMDI, ET AL. J. NANO- ELECTRON. PHYS. 5, 02021 (2013) 
 
 
02021-4 
Table 1 – Compositional dependence of crystallization parameters Tc, Tg, (Tc – Tg), crystallization enthalpy ( Hc) and activation 
energy of crystallization ( Ec) of Ge25Se75 – xSbx from non-isothermal DSC experiments at a heating rate of 20 K/min 
 
Sample Tg (K) Tc (K) (Tc – Tg) (K) ( Hc) (J/mg) Ec (kJ/mole) 
Ge25Se69Sb6 323.25 389.19 65.94 1986.38 85.024 
Ge25Se66Sb9 327.34 384.16 56.82 2564.75 92.956 
Ge25Se63Sb12 331.21 379.46 48.25 3248.46 102.426 
Ge25Se60Sb15 336.44 372.13 35.69 4456.24 105.752 
 
 
 
 
Fig. 5 – Plot of ln (  / Tc2) as a function of 1000 / Tc (K) for 
Ga15Se85 – xAgx glass 
 
4. CONCLUSIONS 
 
Non-isothermal DSC measurements were performed 
to study the first order phase transformation in 
Ge25Se75 – xSbx chalcogenide glasses. It indicates that 
glass transition and crystallization temperatures de-
pend on the heating rate and on Sb concentration. The 
results of crystallization kinetics indicate that the de-
gree of crystallization under non-isothermal conditions 
fits well with the theory of Matusita, Sakka and Kissin-
ger. The temperature difference (Tc – Tg) and Tc is hig-
hest for the samples with 6 % of Sb. Hence, Ge25Se69Sb6 
glass is most stable. The enthalpy released is found to 
be less for Ge25Se69Sb6 glass which further confirms its 
maximum stability. The activation energy of crystalliza-
tion ( Ec) increases with increasing Sb contents in Ge-
Se system, which indicates that the speed of rate of 
crystallization is faster with increasing Sb concentra-
tion in the present system.  
 
ACKNOWLEDGMENT 
 
Thanks are due to King Abdulaziz City for Science 
and Technology (KACST), Riyadh, Saudi Arabia, (Grant 
No.: 10-ADV1412-03) for providing financial assistance 
in the form of National plan for Science and Technolo-
gies (major research project). Also thanks are extended 
to Deanship of Scientific Research (DSR) at King Ab-
dulaziz University (KAU), Jeddah, Saudi Arabia, for 
their systematic support.  
 
 
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First Order Phase Transformation in Amorphous Ge25Se75 – xSbx Glasses

Electronic Sumy State University Institutional Repository

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 5 No 2, 02021(4pp) (2013) Том 5 № 2, 02021(4cc) (2013)   2077-6772/2013/5(2)02021(4) 02021-1  2013 Sumy State University First Order Phase Transformation in Amorphous Ge25Se75 – xSbx Glasses  F.A. Al-Agel1, F.M. Al-Marzouki1, A.A. Al-Ghamdi1, Shamshad A. Khan2, E.A. Al-Arfaj3, M. Husain4  1 Department of Physics, King Abdulaziz University, Jeddah-21589, Saudi Arabia 2 Department of Physics, St. Andrew’s College, Gorakhpur, UP 273001, India 3 Department of Physics, College of Applied Sciences, Umm Al-Qura University, Makkah, Saudi Arabia 4 Department of Physics, Jamia Millia Islamia, New Delhi-110025, India  (Received 15 February 2013; revised manuscript received 06 May 2013; published online 07 May 2013)  Non-isothermal Differential scanning calorimetry (DSC) technique was used to study the kinetics of first order phase transformation in Ge25Se75 – xSbx glasses. The X-ray diffraction (XRD) technique was em-ployed to investigate the amorphous and crystalline phases in Ge25Se75 – xSbx glasses. From the heating rate dependences of crystallization temperature; the activation energy for crystallization and other kinetics pa-rameters were derived. The temperature difference (Tc – Tg) and Tc is highest for the samples with 6 % of Sb. Hence, Ge25Se69Sb6 glass is most stable. The enthalpy released is found to be less for Ge25Se69Sb6 glass which further confirms its maximum stability. The activation energy of crystallization ( Ec) is found to vary with compositions indicating a structural change due to the addition of Sb. The crystallization data are interpreted in terms of recent analyses developed for non-isothermal conditions. The present investiga-tion indicates that both the glass transition and the crystallization processes occur in a single stage.  Keywords: Glass transition temperature, Crystallization kinetics, X-Ray diffraction, Phase transformation.   PACS numbers: 71.55.Jv, 65.90. + I, 67.80.Gb, 73.61.Jc   1. INTRODUCTION  Amorphous chalcogenide glasses have been investi-gated extensively over the past few decades. These glasses have been widely used in device technology and the current interest in these materials centers on X-ray imaging and photonics [1]. The relevance of studying the phase transformation in these materials has a tech-nological aspect, since several physical properties change in the temperature range of utilization of the materials. It is also of fundamental scientific interest, since one can obtain useful information on the elemen-tary processes, which modify the structure of an amor-phous system, eventually producing stable phases on crystallization. The study the first order phase trans-formation in chalcogenide glasses by the differential scanning calorimetry (DSC) method has been widely discussed in literatures [2-8]. The first order phase sep-aration effects are of general interest in chalcogenide glasses. It is a term used to describe a phenomenon where an initially homogeneous system, such as a liq-uid, will unmix into two or more finely mixed chemically or structurally different, component or phases. Such structural effects produce usually pronounced changes in glass physical properties including a lowering of the glass transition temperature, a lowering of the optical band gap, an increase of molar volumes [9]. The phase transformation can exist on a variety of length scales from nanometers to micrometers or millimeters [9]. For the purpose of photonic applications, it is important that phase separation be eliminated or at least mini-mized to length scales much smaller than that the wavelengths of light being used. Apart from the tech-nical importance, the knowledge of crystallization kinet-ics is very important for a better understanding of amorphous structure of such chalcogenide glasses. The study of glass transition kinetics in chalcogenide glasses is of great importance to establish the thermal stability, glass-forming ability and ultimately to deter-mine the useful range of operating temperatures for a specific technological application before the eventual crystallization takes place. The glass forming tendency of the glassy alloys is related to ease by which melt can be cooled with the avoidance of crystal formation. Meanwhile, the thermal stability indicates the re-sistance of crystallization of glassy alloy through the nucleation and growth process. To evaluate the glass forming tendency and thermal stability of chalcogenide glasses, different simple quantitative methods are usu-ally used. The most commonly used methods are those suggested by Kissinger [10] and Ozawa [11], which are based on some characteristic temperatures such as the glass transition and crystallization temperatures moni-tored by the differential scanning calorimeter (DSC). The present work reports first order phase trans-formation in amorphous Ge25Se75 – xSbx glasses by using non-isothermal DSC measurements. The effect of varia-tion of Sb content on the thermal stability and glass forming tendency has also been studied. In the present system, we have used Se as a major content because it is widely used as a typical glass-former. The choice of selenium is due to its wide commercial importance. Its device applications like rectifiers, photocells and switch-ing memory, etc. have made it attractive. But the pure selenium has low sensitivity and short lifetime. In order to overcome this difficulty, several workers have used certain additives (Ga, Ge, Bi, etc.) for alloying Se to some extent. We have chosen germanium as an additive material. Germanium is also known to contribute to long-term room temperature stability [12]. We have incorporated Sb as the third element in Ge-Se alloys. The continued scientific interest in Sb based chalco-genide glasses is due to its potential use in phase change optical recording [13-18]. In phase change opti-cal recording, the recording of information is based on writing and erasing of amorphous marks in a crystalli-zation layer of a phase change material. Since the opti-cal properties of the amorphous phases are different from those of the crystallization phase, the written mark can be read out as a contrast in the reflectance. Besides sufficient optical contrast between the crystal-line and amorphous state, the thermal stability and  F.A. AL-AGEL, F.M. AL-MARZOUKI, A.A. AL-GHAMDI, ET AL. J. NANO- ELECTRON. PHYS. 5, 02021 (2013)   02021-2 glass forming tendency are one of the most important issues in developing phase change materials. In chalco-genide glasses, glass forming tendency and thermal ability of a glassy alloy is related to the ease by which melt can be cooled with the avoidance of crystal for-mation. The thermal stability and glass forming ten-dency play an important role in determining the utility of chalcogenide alloys as recording material [19-23]. The knowledge of the thermal stability and glass form-ing tendency in Ge25Se75 – xSbx glasses is, therefore, a subject of great interest.  2. EXPERIMENTAL DETAILS  Amorphous glassy alloys of Ge25Se75 – xSbx with x  6, 9 12 and 15 were prepared by melt quenching technique. The highly pure materials (99.999 % pure) were weighed according to their atomic percentages and sealed in quartz ampoules under a vacuum of 10 – 6 Torr using turbo pump. The sealed ampoules were then placed in a Microprocessor Controlled Programmable Muffle Fur-nace with rocking mechanism. The temperature of the furnace was increases at three stems. Initially at 773 K for 4 hours, then 973 K for 4 hours, and finally at 1273 K for 6 hours. The rocked motion accomplishes a complete mixing of the materials in the ampoule. Rapid quenching in ice-water bath was used to obtain the bulk amorphous material. By breaking the ampoule, ingots of the sample were taken out and then using ceramic tools the amor-phous material was crushed in to a fine powder.  Thin films of Ge25Se75 – xSbx glasses were prepared on Si (100) wafer for energy dispersive X-ray spectroscopy (EDAX) by using Edward Coating Unit E-306. The surface mor-phology of as-prepared samples was examined by means of JEOL JSM-6360LV, Japan, scanning electron micros-copy (SEM). A Regaku X-ray diffractometer Ultima IV was employed for studying the structure of the material. The first order phase transformation in Ge25Se75 – xSbx glas-ses were investigated by using Differential Scan-ning Calorimeter (Model–DSC plus, Rheometric Scien-tific Company, U.K). The instrument was calibrated with indium, lead and tin standards. Each sample was hea-ted at a constant heating rate of 5, 10, 15 and 20 K/min and the changes in heat flow with respect to tempera-ture were measured. The glass transition temperature and the crystallization temperature were determined using the microprocessor of thermal analyzer.  3. RESULTS AND DISCUSSION  3.1 Structural Analysis  Fig. 1 shows the energy dispersive X-ray spectros-copy (EDAX) of Ge25Se63Sb12 thin films deposited on Si (100) substrate. The EDAX spectrum shows the peaks of Ge, Se, and Sb, thereby, confirming the presence of these elements in the samples. Thin films have been deposited on silicon wafer substrate and the silicon in the EDAX spectra shows very high intensity as com-pared to Ge, Se and Sb. Therefore, the peaks corre-sponding to Ge, Se and Sb are not much significant as compared to silicon peak, but the presence of all the elements have been observed as per our alloy composi-tion. It is also observed that the composition obtained from EDAX analysis is almost same as that of starting composition of the as-prepared alloys.   Fig. 1 – EDAX of Ge25Se63Sb12 thin films deposited on Si (100) wafer  The surface morphology of Ge25Se60Sb15 powder was examined by means of JEOL JSM-6360LV, Japan, scanning electron microscopy (SEM), shown in Fig. 2, which confirms the amorphous state of the samples.    Fig. 2 – SEM of as-prepared Ge25Se60Sb15 glasses  A Regaku X-ray diffractometer Ultima IV was em-ployed for studying the structure of the as-prepared and crystallized samples (collected from the DSC pans after completing the scan). Copper target was used as the X-ray source with   1.54178  Å (Cu K 1). The scanning angle was in the range of 10 -90 . A scan speed of 2 /min and a chart speed of 1 cm/min were maintained. The X-ray diffrac-tion traces of all samples were taken at room tempera-ture and found to show similar trends and hence only one of them is shown in Fig. 3a and b. The absence of sharp structural peak confirms the amorphous state of the samples while the presence of the sharp peaks confirms the crystalline nature of the samples.  3.2 Glass Transition (Tg) and Crystallization (Tc) Temperature and Enthalpy Released  Fig. 3 represents the DSC thermograms of Ge25Se69Sb6 glass recorded at different heating rates 5, 10, 15 and 20 K/min. (Similar trends has also been ob-served by other glassy systems bur are not shown here).   FIRST ORDER PHASE TRANSFORMATION IN… J. NANO- ELECTRON. PHYS. 5, 02021 (2013)   02021-3     Fig. 3 – X-ray pattern of Ge25Se66Sb9 sample (a) and X-ray pattern of crystallized Ge25Se60Sb15 sample (b)  Two characteristic phenomena are evident in these DSC thermograms: (1) endothermic-like phenomenon indicating the glass transition region and (2) an exother-mic phenomenon that manifest the crystallization process. The first order phase transformation in these glasses is characterized by measuring the glass transition (Tg) and crystallization temperature (Tc) with Sb contents and also the heating rates. The values of glass transition (Tg) and crystallization temperature (Tc) with Sb contents at the heating rate of 20 K/min are given in Table 1. It is clear from this table that Tg increases with increasing Sb con-tents in the Ge-Se system. The increase in Tg could be attributed either to the increase in effective molecular weight with increasing Sb content or to the increase in concentration of long polymeric chains of Ge-Se. The Tg of a multi-component glass is known to be de-pendent on several independent parameters such as band gap, co-ordination numbers, bond energy, effective molecular weight, the type and fraction of various struc-tural units formed [24-26]. In our study Tg increases with increasing Sb concentration. Theoretically, Tg is defined as the temperature at which the relaxation time  becomes equal to the relaxation time of observation obs. At the same time, Tg varies inversely [27] as the relaxa-tion time. With increasing Sb concentration, obs decreas-es and hence the glass transition temperature increases. Both (Tc – Tg) and Tc represent the thermal stability of the glass. The values of (Tc – Tg) for different compo-sitions are given in Table 1. It is clear from this table that (Tc – Tg) is highest for the composition of 6 % of Sb. Hence the glass with 6 % of Sb is most stable glass. The crystallization enthalpy Hc was evaluated for all composition using the formula   Fig. 4 – DSC plot of Ge25Se69Sb6 glasses at different heating rates 5, 10, 15 and 20.   Hc  kA / m, (1)  where k  1.5 is the constant of the instrument, A is the area of crystallization peak and m is the mass of sample. The enthalpy released is found to be less for Ge25Se69Sb6 glass which further confirms its maximum stability of this glass.  3.3 Activation Energy of Crystallization ( Ec)  The interpretation of the experimental crystalliza-tion data is given on the basis of Kissinger’s, Matusita’s and modified Ozawa’s equations for non-isothermal crystallization. The activation energy ( Ec) for crystalli-zation can therefore be calculated by using Kissinger’s equation [10-11],   ln (  / Tc2)  – Ec / RTc + D [4]   The plot of ln (  / Tc2) versus 1000 / Tc for Ge25Se66Sb9 chalcogenide glasses are shown in Fig. 5, which come to be straight lines (similar trends has also been observed for other glasses and are not shown hear). The value of Ec may be calculated from the slope of each curve and is given in Table 1. The activation energy of crystallization increases with increasing Sb content in Ge-Se system, indicating that the rate of crystallization is faster as the Sb content increases. The increase in activation energy of crystalli-zation may be interpreted in terms of increased hoping conduction in impurity induced states [28]. At higher concentration, alloying effect observed which could change the mobility gap and various other parameters of the original materials. The activation energy of crys-tallization is an indication of the speed of rate of crys-tallization.   F.A. AL-AGEL, F.M. AL-MARZOUKI, A.A. AL-GHAMDI, ET AL. J. NANO- ELECTRON. PHYS. 5, 02021 (2013)   02021-4 Table 1 – Compositional dependence of crystallization parameters Tc, Tg, (Tc – Tg), crystallization enthalpy ( Hc) and activation energy of crystallization ( Ec) of Ge25Se75 – xSbx from non-isothermal DSC experiments at a heating rate of 20 K/min  Sample Tg (K) Tc (K) (Tc – Tg) (K) ( Hc) (J/mg) Ec (kJ/mole) Ge25Se69Sb6 323.25 389.19 65.94 1986.38 85.024 Ge25Se66Sb9 327.34 384.16 56.82 2564.75 92.956 Ge25Se63Sb12 331.21 379.46 48.25 3248.46 102.426 Ge25Se60Sb15 336.44 372.13 35.69 4456.24 105.752     Fig. 5 – Plot of ln (  / Tc2) as a function of 1000 / Tc (K) for Ga15Se85 – xAgx glass  4. CONCLUSIONS  Non-isothermal DSC measurements were performed to study the first order phase transformation in Ge25Se75 – xSbx chalcogenide glasses. It indicates that glass transition and crystallization temperatures de-pend on the heating rate and on Sb concentration. The results of crystallization kinetics indicate that the de-gree of crystallization under non-isothermal conditions fits well with the theory of Matusita, Sakka and Kissin-ger. The temperature difference (Tc – Tg) and Tc is hig-hest for the samples with 6 % of Sb. Hence, Ge25Se69Sb6 glass is most stable. The enthalpy released is found to be less for Ge25Se69Sb6 glass which further confirms its maximum stability. The activation energy of crystalliza-tion ( Ec) increases with increasing Sb contents in Ge-Se system, which indicates that the speed of rate of crystallization is faster with increasing Sb concentra-tion in the present system.   ACKNOWLEDGMENT  Thanks are due to King Abdulaziz City for Science and Technology (KACST), Riyadh, Saudi Arabia, (Grant No.: 10-ADV1412-03) for providing financial assistance in the form of National plan for Science and Technolo-gies (major research project). Also thanks are extended to Deanship of Scientific Research (DSR) at King Ab-dulaziz University (KAU), Jeddah, Saudi Arabia, for their systematic support.    REFERENCES  1. J. Rowlands, S. Kasap, Phys. Today 50, 24 (1997). 2. Shamshad A. Khan, J.K. Lal, F.A. Al-Agel, M.A. Alvi,  J. Alloy. Compd. 554, 227 (2013). 3. Abhay K. Singh, J. Alloy. Compd. 552, 166 (2013). 4. Mostafa I. Abd-Elrahman, Mohmmed M. Hafiz, Physica B 410, 53 (2013). 5. Jili Wu, Ye Pan, Jindu Huang, Jinhong Pi, Thermochim. Acta 552, 15 (2013). 6. K.D. Machado, C.M. Poffo, J.C. de Lima, S.M. de Souza, Solid State Commun. 152, 1604 (2012). 7. Praveen Kumar, S.N. Yannopoulos, T.S. Sathiaraj, R. Thangaraj, Mater. Chem. Phys. 135, 68 (2012). 8. A.M. Shakra, S.A. 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First Order Phase Transformation in Amorphous Ge25Se75 – xSbx Glasses

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