Effect of annealing temperature on dc electrical conductivity properties of SnO 2 doped lead vanadate glass system

Transcription

1 International Research Journal of Materials Science and Engineering Vol. 4(1), pp , April, ISSN: IRJMSE Research Article Effect of annealing temperature on dc electrical conductivity properties of SnO 2 doped lead vanadate glass system * 1 Ponnada Tejeswararao, 2 Balireddy Vasundhara 1,2 Department of physics, GITAM Institute of technology, GITAM University, Visakhapatnam, Andhrapradesh, India Thermal and DC electrical properties investigations of xsno 2 (50-x) PbO: 50V 2O 5(X=5, 10, 15 in molar ratio) glasses were carried out using X-ray diffractrometer (XRD), Differential scanning calorimetry (DSC) and two probe techniques. XRD results shown that the Perfect vitrification has been achieved and DSC results have indicated that the substituent SnO 2 is replacing PbO in the glass network in such a way that the eutectic composition is maintained. The DC electrical conductivity studies on SnO 2 substituted glass systems annealed at C as well as C and C indicated that the conductivities increased as the annealing temperature is increased. activation energies also changed as the annealing temperature is changed. Keywords: XRD, DSC, DC Conductivity, annealing temperature, semiconducting glasses INTRODUCTION In the conventional silicate-based glasses electrical conduction takes place due to ionic transport. In semiconducting glasses the electrical conduction is due to the transport of electrons from low valancy state to high valancy state (Mott N.F, 1968; Austin I.G et al,1969; Sayer M et al,1972; Chung C.H et al, 1980; Ghosh A et al,1986). The research in understanding the structural and physical properties of glasses in general and semi-conducting glasses in particular has increased considerably due to the potential applications perceived for semi-conducting glasses. Some of the possible applications are in threshold switching, memory switching, electrochemical batteries etc. Studies are carried out on semi-conducting glasses in bulk as well as thick film form. Among all PbO- V2O5 glasses have been of great interest due to their ease of preparation (Ghosh A,1988; LivageJ et al, 1990; Sakuri Y et al 1985; Peng B et al, 2005) as compared to other semiconducting glasses. In the present work, we prepared the glass samples by adding SnO2 in different molar ratios into a chosen glass matrix ((50-x) PbO: 50 V2O5) and discussed the study of compositional and temperature dependence of D.C. electrical properties of SnO2 substituted lead vanadate glasses in the temperature range 300K to 500K. Experimental A series of glass with the molar formula x SnO2 (50-x) PbO: 50 V2O5 (X=5, 10, 15 in molar ratio) were prepared. Appropriate amounts of reagent grade SnO2, PbO and V2O5 were well mixed and melted in silica crucibles using an electrical furnace at a temperature ranging between C C range, depending on the glass composition. The melt was swirled frequently to insure the homogeneity the melts were quenched on a large stainless-steel block maintained at room temperature ( 30 0 C) and constituting of 9mm cylindrical cavities to get samples of cylindrical shape of 2 to 3mm width. The glass samples were annealed at C below the glass transition temperature for nearly 2 hours. The samples were washed with an acetone and dried. The glasses were stored in desiccators until required In the present studies, XRD recordings of the powdered glass samples were recorded with the help of a PAN Alytic X Pert-PRO diffractrometer using Cu Kα radiation at Ǻ and diffractrometer settings in the 2θ range from 10 0 C-70 0 C by changing the 2θ with a step size of The density (D) was determined at room temperature using Archimedes principle. The samples were weighed *Corresponding author: Ponnada Tejeswararao, Department of physics, GITAM Institute of technology, GITAM University, Visakhapatnam, Andhrapradesh, India. blue.teja@gmail.com

2 Tejeswararao and Vasundhara 036 Using an electrical balance (Dhona Model 200D) of gm accuracy. The weight loss was measured in an acetone (Aldrich) of 99.5% Purity and density gm/cm 3. In the present studies, DuPont, USA make model 2000 thermal analyzer was used to determine the glass transformation temperature (Tg), crystallization temperature (Tc) and melting temperature (Tm). DSC scans were conducted using 5-10 mg ground as-cast glass specimens which are heated with heating rate of 10 0 C/min between 0 and C in a platinum crucible. Alumina powder was used as the reference material. The DC electrical conductivity studies were carried out by using a two-probe technique. A homemade muffle furnace using a super kanthal wire as a heating element was used for temperature variation studies in the range 300K 500K. Temperatures of the furnace as well as the sample are monitored by using a Cr Al thermocouples. The resistance of the samples was measured using a Keithaly (Model 614) digital electrometer. The conductivity was calculated from a knowledge of the geometry of the sample using the expression. σ = (t/rx ) A (1) Where RX is the resistance, t is the thickness and A is the area of the sample. RESULTS AND DISCUSSION The X-ray diffractograms annealed at 150 c and c containing (x=5, 10, 15 mole %) of SnO2 showed no trace of crystallinity and are shown in Figure 1 and Figure 2. The X ray diffractogram of sample annealed at C is showing crystalline peaks (Figure 3). Figure 1. X- ray diffractograms of xsno 2 (50-x) PbO:50V 2O 5 Figure 2. X- ray diffractograms of 15SnO 2 35PbO: glass system annealed at C 50V 2O 5 glass system annealed at C. (a) x= 5 mole% (b) x=10 mole% (c) x=15 mole% Figure 3. X- ray diffractograms of 15SnO 2 35PbO: 50V 2O 5 glass system annealed at C.

3 log 10 (ohm -1 cm -1 ) Int. Res. J. Mat. Sci. Engin. 037 The DSC patterns for these glass systems shown in Figure 4 are slightly different when compared to the unsubstituted system (Ramesh K.V, 2000). Values of glass transition temperature Tg, crystallization temperature Tc, melting temperature Tm, glass forming tendency Kg and densities of the xsno2 (50-x) PbO: 50V2O5 are given in Table1 and these results suggest that SnO2 acts as a network modifier where as PbO acts as a network former. As seen in Figure 4 up to x= 15 mole% there is only one endothermic peak corresponding to melting point. This indicates that the substituted samples behave like the eutectic composition up to x=15 mole%. samples annealed at C. At a given temperature the conductivity increases as SnO2 substitution increases. The SnO2 substituted glasses exhibit higher activation energy when compared to those of 50 PbO: 50V2O5 system. Figure 5. Temperature dependence of logarithmic conductivity of xsno 2 (50- x) PbO:50V 2O 5 glass system annealed at C x= 5% SnO x=10% SnO x=15% SnO 2 x= 0% SnO Figure 4. Differential scanning calorimetry curves of xsno2 (50-x) PbO: 50V2O5 glass system. (a) x= 5 mole% (b) x= 10 mole% (c) x=15mole% In order to understand the devitrification tendency and thermal stability of the glass samples, glass forming tendency values Kg are calculated using the following equation. Kg = (Tx - Tg) / (Tm Tx) (2) Where Tx is the beginning of the first exothermic reaction where the crystallization starts. Lower value of Kg indicate that the tendency of crystallisation is more and thermal stability is less. (Tejeswararao P et al, 2016). Kg represents the temperature interval during nucleation. the experimental values indicate that the 5SnO2 45PbO:50V2O5 glass samples have lowest thermal stability among four compositions, with a Kg value of The densities seem to be increasing with an increase in SnO2 substitution (Tejeswara Rao P et al 2012) The logarithmic DC conductivity (log10) as a function of reciprocal of temperature for the three different values of x (the molar fraction of dopant) is given in Figure 5 for /T(K -1 ) Figure 6. Temperature dependence of logarithmic Conductivity of xsno 2 (50- x) PbO: 50V 2O 5 glass system annealed at C. When the samples were annealed at C for two hours, (Figure 6) the conductivity behaviour seems to be similar to that of the samples annealed at C except that all the samples exhibit higher conductivity (Figure 5). The conductivity still increases as concentration of SnO2 substitution increases. The activation energy remains almost the same for all SnO2substituted samples. T. The conductivities were also measured for the samples devitrified after annealing at C for five hours (Figure 7). There is a drastic increase in conductivities of all the samples. The conductivities of the substituted samples still seem to increase with an increase in the amount of SnO2 substitution.

4 log 10 (ohm -1 cm -1 ) Tejeswararao and Vasundhara x=5% SnO 2 x=10% SnO 2 x=15% SnO 2 x=0% SnO /T(K -1 ) Fig. 7. Temperature dependence of logarithmic conductivity of xsno 2 (50-x) PbO:50V 2O 5 glass system annealed at C Table 1. Values of glass transition temperature (Tg), crystallization temperature (TC), melting temperature(tm) and glass forming tendency (K g ) for the xsno2 (1-x) PbO:50V2O5. Glass Composition (mole %) Temperature( 0 C) V2O5 PbO SnO2 Tg ( 0 C) Tc ( 0 C) Tm ( 0 C) Kg , , , , But the conductivities of all the devitrified samples seem to be less than that of the devitrified 50 PbO: 50V2O5 system at higher temperatures. However, activation energies of SnO2 substituted devitrified samples seem to be less than that of the 50 PbO: 50V2O5 devitrified sample. The activation energies obtained in the present studies are given in Table 2. The dependence of conductivity and activation energy on the annealing temperature in the present studies indicates a strong micro structural dependence. Table 2: energies obtained at different temperature regions by fitting Mott s model for SnO 2 substituted lead Vanadate glasses. Glass composition energies of energies of energies of (mole %) the samples the samples the samples annealed at annealed at annealed at V2O5 PbO SnO C C C The microstructure of the glass network may be varying such that new conducting path ways are established. In literature there are examples for such micro structural dependence of conductivity. Chung and Mackemzie studied electrical properties of 55V2O5:45GeO2 and 55 V2O5:45TeO2 glass systems (Murawski L et al,1979). They should showed that the conductivities and activation energies of the samples changed depending on the temperature of melting which changed the V 4+ ion concentration relative to total vanadium ion concentration. They also observed that the conductivities and activation energies changed as the annealing temperature increased. However, it must be mentioned here that SnO2 doped lead meta vanadate glasses in the present studies exhibit much higher conductivities and lower activation energies when compared to 55V2O5:45GeO2 or 55V2O5:45TeO2 samples reported by Chung and Mackezie (Murawski L et al,1979) and also observed that the conductivities are increasing as the annealing temperature is changing in the increasing order (150 0 C C C). We consider the above temperatures for annealing the samples to understand how the conduct ivies are changing at near the glass transition temperature (225 0 C) and crystallisation temperature (380 0 C). Kinser and Wilson (Kinser D.L et al,1972) studied the electrical properties and the corresponding microstructures of vanadium phosphate glasses and suggested that the observed conductivity maximum at C (Concentration of V4+/V Total)< 0.5 is a consequence of micro structural segregation. Similarly, according Anderson and Mac Crone in iron silicate glasses the majority of iron ions are supposed to be situated in relatively well-ordered clusters which might be giving rise to high electrical conductivity in these glasses (Anderson R.A et al, 1974). In literature there are instances of V2O5 containing glasses showing maximum conductivity at different values of C (Concentration of V 4+ /VTotal) (Austin I.G et al, 1969). These differences are attributed to Polaron- Polaron interactions and short range coulomb repulsion which modifies C in Mott s equation (Sayer M et al,1972) to C (1-C) n. These examples suggest that diffusion like conduction mechanism in the glass systems containing random distribution of ion sites may be inappropriate. These discrepancies are supposed to be explained by a model proposed by Anderson and Mac Crone (Anderson R.A et al, 1974). In which the charge carriers are supposed to move along paths along high conductive chains of transition metal ions. Therefore, it is possible in the present glass systems such conductive chains of transition metal ions might be existing and these conductive chains may be micro structural dependent and vary as microstructure varies as a function of temperature. CONCLUSIONS Perfect vitrification has been achieved for all the glass samples as can be seen from their X-ray diffractograms of

5 Int. Res. J. Mat. Sci. Engin. 039 the as prepared samples after annealing at 150 o C and 225 o C for two hours. DSC recordings show that eutectic composition of the lead meta Vanadate has been maintained for all the glass systems up to 15 mole% of substitution. The DSC data also indicates that all the glass systems are characterized by more than one crystallization peak. This can be thought that of as an evidence for the existence of more than one meta stable phase in the glass systems. The dopant SnO2 is not divalent oxides like PbO. Besides SnO2 is known to be glass formers unlike PbO which is considered to be a glass modifier. In spite of these differences, the present observations indicate that these substituents are replacing PbO in the glass network in such way that the eutectic composition is maintained and the final devitrified system has a crystal structure that is similar to that of lead meta vanadate. The DC electrical conductivity studies on SnO2 substituted glass systems annealed at C as well as C indicated that the conductivities increased as the annealing temperature increased. The activation energies also changed as the annealing temperature is changed. These differences are attributed to not only a change in the value of C (concentration of V 4+ /total vanadium concentration) but also a change in the microstructure of the glass system. However, all devitrified glass samples annealed at C show increased conductivity which is attributed to increase in the order of the crystalline system which reduces scattering of the electrons in their conduction paths. REFERENCES Anderson R.A, Mac Crone R.K(1974), Journal of Non crystalline solids. 14: Austin I.G., Mott N.F(1969). Polarons in crystalline and non-crystalline materials, Adv.Phys.18:41. Chung C.H, Makenzie J.D (1980),J. Non-Cryst.Solids. 42:151. Ghosh A (1988)., Memory Switching in Bismuth-Vanadate Glasses, J. Appl. Phys. 64: Ghosh A, Chaudhuri B.K. (1986), J. Non-Cryst.Solids. 83:151. Kinser D.L, Wilson L.K,, Sanders H.R, Hill. DJ (1972), Journal of Non crystalline solids, 8-10: 823, 830. LivageJ, Jolivet JP,Tron E(1990), Electronic Properties of Mixed Valence Oxide Gels, J. Non-Cryst. Solids.121: Mott N.F (1968). Dissertation, Solids, J. Non- Cryst.Solids.1:1-17. Murawski L, Chung C.H, Mackenzie J.D (1979), Electrical properties of oxide glasses process is carried out under controlled atmospheres. Journal of Non-Crystalline Solids. 32: Peng B, Fan ZC, Qiu XM, Jiang L, Tang GH, Ford HD, et al (2005), A novel transparent vanadate glass for use in fiber optics. Adv Mater, 17: Ramesh, K.V. (2000), Thermal, Electrical and Spectroscopic Studies of CuO, ZnO and TiO2 Substituted for PbO in Eutectic Lead Vanadate Glass System. Ph.D. Thesis, Andhra University, Visakhapatnam. Sakuri Y, Yamaki J (1985), V2O5 P2O5 Glasses as Cathode for Lithium Secondary Battery, J. Electrochem. Soc.132: Sayer M, Mansingh A (1972). Transport Properties of Semiconducting Phosphate Glasses Phy.rev.B6:4629. Tejeswara Rao P, Ramesh K.V, Sastry D.L, (2012), Electrical and Spectroscopic Studies of the CdO Substituted Lead Vanadate Glass System vs Crystalline Form, New Journal of Glass and Ceramics. 2, Tejeswararao P, Ramesh K.V, Sastry D.L, (2016), ESR and DC Electrical Properties of Bi2O3-PbO-V2O5 Glass System. Physics and Chemistry of Glasses- European Journal of Glass Science and Technology Part B. 57: Accepted 16 December 2017 Citation: Tejeswararao P., Vasundhara B. (2018). Effect of annealing temperature on dc electrical conductivity properties of SnO2 doped lead vanadate glass system. International Research Journal of Materials Science and Engineering, 4(1): Copyright: 2018 Tejeswararao and Vasundhara. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.