S.C. COLAK, E. ARAL Physics Department,Faculty of Art and Science, Osmangazi University, Eskişehir, TURKEY.

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1 BALKAN PHYSICS LETTERS c Bogazici University Press 21 October 2009 BPL, 18, , pp. 1-7 (2009) ELECTRICAL CONDUCTIVITY OF BLACK-SODIUM-PHOSPHATE GLASSES S.C. COLAK, E. ARAL Physics Department,Faculty of Art and Science, Osmangazi University, Eskişehir, TURKEY. sccolak@ogu.edu.tr Abstract. - P 2O 5-Na 2O-CaO-Al 2O 3:CoO glasses containing two different amounts of V 2O 5 and CuO were prepared by the melt quench technique and their non-crystallinity has been established by XRD studies. The glasses were investigated for dc electrical conductivity in the temperature range K and activation energies were determined. Also, SEM micrographs and EDX spectra have been taken to investigate the morphological properties and elemental analysis, respectively. 1. Introduction Phosphate glasses are both scientifically and technologically important materials because they generally offer some unique physical properties better than other glasses, such as high thermal expansion coefficients, low melting and softening temperatures, high electrical conductivity, ultraviolet (UV) transmission and optical characteristics [1-6]. These glasses are known for lower glass transition temperatures and greater thermal expansion, and have attracted considerable interest in recent years because of their potential for technological applications, especially in optics [7], and particularly in laser systems and biomaterials research [8-10]. The phosphate glasses have a large value of electrical conductivity in comparison with other glass systems such as silicates and borates and, thus, are the prime candidates for superionic conductors and electrolytes [11]. Glasses with high concentrations of transition metals are interesting because of their semiconducting properties [12-16] and optical absorption in the visible, resulting in coloration of the glass [17] states. Glasses are being used as electrically conductors or insulators in many applications. Glass is being used in wide spread in different fields such as production of various lamps, valves, different sized insulators and electronic circuitry elements in electrical-

2 2 BALKAN PHYSICS LETTERS electronical industry [18]. Therefore, understanding of electrical conductivity of glass is important. In this study, black glass has been produced by doping CoO to P 2 O 5 - Na 2 O - CaO - Al 2 O 3 glass structure in high ratios, the effects of electrical conductivity of V 2 O 5 and CuO, which are the transition metal ions, on this black glass has been investigated. 2. Experimental Glass samples used in the present study were prepared by the melt quench technique and their starting batch compositions are listed in Table 1 in weight. Table 1: Compositions of the all glasses (in wt%) studied in the present work Glass Code Glass Structure P1 %60 P 2 O 5 + %20 Na 2 O + %18 CaO + %2 Al 2 O 3 (bulk glass) P2 bulk glass + %20 CoO (black glass) P3 black glass + %0.5 V 2 O 5 P4 black glass + %1 V 2 O 5 P5 black glass + %0.5 CuO P6 black glass + %1 CuO Reagent first been carefully were weighed, then mixed. The mixtures were placed in a platinum crucible and placed in an electric furnace for 1 hour at 1300 o C with certain intervals; molten glass samples were taken out and stirred to ensure homogeneity. After one hour, molten glass samples were taken out of the electrical furnace and poured into a graphite mould and 35mm high cylindrical glass blocks, having a diameter of 25mm were obtained. These cylindrical glass blocks were taken out of the mould in order to prevent breaking and cracking and kept in the sintering furnace at 350 o C for one houre, then cooled slowly to room temperature. These glass blocks were cut by a cutting device having a diamond disc into 2.5mm thick discs to facilitate measurement; by grinding and polishing, coins having parallel and shiny surfaces were obtained. The X-ray diffraction (XRD) studies of all samples of sodium phosphate glasses were recorded on a Rigaku Rint 2000 X-ray powder diffractometer using Cu Kα radiation. ( λ = Å ) in the range of 2θ between 10 o and 70 o. The morphologies of the surfaces and fracture surfaces of all samples were observed by scanning electron microscopy (SEM) on a Jeol JSM 5600 LV. Surfaces were covered with golden before microscopic observation. Energy Dispersive X-ray (EDX) analysis was accomplished on a NoranVoyager-EDS The direct current conductivity (DC) measurements were performed with a KEITH- LEY 6517A electrometer in the temperature range K. The conductivity of

3 3 glasses was determined by the well-known hot probe method. 3. Results and Discussion X-ray diffraction studies X-ray diffraction patterns confirmed the amorphous state of the investigated all glasses Figure 1. XRD pattern of P 1 glass. Figure 1 gives the XRD diffraction pattern of glass P 1. The XRD diffraction patterns of all of the glasses are similar. Although a peak is seen around 2θ = 30 o, it is understood that the crystallization was not realized since the peaks are wide and with low amplitude. XRD patterns of other glasses show the same behavior. So, all of the glasses have amorphous structure. SEM images has been taken to examine the surface characteristics and EDX spectra has been taken to elemental analyze of produced samples. When SEM images in Figure 2 is examined; it is seen that the glass surfaces are not homogenous and there are large and small structures that are not enter to the structure. On the other hand, it has been understood from EDX spectra that the amounts of cobalt are almost the same in all the doped glasses. For this reason, we think that the cobalt is homogenously distributed and it is not cobalt that disturbing the homogenity of these structures. When comparing the EDX spectra of all of the glasses, it is concluded that phosphorus or calcium is not dissolved completely in glass. It is thought that more homogenous structures can be obtained by increasing the working time and working

4 4 BALKAN PHYSICS LETTERS temperature. The atoms of phosphorus were formed a more homogenous surface by entering the structure when glass P 2 (b) were obtained by making CoO doping to glass P 1 (a). When V 2 O 5 doping was increased, the (c-d) surface homogenity was disturbed, however when CuO doping was increased, the (e-f) surface homogenity became better. Figure 2. SEM micrographs and EDX spectrums of all glass.

5 dc Conductivities Fig. 3 shows the relation between dc conductivity (σ) and [10 3 /T ] for all samples. The linear relationship between the logarithm of dc conductivity and inverse of temperature for all the samples indicates that the following Arrhenius law is satisfied: σ = σ 0 exp( E a /kt ) (1) where o is the pre-exponential factor, k is Boltzmann s constant and Ea is the activation energy for conduction. The calculated values of (at 373K) and Ea for all the glasses are included in Table 2. By increasing the temperature, the electrical conductivity increases in all samples. While electrical conductivity is increasing slowly with the temperature in low temperature region in all glasses, it increases fast in high temperature region in glasses P 3 and P 6. Table2.The calculated values of σ (at 373 K) and E a (at two different range) for all the glasses. Glass Code σ at373k (S/cm) E a (MeV) P P P P P P Figure 3. Variation of ln (σ) as a function of reciprocal of temperature for all glasses.

6 6 BALKAN PHYSICS LETTERS 4. Conclusions In order to investigate the structural characteristics of prepared glasses,xrd patterns has been used. The crystalline structure was not encountered in XRD patterns and it has been observed that they were in amorphous structure. When SEM images were examined, it has been observed that the surface is not homogenous. From EDX spektra, it has been observed that CoO in high ratios improves the surface structure and when V 2 O 5 doping increased, the surface homogenity was disturbing, and when CuO doping increased, the surface homogenity was increased. The change of electrical conductivity of produced glasses with respect to temperature has been observed in this study. The electrical conductivities of all of the samples are increasing with increasing temperature. When the conductivities at a constant temperature (at 373 K) were examined, it has been observed that the values were changing between S/cm. While the glass with the highest electrical conductivity is 1% CuO doped glass (P 6), the glass with the lowest conductivity is 0, 5% V 2 O 5 doped glass (P 3). The 20% CoO doping to the base glass which is transparent lowers the electrical conductivity. However the conductivity of this glass has higher values than the many of the glasses investigated in the literature, as well. Also while the concentration of V 2 O 5 and CuO doped on this black glass was increased, the values of electrical conductivity increased. For this reason, it can be said that electronic conductivity plays role in conduction mechanism. Activation energies have been calculated using the plot of electrical conductivity versus temperature. Activation energy decreases with the increase ofv 2 O 5 doping ratio while it increases with increasing CuO amount. REFERENCES [1] Wilder, J. A., J. Non-Cryst. Solids, 38-39, 879, [2] Ray, N. H., Lewis, C. J., Laycock, J. N. C., Robinson, W. D., Glass Technol., 14(2), 50, Ray, N. H., Lewis, C. J., Laycock, J. N. C., Robinson, W. D., Glass Technol., 14(2), 55, [3] Sidek, H. A. A., Collier, I. T., Hampton, R. N., Saunders, G. A., Bridge, B., Phil. Mag. B., 59, 221, [4] Kordes, E., Nieder, R., Glastech. Be., 41, 41, [5] Proulx, P. P., Cormier, G., Capobianco, J. A., Champagnon, B., Bettinelli, M., J. Phys. Condens. Matter, 6, 275, [6] Sharaf El-Deen,L.M.,Al Salhi,M.S.,Elkholy,M.M.,Journal of Non-Crystalline Solids,354, ,2008. [7] Weber, M. J., 1990, J. Non-Cryst. Solids, 123, 208. [8] Kumar, B. and Lin, S., 1991, J. Am. Ceram. Soc, 74, 226. [9] Ducheyne, Pv, 1998, MRS Bull.vv 23, 43.

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