Effect of Ag addition on the a.c. conductivity as a function of frequency in Se80.5Bi1.5Te18 – yAgy (y  1.0, 1.5 and 2.0 at. %) glassy alloy has been investigated in the temperature range 300-355 K. The electrical conductivity is measured as a function of frequency () of an alternating electric field in the frequency range 1 -500 kHz, using Wayne Kerr 6500 B Impedance Analyzer. A.C. conductivity (ω) is found to increases with an increase in frequency for the entire range of temperature in all compositions. The frequency exponent s is found to decrease with an increase in temperature which indicates that the correlated barrier hopping is the possible conduction mechanism in the investigated samples.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3101

Heera, Pawan

Kumar, Anup

Sharma, Raman

Electronic Sumy State University Institutional Repository

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 5 No 2, 02020(5pp) (2013) Том 5 № 2, 02020(5cc) (2013)   2077-6772/2013/5(2)02020(5) 02020-1  2013 Sumy State University A.C. Conductivity of Ag Incorporated Se-Te-Bi Glassy Alloy   Anup Kumar1,2,*, Pawan Heera1, Raman Sharma1,†  1 Department of Physics, Himachal Pradesh University, Shimla-5, India 2 Physics Department, P. G. Govt. Degree College, Kullu, H. P., India  (Received 15 February 2013; published online 04 May 2013)  Effect of Ag addition on the a.c. conductivity as a function of frequency in Se80.5Bi1.5Te18 – yAgy (y  1.0, 1.5 and 2.0 at. %) glassy alloy has been investigated in the temperature range 300-355 K. The electrical conductivity is measured as a function of frequency ( ) of an alternating electric field in the frequency range 1 -500 kHz, using Wayne Kerr 6500 B Impedance Analyzer. A.C. conductivity (ω) is found to in-creases with an increase in frequency for the entire range of temperature in all compositions. The frequen-cy exponent s is found to decrease with an increase in temperature which indicates that the correlated bar-rier hopping is the possible conduction mechanism in the investigated samples.  Keywords: A.C. conductivity, Chalcogenide glasses, Activation energy, Frequency exponent.   PACS numbers: 61.43Dq, 81.05Gc, 81.05Kf                                                                   * kumar.anup.sml@gmail.com  † sramanb70@mailcity.com 1. INTRODUCTION  Multinary amorphous semiconducting materials are the subject of growing interest because they contain the characteristic features of disordered materials and some properties of crystalline semiconducting materials. These chalcogenide semiconductors possesses fast, accu-rate, low cost and quality device applications [1, 2]. They have been proposed [3-6] for prospective applica-tions in photoelectronics, solid-state electrolytes for lith-ium secondary batteries and thermoelectric devices. These materials have numerous applications in optical memories, optical coating such as imaging, display, communication, sensing, manufacturing of anti reflec-tion coating and filters [7-9] etc. The properties of chal-cogenide glasses which depend on chemical composition are of special interest in considering the effect of aver-age coordination number and the number of covalent bonds per atom [10]. The effect of impurity atoms in chalcogenide glasses depends upon the chemical nature of impurity, composition of the glass and the value of impurity concentration. The nature of defect centers in these glasses is supposed to be responsible [11] for the type of conduction mechanism in these materials. The chalcogenide glasses shows p-type conduction [12] based on the asymmetry of conduction and valance band. The disorder has larger effect on antibonding states than on non-bonding states which results in a deeper tail for the conduction band. However, the conductivity of chalco-genide glasses switches from p to n type due to the addi-tion of Bi in Se-Te system [12-14]. From application point of view it will be useful to study the affect of metal impurities on the properties of Se-Te glasses. The addi-tion of an impurity like Bi, Sn, Sb, Ag, etc. to this alloy is found to improve its various properties like higher glass transition temperature, higher crystallization temperature and thermal stability [15-17]. The optical and electrical data available suggest that the addition of Bi produces localized states near the conduction band edge so the electrical properties are influenced by the hopping of electron in the localized states at the conduc-tion band edge. It is found that Ag diffuses easily in the chalcogenide system by bridging the chalcogenide chains and makes the system stable [18]. Addition of Ag results in various structural changes in the materials which in turn modify the band structure and hence elec-trical properties due to its ionic nature. Ag containing chalcogenide glasses have attracted much attention in glass science and technology due to their potential de-vice applications in chemistry, optoelectronics, biology and in optics [19-21]. They can be used as optical memory, holography and membranes of sensors for po-tentiometric determination [19, 22-24]. In the present work we aim to study the effect of Ag on the electrical properties, especially, the a.c. conduc-tivity of Se-Te-Bi semiconducting glassy alloys and to highlight some new features of these chalcogenide ma-terials for their applications. The frequency and tem-perature dependence of A.C. conductivity is studied in the frequency range 1-500 kHz over the temperature range 300-355 K, using parallel impedance measure-ments. The A.C. conductivity (ω) as a function of fre-quency, at different temperatures, is found to increases with an increase in frequency whereas the frequency exponent s is found to decrease with an increase in tem-perature for all compositions. The correlated barrier hopping (CBH) model has been used to describe the temperature dependence of A.C. conductivity and the frequency exponent s.  2. EXPERIMENTAL DETAILS  The glassy alloys of Se80.5Bi1.5Te18 – yAgy (y  0, 1.0, 1.5 and 2.0 at. %) in bulk form were prepared by melt quenching technique. High purity (99.999 %) elemental substances were weighed according to their atomic per-centages and were sealed in quartz ampoules evacuat-ed to a vacuum of 10 – 5 Torr. The sealed ampoules were heated in a vertical furnace at an appropriate tempera-ture of 1323 K for 15 hours by gradually increasing the  ANUP KUMAR, PAWAN HEERA, RAMAN SHARMA J. NANO- ELECTRON. PHYS. 5, 02020 (2013)   02020-2 temperature at the rate of 3-4 K min – 1. The ampoules were rocked frequently during heating in order to en-sure homogenization of the melt. The ampoules were quenched in ice cooled water to obtain the glassy alloy. The samples were taken out from the ampoules by dis-solving the ampoules in HF + H2O2 solution for about 48 h. The amorphous state of the bulk samples was confirmed by X-ray diffraction as no prominent peak was observed in the spectra. The glassy alloy so pre-pared was grinded to a fine powder and the samples in the form of pellets of diameter about 10 mm and thick-ness between 1-2 mm were prepared by compressing the powder in a good quality steel die under a load of 5 tons. The pallets were coated, both sides, with air drying conducting silver paste in order to obtain the good quality contact with the electrodes of the sample holder. The coated pellets were mounted between two steel electrodes inside a specially designed sample holder which is connected to Wayne Kerr 6500 B Im-pedance Analyzer. To determine the a.c. conductivity of Se80.5Bi1.5Te18 – yAgy alloys the impedance parameter Z and conductance G were measured in the frequency range 1 to 500 kHz at different temperatures ranging from 300 to 355 K. All the measurements are done in vacuum so as to avoid the effect of moisture on the die-lectric properties. The measurements were done under identical experimental conditions for all the samples so that the results could be compared.  3. RESULTS AND DISCUSSION  In general, total measured conductivity at a given frequency, consisting of D.C. and A.C. components, can expressed as   . .( ) ( )Total DC  (1)  The A.C. conductivity ( ), can be calculated by measuring total conductivity at a given frequency and then subtracting D.C. conductivity from it. In chalco-genide glasses the D.C. conductivity arises due to the band conduction by carriers in extended states beyond the mobility edge and ( ) arises due to the relaxation processes. If both D.C. and A.C. conduction are taking place then D.C. is simply given by    . .0lim ( )D C t  (2)  ( ) in amorphous semiconductors increase monoto-nically with frequency and usually depends on temper-ature. The pure A.C. component of conductivity tends to dominate at high frequency or at low temperature. Generally, all amorphous semi-conductors exhibit fre-quency dependence of conductivity which increases almost linearly with frequency in a given range 102    108 sec – 1.  3.1 Frequency Dependence of A.C. Conductivity  The frequency dependence of A.C. conductivity in semiconductors and some disordered systems is ex-pected due to the conduction in localized states [27]. The low temperature A.C. conduction can be explained by considering bipolaron hopping between D + and D −    Fig. 1 – Variation of ln( ) versus ln(ω) for Se80.5Bi1.5Te18 glass at different temperatures    Fig. 2 – Variation of ln( ) versus ln(ω) for Se80.5Bi1.5Te17Ag1 glass at different temperatures  centers whereas the higher temperature behavior is due to thermally activated single polaron hopping. At higher temperatures a number of thermally gen-erated D0 centers are produced with a temperature de-pendent concentration [28]. The A.C. conductivity, (ω), in these materials is found to obey the relation.   . .( )SA C A , (3)  In equation (6) s (≤ 1) is a frequency exponent and is given [29] as   . .(ln ( )) 61lnA C Bmd k Tsd W. (4)  Here, Wm is the maximum barrier height over which the electron hop, T is the absolute temperature and kB is the Boltzmann constant.  The plots of the A.C. conductivity A.C.(ω)  as a func-tion of frequency for the investigated compositions, at different temperatures, are shown in Fig. 1-4. Fig. 1-4 reveals that (ω) increases with an increase in frequen-cy at different temperatures.  A.C. CONDUCTIVITY OF AG INCORPORATED SE-TE-BI GLASSY ALLOY … J. NANO- ELECTRON. PHYS. 5, 02020 (2013)   02020-3   Fig. 3 – Variation of ln( ) versus ln(ω) for Se80.5Bi1.5Te16.5Ag1.5 glasses at different temperatures    Fig. 4 – Variation of ln( ) versus ln(ω) for Se80.5Bi1.5Te16Ag2 glass at different temperatures  The values of frequency exponent s is calculated from the slope of the curves plotted between ln A.C.(ω) and ln(ω). The mean value of the frequency exponent for all compositions is plotted as a function of tempera-ture in Fig. 5. From Fig. 5 it evident that s lies between 0.20 to 0.75 and decrease with an increase in tempera-ture. Our results for s are in agreement with the earlier reported results for other chalcogenide glasses [27, 29-33]. The variation of s with temperature indicates that the correlated barrier hopping (CBH) is the possible conduction mechanism in the investigated samples [28]. According to CBH model, the values of frequency exponent s should decreases with increase in tempera-ture. Hence, our results show that the conduction mechanism in the system under study can be explained in terms CBH model.  3.2 Temperature Dependence of A.C. Conducti-vity and Activation Energy of Conduction  The temperature dependence of A.C. conductivity (ω) for Se80.5Bi1.5Te18 – yAgy (y  0, 1.0, 1.5 and 2.0) glasses is studied in the temperature range  of 300 to   Fig. 5 – Variation of s with Temperature (K) for  Se80.5Bi1.5Te18 – yAgy (y  0, 1.0, 1.5 and 2.0) glasses  355 K at different frequencies. The obtained A.C. con-ductivity (ω) as a function of temperature for different compositions is plotted in Fig. 6-9. Fig. 6–9, show that A.C. conductivity increases with an increase in tempera-ture as well as with frequency for all compositions. This shows that the A.C. conductivity is a thermally activated process from different localized states in the gap or its tail. Our results for temperature dependence of A.C. conductivity are in agreement with the results reported for other amorphous materials [29, 34-35]. The composi-tional variation of (ω) as a function of temperature at a frequency of 1 kHz is shown in Fig. 10.    Fig. 6 – Variation of ln A.C.(ω) versus 1000 / T at different frequencies for Se80.5Bi1.5Te18 glass  The A.C. activation energy of conduction for Se80.5Bi1.5Te18 – yAgy glasses is calculated from the slopes of plots of ln A.C.(ω) versus 1000 / T by using well known relation [32]   . .0( )( ) ( )exp A CEkT (5)   ANUP KUMAR, PAWAN HEERA, RAMAN SHARMA J. NANO- ELECTRON. PHYS. 5, 02020 (2013)   02020-4   Fig. 7 – Variation of ln A.C.(ω) versus 1000 / T at different frequencies for Se80.5Bi1.5Te17Ag1 glass    Fig. 8 – Variation of ln A.C.(ω) versus 1000 / T at different frequencies for Se80.5Bi1.5Te16.5Ag1.5 glass    Fig. 9 – Variation of ln A.C.(ω) versus 1000 / T at different frequencies for Se80.5Bi1.5Te16Ag2  glass    Fig. 10 – Variation of ln A.C. with temperature 1000 / T in Se80.5Bi1.5Te18 – yAgy glasses at 1 kHz  Table 1 – Values of activation energy ΔEA.C.(ω) at different frequencies for Se80.5Bi1.5Te18 – yAgy glasses  Frequency ΔEA.C.(ω) Se80.5Bi1.5Te18 Se80.5Bi1.5Te17Ag1 Se80.5Bi1.5Te16.5Ag1.5 Se80.5Bi1.5Te16Ag2 50 Hz 3.37234 3.29806 2.97486 1.36003 100 Hz 2.94961 3.22515 2.95997 1.3584 500 Hz 2.0437 2.85743 2.79491 1.33799 1 KHz 1.61295 2.53763 2.64512 1.31188 10 KHz 0.56483 1.17601 1.63319 1.07895 50 KHz 0.2464 0.53787 0.79083 0.72308 100 KHz 0.17217 0.36606 0.53681 0.53233 500 KHz 0.08137 0.13485 0.19615 0.22927  here ΔEA.C.(ω) is the A.C. activation energy and 0(ω) is the pre exponential factor. The values of activation energy ΔEA.C.(ω) at different frequencies are reported in the Table 1. It is found that a.c. activation energy ΔEA.C.(ω) de-creases with an increase in frequency which is in accor-dance with the earlier results [27, 36]. This decrease may be attributed to the increase in applied field frequency, which enhances the electronic jump between localized states. The obtained results of A.C. activation energy for the samples support the hopping conduction mechanism.   A.C. CONDUCTIVITY OF AG INCORPORATED SE-TE-BI GLASSY ALLOY … J. NANO- ELECTRON. PHYS. 5, 02020 (2013)   02020-5 4. CONCLUSIONS  The effect of Ag incorporation on the A.C. conductivity has been  studied in Se80.5Bi1.5Te18 – yAgy (y  0, 1.0, 1.5 and 2.0) alloys in the frequency range 1-500 kHz over the temperature range 300-355 K, using parallel impedance measurements. The temperature dependence of A.C. conductivity and the exponent s are discussed in terms of the correlated barrier hopping (CBH) model which indi-cates that A.C. conductivity ( ) is proportional to s, s < 1 and decreases with increasing temperature.  A.C. conductivity (ω) as a function of frequency, at different temperatures, is found to increases with an  increase in frequency for all compositions. The frequency exponent s is found to decrease with an increase in tem-perature which indicates that the correlated barrier hopping is the possible conduction mechanism in the investigated samples. The frequency dependence of A.C. conductivity and temperature dependence of s (frequen-cy exponent) show that these glasses exhibit the hopping conduction type mechanism. Hence, correlated barrier hopping (CBH) model may be employed to describe the conduction mechanism in the investigated compositions.  ACKNOWLEDGEMENT  One of the authors is very grateful to Dr. Dhaneshwari Sharma for her valuable and kind co-operation during this work.    REFERENCES  1. I.S. Yahia, N.A. Hegab, A.M. Shakra, A.M. Al-Ribaty, Physica B 407, 2476 (2012). 2. M.A. Majeed, M. Julfequar, A. Kumar, M. Husain,  Mater. Chem. Phys. 87, 179 (2004). 3. N. Kushwaha, V.S. Kushwaha, R.K. Shukla, A. Kumar,  J. Non-Cryst. Solids 351, 3414 (2005). 4. A.K. Singh, J. Non-Oxide Glasses 3 No 1, 1 (2012). 5. R. Chander, R. Thangaraj, Appl. Phys. A: Mater. 99, 181 (2010). 6. Deepika, P.K. Jain, K.S. Rahtore, N. Saxena, J. Non-Cryst. Solids 355, 1274 (2009). 7. M. Ahmad, R. Thangaraj, T.S.Sathiaraj, J. Mater Sci. 45, 1231 (2010). 8. M.A. Popesco, Non Crystalline Chalcogenides (Kluwer: Dordrecht: 2000). 9. A. Zakery, S.R. Elliott, J. Non-Cryst. Solids 330, 1 (2003). 10. E. Skordeva, D. Arsova, J. Non-Cryst. Solids 192-193, 665 (1995). 11. N. Chandel, N. Mehta, A. Kumar, Curr. Appl. Phys. 12, 405 (2012). 12. S. D. Baranovski, Semiconductors 18, 633 (1984). 13. D.R. Macfarlane, M. Matecki, M. Poulain, J. Non-Cryst. Solids 64, 351 (1984). 14. V.S. Shiryaev, J.L. Adam, X.H. Zhang, J. Phys. Chem. Solids 65, 1737 (2004). 15. B. Li, Y. Xie, Y. Xu, C. Wu, Z. Li, J. Solid State Chem. 179, 56 (2006). 16. A. Sharma, P.B. Barman, J. Therm. Anal. Calorim. 96, 413 (2009). 17. M. Hrdlicka, J. Prikryl, M. Pavlista, L. Benes, M. Vlcek, F. Frumara, J. Phys. Chem. Solids 68, 846 (2007). 18. N. Toghe, Y. Yamamoto, T. Minami, M. Tanka, Appl. Phys. Lett. 34, 640 (1979). 19. M. Mitkova, Z. Boncheva-Mladenova, Monatshefte Für Chemie 120, 643 (1989). 20. M. Frumar, T. Wagner, Curr. Opin. Solid State Mater. Sci. 7, 117 (2003). 21. J.M.C. Garrido, F. Macoretta, M.A. Urena, B. Arcondo,  J. Non-Cryst. Solids 355, 2079 (2009). 22. A.A. Piarristeguy, G.J. Cuello, B. Arcondo, A. Pradel, M. Ribes, J. Non-Cryst. Solids 353, 1243 (2007). 23. J. Schubert, et al., Sensor. Actuat. B: Chem. 76, 327 (2001). 24. A.A. Al-Ghamdi, M.A. Alvi, S.A. Khan, J. Alloy. Compd. 509, 2087 (2011). 25. M. Pollok, T.H. Gebelle, Phys. Rev. 122, 1942 (1961). 26. Z.U. Borisova, Glassy Semiconductors (New York: Plenum: 1981). 27. J. Sharma, S. Kumar, Physica B 407, 457 (2012). 28. S.R. Elliott, Adv. Phys. 36, 135 (1987). 29. I.S. Yahia, N.A. Hegab, A.M. Shakra, A.M. AL-Ribaty, Physica B 407, 2476 (2012). 30. N. Chandel, N. Mehta, A. Kumar, Curr. Appl. Phys. 12, 405 (2012). 31. F.A. Abdel Wahab, M. Abdel-Baki, J. Non-Cryst. Solids 355, 2239 (2009). 32. A.E. Bekheet, N.A. Hegab, Vacuum 83, 391 (2009). 33. G. Singh, N. Goyal, G.S.S. Saini, S.K. Tripathi, J. Non-Cryst. Solids 353, 1322 (2007). 34. N.A. Hegab, M.A. Afifi, H.E. Atyia, M.I. Ismael, Acta Physica Pol. A 119 No 3, 416 (2011). 35. A.M. Farid, H.E. Atyia, N.A. Hegab, Vacuum 80, 284 (2005). 36. C.A. Angell, Annu. Rev. Phys. Chem. 43, 693 (1992).  

A.C. Conductivity of Ag Incorporated Se-Te-Bi Glassy Alloy

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 5 No 2, 02020(5pp) (2013) Том 5 № 2, 02020(5cc) (2013) 
 
 
2077-6772/2013/5(2)02020(5) 02020-1  2013 Sumy State University 
A.C. Conductivity of Ag Incorporated Se-Te-Bi Glassy Alloy  
 
Anup Kumar1,2,*, Pawan Heera1, Raman Sharma1,† 
 
1 Department of Physics, Himachal Pradesh University, Shimla-5, India 
2 Physics Department, P. G. Govt. Degree College, Kullu, H. P., India 
 
(Received 15 February 2013; published online 04 May 2013) 
 
Effect of Ag addition on the a.c. conductivity as a function of frequency in Se80.5Bi1.5Te18 – yAgy (y  1.0, 
1.5 and 2.0 at. %) glassy alloy has been investigated in the temperature range 300-355 K. The electrical 
conductivity is measured as a function of frequency ( ) of an alternating electric field in the frequency 
range 1 -500 kHz, using Wayne Kerr 6500 B Impedance Analyzer. A.C. conductivity (ω) is found to in-
creases with an increase in frequency for the entire range of temperature in all compositions. The frequen-
cy exponent s is found to decrease with an increase in temperature which indicates that the correlated bar-
rier hopping is the possible conduction mechanism in the investigated samples. 
 
Keywords: A.C. conductivity, Chalcogenide glasses, Activation energy, Frequency exponent. 
 
 PACS numbers: 61.43Dq, 81.05Gc, 81.05Kf 
 
 
                                                                
* kumar.anup.sml@gmail.com  
† sramanb70@mailcity.com 
1. INTRODUCTION 
 
Multinary amorphous semiconducting materials are 
the subject of growing interest because they contain the 
characteristic features of disordered materials and some 
properties of crystalline semiconducting materials. 
These chalcogenide semiconductors possesses fast, accu-
rate, low cost and quality device applications [1, 2]. 
They have been proposed [3-6] for prospective applica-
tions in photoelectronics, solid-state electrolytes for lith-
ium secondary batteries and thermoelectric devices. 
These materials have numerous applications in optical 
memories, optical coating such as imaging, display, 
communication, sensing, manufacturing of anti reflec-
tion coating and filters [7-9] etc. The properties of chal-
cogenide glasses which depend on chemical composition 
are of special interest in considering the effect of aver-
age coordination number and the number of covalent 
bonds per atom [10]. The effect of impurity atoms in 
chalcogenide glasses depends upon the chemical nature 
of impurity, composition of the glass and the value of 
impurity concentration. The nature of defect centers in 
these glasses is supposed to be responsible [11] for the 
type of conduction mechanism in these materials. The 
chalcogenide glasses shows p-type conduction [12] based 
on the asymmetry of conduction and valance band. The 
disorder has larger effect on antibonding states than on 
non-bonding states which results in a deeper tail for the 
conduction band. However, the conductivity of chalco-
genide glasses switches from p to n type due to the addi-
tion of Bi in Se-Te system [12-14]. From application 
point of view it will be useful to study the affect of metal 
impurities on the properties of Se-Te glasses. The addi-
tion of an impurity like Bi, Sn, Sb, Ag, etc. to this alloy 
is found to improve its various properties like higher 
glass transition temperature, higher crystallization 
temperature and thermal stability [15-17]. The optical 
and electrical data available suggest that the addition of 
Bi produces localized states near the conduction band 
edge so the electrical properties are influenced by the 
hopping of electron in the localized states at the conduc-
tion band edge. It is found that Ag diffuses easily in the 
chalcogenide system by bridging the chalcogenide 
chains and makes the system stable [18]. Addition of Ag 
results in various structural changes in the materials 
which in turn modify the band structure and hence elec-
trical properties due to its ionic nature. Ag containing 
chalcogenide glasses have attracted much attention in 
glass science and technology due to their potential de-
vice applications in chemistry, optoelectronics, biology 
and in optics [19-21]. They can be used as optical 
memory, holography and membranes of sensors for po-
tentiometric determination [19, 22-24]. 
In the present work we aim to study the effect of Ag 
on the electrical properties, especially, the a.c. conduc-
tivity of Se-Te-Bi semiconducting glassy alloys and to 
highlight some new features of these chalcogenide ma-
terials for their applications. The frequency and tem-
perature dependence of A.C. conductivity is studied in 
the frequency range 1-500 kHz over the temperature 
range 300-355 K, using parallel impedance measure-
ments. The A.C. conductivity (ω) as a function of fre-
quency, at different temperatures, is found to increases 
with an increase in frequency whereas the frequency 
exponent s is found to decrease with an increase in tem-
perature for all compositions. The correlated barrier 
hopping (CBH) model has been used to describe the 
temperature dependence of A.C. conductivity and the 
frequency exponent s. 
 
2. EXPERIMENTAL DETAILS 
 
The glassy alloys of Se80.5Bi1.5Te18 – yAgy (y  0, 1.0, 
1.5 and 2.0 at. %) in bulk form were prepared by melt 
quenching technique. High purity (99.999 %) elemental 
substances were weighed according to their atomic per-
centages and were sealed in quartz ampoules evacuat-
ed to a vacuum of 10 – 5 Torr. The sealed ampoules were 
heated in a vertical furnace at an appropriate tempera-
ture of 1323 K for 15 hours by gradually increasing the 
 ANUP KUMAR, PAWAN HEERA, RAMAN SHARMA J. NANO- ELECTRON. PHYS. 5, 02020 (2013) 
 
 
02020-2 
temperature at the rate of 3-4 K min – 1. The ampoules 
were rocked frequently during heating in order to en-
sure homogenization of the melt. The ampoules were 
quenched in ice cooled water to obtain the glassy alloy. 
The samples were taken out from the ampoules by dis-
solving the ampoules in HF + H2O2 solution for about 
48 h. The amorphous state of the bulk samples was 
confirmed by X-ray diffraction as no prominent peak 
was observed in the spectra. The glassy alloy so pre-
pared was grinded to a fine powder and the samples in 
the form of pellets of diameter about 10 mm and thick-
ness between 1-2 mm were prepared by compressing 
the powder in a good quality steel die under a load of 
5 tons. The pallets were coated, both sides, with air 
drying conducting silver paste in order to obtain the 
good quality contact with the electrodes of the sample 
holder. The coated pellets were mounted between two 
steel electrodes inside a specially designed sample 
holder which is connected to Wayne Kerr 6500 B Im-
pedance Analyzer. To determine the a.c. conductivity of 
Se80.5Bi1.5Te18 – yAgy alloys the impedance parameter Z 
and conductance G were measured in the frequency 
range 1 to 500 kHz at different temperatures ranging 
from 300 to 355 K. All the measurements are done in 
vacuum so as to avoid the effect of moisture on the die-
lectric properties. The measurements were done under 
identical experimental conditions for all the samples so 
that the results could be compared. 
 
3. RESULTS AND DISCUSSION 
 
In general, total measured conductivity at a given 
frequency, consisting of D.C. and A.C. components, can 
expressed as 
 
 
. .( ) ( )Total DC  (1) 
 
The A.C. conductivity ( ), can be calculated by 
measuring total conductivity at a given frequency and 
then subtracting D.C. conductivity from it. In chalco-
genide glasses the D.C. conductivity arises due to the 
band conduction by carriers in extended states beyond 
the mobility edge and ( ) arises due to the relaxation 
processes. If both D.C. and A.C. conduction are taking 
place then D.C. is simply given by  
 
 . .
0
lim ( )D C t  (2) 
 
( ) in amorphous semiconductors increase monoto-
nically with frequency and usually depends on temper-
ature. The pure A.C. component of conductivity tends 
to dominate at high frequency or at low temperature. 
Generally, all amorphous semi-conductors exhibit fre-
quency dependence of conductivity which increases 
almost linearly with frequency in a given range 
102    108 sec – 1. 
 
3.1 Frequency Dependence of A.C. Conductivity 
 
The frequency dependence of A.C. conductivity in 
semiconductors and some disordered systems is ex-
pected due to the conduction in localized states [27]. 
The low temperature A.C. conduction can be explained 
by considering bipolaron hopping between D + and D −  
 
 
Fig. 1 – Variation of ln( ) versus ln(ω) for Se80.5Bi1.5Te18 glass 
at different temperatures 
 
 
 
Fig. 2 – Variation of ln( ) versus ln(ω) for Se80.5Bi1.5Te17Ag1 
glass at different temperatures 
 
centers whereas the higher temperature behavior is 
due to thermally activated single polaron hopping. 
At higher temperatures a number of thermally gen-
erated D0 centers are produced with a temperature de-
pendent concentration [28]. The A.C. conductivity, (ω), 
in these materials is found to obey the relation. 
 
 . .( )
S
A C A , (3) 
 
In equation (6) s (≤ 1) is a frequency exponent and is 
given [29] as 
 
 . .
(ln ( )) 6
1
ln
A C B
m
d k T
s
d W
. (4) 
 
Here, Wm is the maximum barrier height over which 
the electron hop, T is the absolute temperature and kB 
is the Boltzmann constant.  
The plots of the A.C. conductivity A.C.(ω)  as a func-
tion of frequency for the investigated compositions, at 
different temperatures, are shown in Fig. 1-4. Fig. 1-4 
reveals that (ω) increases with an increase in frequen-
cy at different temperatures. 
 A.C. CONDUCTIVITY OF AG INCORPORATED SE-TE-BI GLASSY ALLOY … J. NANO- ELECTRON. PHYS. 5, 02020 (2013) 
 
 
02020-3 
 
 
Fig. 3 – Variation of ln( ) versus ln(ω) for Se80.5Bi1.5Te16.5Ag1.5 
glasses at different temperatures 
 
 
 
Fig. 4 – Variation of ln( ) versus ln(ω) for Se80.5Bi1.5Te16Ag2 
glass at different temperatures 
 
The values of frequency exponent s is calculated 
from the slope of the curves plotted between ln A.C.(ω) 
and ln(ω). The mean value of the frequency exponent 
for all compositions is plotted as a function of tempera-
ture in Fig. 5. From Fig. 5 it evident that s lies between 
0.20 to 0.75 and decrease with an increase in tempera-
ture. Our results for s are in agreement with the earlier 
reported results for other chalcogenide glasses [27, 29-
33]. The variation of s with temperature indicates that 
the correlated barrier hopping (CBH) is the possible 
conduction mechanism in the investigated samples 
[28]. According to CBH model, the values of frequency 
exponent s should decreases with increase in tempera-
ture. Hence, our results show that the conduction 
mechanism in the system under study can be explained 
in terms CBH model. 
 
3.2 Temperature Dependence of A.C. Conducti-
vity and Activation Energy of Conduction 
 
The temperature dependence of A.C. conductivity 
(ω) for Se80.5Bi1.5Te18 – yAgy (y  0, 1.0, 1.5 and 2.0) 
glasses is studied in the temperature range  of 300 to 
 
 
Fig. 5 – Variation of s with Temperature (K) for  
Se80.5Bi1.5Te18 – yAgy (y  0, 1.0, 1.5 and 2.0) glasses 
 
355 K at different frequencies. The obtained A.C. con-
ductivity (ω) as a function of temperature for different 
compositions is plotted in Fig. 6-9. Fig. 6–9, show that 
A.C. conductivity increases with an increase in tempera-
ture as well as with frequency for all compositions. This 
shows that the A.C. conductivity is a thermally activated 
process from different localized states in the gap or its 
tail. Our results for temperature dependence of A.C. 
conductivity are in agreement with the results reported 
for other amorphous materials [29, 34-35]. The composi-
tional variation of (ω) as a function of temperature at a 
frequency of 1 kHz is shown in Fig. 10. 
 
 
 
Fig. 6 – Variation of ln A.C.(ω) versus 1000 / T at different 
frequencies for Se80.5Bi1.5Te18 glass 
 
The A.C. activation energy of conduction for 
Se80.5Bi1.5Te18 – yAgy glasses is calculated from the slopes 
of plots of ln A.C.(ω) versus 1000 / T by using well 
known relation [32] 
 
 . .0
( )
( ) ( )exp A C
E
kT
 (5) 
 
 ANUP KUMAR, PAWAN HEERA, RAMAN SHARMA J. NANO- ELECTRON. PHYS. 5, 02020 (2013) 
 
 
02020-4 
 
 
Fig. 7 – Variation of ln A.C.(ω) versus 1000 / T at different 
frequencies for Se80.5Bi1.5Te17Ag1 glass 
 
 
 
Fig. 8 – Variation of ln A.C.(ω) versus 1000 / T at different 
frequencies for Se80.5Bi1.5Te16.5Ag1.5 glass 
 
 
 
Fig. 9 – Variation of ln A.C.(ω) versus 1000 / T at different 
frequencies for Se80.5Bi1.5Te16Ag2  glass 
 
 
 
Fig. 10 – Variation of ln A.C. with temperature 1000 / T in 
Se80.5Bi1.5Te18 – yAgy glasses at 1 kHz 
 
Table 1 – Values of activation energy ΔEA.C.(ω) at different frequencies for Se80.5Bi1.5Te18 – yAgy glasses 
 
Frequency 
ΔEA.C.(ω) 
Se80.5Bi1.5Te18 Se80.5Bi1.5Te17Ag1 Se80.5Bi1.5Te16.5Ag1.5 Se80.5Bi1.5Te16Ag2 
50 Hz 3.37234 3.29806 2.97486 1.36003 
100 Hz 2.94961 3.22515 2.95997 1.3584 
500 Hz 2.0437 2.85743 2.79491 1.33799 
1 KHz 1.61295 2.53763 2.64512 1.31188 
10 KHz 0.56483 1.17601 1.63319 1.07895 
50 KHz 0.2464 0.53787 0.79083 0.72308 
100 KHz 0.17217 0.36606 0.53681 0.53233 
500 KHz 0.08137 0.13485 0.19615 0.22927 
 
here ΔEA.C.(ω) is the A.C. activation energy and 0(ω) is 
the pre exponential factor. The values of activation 
energy ΔEA.C.(ω) at different frequencies are reported in 
the Table 1. 
It is found that a.c. activation energy ΔEA.C.(ω) de-
creases with an increase in frequency which is in accor-
dance with the earlier results [27, 36]. This decrease may 
be attributed to the increase in applied field frequency, 
which enhances the electronic jump between localized 
states. The obtained results of A.C. activation energy for 
the samples support the hopping conduction mechanism. 
 
 A.C. CONDUCTIVITY OF AG INCORPORATED SE-TE-BI GLASSY ALLOY … J. NANO- ELECTRON. PHYS. 5, 02020 (2013) 
 
 
02020-5 
4. CONCLUSIONS 
 
The effect of Ag incorporation on the A.C. conductivity 
has been  studied in Se80.5Bi1.5Te18 – yAgy (y  0, 1.0, 1.5 
and 2.0) alloys in the frequency range 1-500 kHz over the 
temperature range 300-355 K, using parallel impedance 
measurements. The temperature dependence of A.C. 
conductivity and the exponent s are discussed in terms of 
the correlated barrier hopping (CBH) model which indi-
cates that A.C. conductivity ( ) is proportional to s, 
s < 1 and decreases with increasing temperature.  
A.C. conductivity (ω) as a function of frequency, at 
different temperatures, is found to increases with an  
increase in frequency for all compositions. The frequency 
exponent s is found to decrease with an increase in tem-
perature which indicates that the correlated barrier 
hopping is the possible conduction mechanism in the 
investigated samples. The frequency dependence of A.C. 
conductivity and temperature dependence of s (frequen-
cy exponent) show that these glasses exhibit the hopping 
conduction type mechanism. Hence, correlated barrier 
hopping (CBH) model may be employed to describe the 
conduction mechanism in the investigated compositions. 
 
ACKNOWLEDGEMENT 
 
One of the authors is very grateful to 
Dr. Dhaneshwari Sharma for her valuable and kind co-
operation during this work.  
 
 
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A.C. Conductivity of Ag Incorporated Se-Te-Bi Glassy Alloy

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