Conductance and Loss Factor: A Study in (ZnO-PbCrO 4 ) Mixed Material

Transcription

1 Conductance and Loss Factor: A Study in (ZnO-PbCrO 4 ) Mixed Material Dr. Meenu Singh Sachan, Department of Applied Sciences & Humanities,Jasdev S. Sandhu Inst. Of Engg. & Tech. Kauli; Patiala, Punjab, India Abstract In this work the variation of conductance(g) and Loss factor (tanδ) of (ZnO- PbCrO 4 ) mixed material with composition, intensity of illumination, frequency a.c field and temperature have been studied. The mixed material of PbCrO 4 and ZnO were prepared by heat treatment technique taking firing temperature 600 C for 35 minutes. The best result obtained with (75% ZnO-25% PbCrO 4 ) composition.for measurement purpose the thick binder layer (cell) were fabricated in the form of parallel plates capacitor. Conductance (G) and Loss factor (tanδ) of binder layer have been measured in frequency range (1kHz 40kHz) with intensity of illumination 1200 lux and temperature range 31 C to 77 C.The loss factor decreases with increasing frequency this is due to less space charge formation in a dielectric.the conductance in dark (G D ) and in light (G I ) decreases upto 40 C and then start increasing beyond that temperature is due to the contribution of frequency independent d.c conduction. Keywords: Dielectric, Loss factor, Mixed material, Conductance, Thick binder layer Introduction The dielectric properties of insulators are also important to a wide range of electrical product, where rapid manufacturing parts may be used as components or housing. There are several different dielectric properties like Dielectric loss (tanδ), Dielectric constant, Volume Resistivity, surface Resistivity, Conductance etc. that can be used to quantity the Dielectric performance of material and depending upon the applications. The loss factor (tanδ) represents the energy loss from the absorption process, and is a ratio of the energy which is dissipated to the energy which is stored in the materials. When certain photoconducting material are placed as a dielectric in sandwiched type cell in presence of alternating field, the radiation absorbed by the photoconductor increases the capacitance(c), conductance(g) and dielectric loss (tanδ). This phenomenon is known as Photodielectric effect (PDE)[1].These studies have been made in several material like ZnS in ZnO [2], CdS powder and in single crystal[3][4]. The dielectric properties were studied on polymers [5] and solution and poly film [6]. The a.c conductance and dielectric properties were also carried on the sheet of polycarbonate [7]. Change in dielectric properties in presence of light is essentially another manifestation of photoconductivity was investigated by Kallmann[8],[9]. According to Garlic and Gibson [10] the change in capacitance (C), conductance (G) and loss factor (tanδ) is due to real change in the dielectric constant arising bound to certain trapping centre.the dielectric properties like capacitance, conductance and loss factor are controlled by the intensity o illumination, a.c. field frequency and temperature [11],[12]. The capacitance increase with increasing intensity of illumination.the space change is observed only in the lower frequency region. The variation of the a.c. conductance with frequency may be due to the variation in the formation of space change. Study of dielectric properties have been made on number of materials [13][14][15]. But mixed material have been relatively less reported demands for special material led to the conception of composites, since valuable properties of different types of material can be combined. So, In this paper study is made on (ZnO-PbCrO 4 ) mixed material in thick binder layer. Experimental Detail The mixed material of ZnO and PbCrO 4 was synthesized by heat treatment technique. For this high purity PbCrO 4 and ZnO were taken in different proportions by weight and ground properly in order to get homogeneous mixing. This mixture was then fired in a ceramic tube in a cylindrical furnace in air atmosphere. Then heated material was suddenly quenched to room temperature and again ground. For measurement purpose the cells were fabricated in the form of parallel plate capacitors, by embedding the sensitive material in polystyrene binder and sandwiching it between Aluminium plate and conducting glass plate. The cell area was 2.25 cm 2 and the thickness was varied from cm to cm. For the change of field frequency and voltage arbitrarily, two conducting glass plates were connected at the ends of the capacitor. This makes the cell a four electrodes system. The capacitance and conductance were measured through an a.c. bridge LCR-Q meter. The external field was obtained through an oscillator cum amplifier assembly. The cell was mounted in a chamber under complete darkness and radiations from Hg-lamp (300 W) were allowed through a window over the transparent surface of the cell. Open Access Journals Blue Ocean Research Journals 4

2 Results And Discussions Five mixed materials of ZnO and PbCrO 4 having different compositions i.e (100%ZnO), (75%ZnO-25% PbCrO 4 ), (50%ZnO-50% PbCrO 4 ), (25%ZnO-75% PbCrO 4 ) and (100% PbCrO 4 ) were prepared by heat treatment. Various synthesizing parameters such as firing temperature, time and composition (% of PbCrO 4 )of the sample were changed to get optimum conditions of dielectric properties change (PDE). The best result was observed in (75%ZnO-25% PbCrO 4 ) sample heated at 600 C for 35 minutes. So the measurements have been made for this composition. The variation of conductance (G) and Loss factor (tanδ) with intensity of illumination, a.c field frequency and temperature were measured.the results are as following: Effect Of Intensity Of Illumination The variation of conductance (G) and Loss factor (tan δ) with intensity of illumination are shown in Table 1(a), 1(b) and Table 2(a), 2(b) respectively. The measurements have been made for two different samples i.e. (75%ZnO - 25% PbCrO 4 ) and (25%ZnO-75% PbCrO 4 ) compositions. Study of capacitance for this mixed material (ZnO- PbCrO 4 ) was also measured and presented in paper [16]. TABLE 1(a): Variation of Conductance (G) with for (75% ZnO- 25% PbCrO 4 ), (Frequency = 1 khz, a.c field = volt/cm, N0. Conductance (G) ( in Ω -1 ) Table 1(b): Variation of Conductance (G) with Intensity of Illumination for (25% ZnO- 75% PbCrO 4 ), N Conductance (G) ( in Ω -1 ) For both the capacitance initially increases with intensity of illumination then saturation is observed in higher light intensity side. This is due increase in space charge. Space change is an electric inhomogenenity appearing in the material [17] which causes dielectric losses.the probable mechanism for space charge formation are a) Polarization of equilibrium charge carries under the action of electric field. b) Polarization of photo generated carries. c) Injection of charges carriers from the electrode. Space charge is formed (a) near the electrode (b) around the boundaries and (c) both within the volume and at the surface of the bulk. More and more charge carriers are generated with increasing intensity of illumination. This increases the total space charge due to photogenerated carriers. The measured ac conductivity would always consists of the sum of the frequency independent d.c conductivity.the d.c. conductivity increases with intensity hence total conductance increases with intensity of illumination (both G D and G I ). Table 2(a): Variation of loss factor (tan δ) with Intensity of Illumination for (75% ZnO- 25% PbCrO 4 ), x x x x x x x10 2 Loss Factor (tan δ) Table 2(b): Variation of loss factor (tan δ) with Intensity of Illumination for (25% ZnO- 75% PbCrO 4 ), x x x x x x x10 4 Loss Factor (tan δ) The loss factor (tanδ ) increases slowly with light intensity. The tan δ calculated using the formula tanδ=g/ωc here G is conductance (G=1/R, R is resistance), ω is an- Open Access Journals Blue Ocean Research Journals 5

3 gular frequency (2πf) and C is capacitance. As the intensity of illumination increases the number of charge carriers forming the space charge also increases, so tanδ increases. Effect Of Field Frequency Under fixed illumination of 1200 lux and volts/cm a.c field of variable frequency the variation of conductance is shown in Table.3(a).The a.c conductance decreases with frequency upto 5 khz but increases beyond 5kHz both in dark and light. The variation of a.c. conductance with frequency may be due to the variation in the formation of space charge.the space charge formed around the boundaries restricts the transport of charge carriers from one grain to another, thereby reducing the conductivity with increasing frequency. Higher value of G D and G I in higher frequency region is due to dipolar relaxation effect. Table 3(a): Variation of Conductance (G) with frequency for (75% ZnO- 25% PbCrO 4 ), (Intensity of illumination =1200 lux, a.c field = volt/cm, Frequency (in khz) Dark G D (in Ω -1 ) Light G I (in Ω -1 ) The variation of loss factor (tanδ) with a.c frequency is shown in Table 3(b) for (75%ZnO-25% PbCrO 4 ) composition. Measurements have been made both in light and dark. The tanδ decreases with increasing frequency. The behaviour can be explained on the basis of the space charge is formation in a dielectric.as frequency is increased less and space charge formed thereby decreasing the dielectric losses. Table 3(b): Variation of loss factor (tan δ) with frequency for (75% ZnO- 25% PbCrO 4 ), (Intensity of illumination =1200 lux, a.c field = volt/cm,. Frequency (in khz) Dark (tan δ D ) Light (tan δ I ) Effect Of Temperature Table 4(a) and 4(b) shows the variation of conductance and loss factor with temperature respectively. The observations have been taken in dark as well as under illumination. Table 4(a) shows that G D and G I decrease upto 40 C and then start increasing beyond that temperature. This behaviour of G D is due to the contribution of the frequency independent d.c conductivity. The variation of loss factor with temperature is also shown in Table 4(b).The tanδ D and tanδ I both initially decrease with increasing temperature upto36 C, then increases in higher temperatures region. This may be attributed to the contribution of the frequency independent d.c conductivity towards the measured loss factor. For (75%ZnO-25% PbCrO 4 ) composition the conductivity initially decreases with temperature and then increases in higher temperature side. Slightly larger value of tanδ I is due to the photogenerated carriers which increases the space charge. Table 4(a): Variation of Conductance (G) with Temperature for (75% ZnO- 25% PbCrO 4 ), (Frequency = 1 khz, Intensity of illumination =1200 lux, a.c field = volt/cm) Temperature (in C) Conductance in Dark G D (in Ω -1 ) Light G I (in Ω -1 ) Open Access Journals Blue Ocean Research Journals 6

4 Table 4(b): Variation of loss factor (tan δ) with Temperature for (75% ZnO- 25% PbCrO 4 ), (Intensity of illumination =1200 lux, Frequency = 1 khz, a.c field = volt/cm.) Temperature (in C) Dark (tan δ D ) Light (tan δ I ) x x x x x x x x x x x x x x x x x x x x10 3 Conclusion This work shows that the variation of loss factor (tanδ) with intensity is less for (75%ZnO-25% PbCrO 4 ) composition. As d.c conductance increases with intensity, hence total conductance increases with intensity of illumination. The conductance decreases with increasing frequency is due to space charge formation around the boundaries of grains. Higher values of G D and G I at higher frequency region are due to doppler retardation effect. The variation of loss factor with intensity & frequency can be explained on the basis of space charge formation in a dielectric. Decrease in conductance and loss factor in lower temperature region (upto 40 C) is due to frequency independent d.c conductance and increase in these attributed to creation and destruction of dipoles leading to appreciable space charge polarization. The loss factor is an essential property of dielectric materials hence its determination is very important. Acknowledgment The author is thankful to Dr. H. S. Sahota, Dean Research & Development; JSSIET Kauli Patiala, Punjab for his valuable suggestions. References [1] Kallmann, Kramer and Parlmutter. Induced Conductivity in Luminescent Powder II AC Impedance measurements Phys. Rev. vol 89, no.4, pp , [2] R. K. Srivastava, S. G. Prakash, Photoelectret Study of Sm doped ZnO and ZnO-Pb 3 O 4 mixed lattice, Indian Journal of pure & Applied physics, vol.46,pp , [3] S. Suresh, Dielectric and Photoconductivity properties of L-Arginine Dilodate nlinear Optical Single crystal Materials Phys and Mechanics,vol15,pp.74-77, [4] J. Raux, L Effect Photodielectrique, J. Phys, Radium, vol 15,no.3, pp ,1954. [5] P. K. C Pillai and Rashmi, Dielectric properties of Polystyrene and some related Polymers.on line , [6] R.Singh, R.D.P Sinha, Amarjeet kaur and Jitendra kumar, A.C conductivity and Dielectric Relaxation Behaviour of solution Grown poly(vinylidence Fluoride) Films. Journal Ferroelectrics, vol 329, Issue1,(2005),pp [7] M.S. AZIZ and H.M El-Mallah, A.C. conductivity and Dielectric properties of polycarbonate sheet, International Journal of Polymeric Material ;vol. 54, issue. 12, pp ,2005. [8] Kallmunn, Kramer and Mark, Impedance measurements of CdS crystals Phys. Review, vol 99, pp , [9] Rajesh Kalia, Sunil Kumar, H.S. Bhatti, J.k. Sharma, Study of Dielectric Behaviour of nanoporous Polycarbonade membrane for future nano electret application, Digest Journal of Nanomaterial and Biostructures,vol.3, no.4, pp ,2008. [10] G.F.J. Garlick and A.F. Gibson, Dieclectric Charge In Phosphors Containing More Than One Activator Proc. Phys.Soc, vol 62, pp , [11] P.J. Harroop, Dielectric, John willey, New York, [12] P.K.C. Pillai, R. Nath & R.C. Ahuja, PhotoDielectric effect In HGI2 =CDS system, Indian J. Pure and Applied phys. vol.14, no. 10, pp ,1976. [13] Nitin Pandey, R.K. Srivastava, Study Of Photoelectret Effect In Dysprosium Doped ZnO, Indian.J. Pure & Applied phys. vol.50 pp , [14] Sadhana Devi & S.G. Prakash, Ind. J. Pure & Applied Phys. vol 28, pp ,1990. [15] S. Ruhela, S.K. Srivastava, Study of Photo Dielectric Effect in Mixed Lattice of (Al 2 O 3 -ZnS) Cu, Open Access Journals Blue Ocean Research Journals 7

5 Cl International Journal of Scientific and Research Publications, vol.2, Issue 12,pp.1-4, [16] Meenu S. Sachan, Study of variation of capacitance in (ZnO PbCrO 4 ) Thick binder layer, International Journal of scientific & Research.vol3, Issue 6 (2014),pp [17] B.Tareev, Physics of Dielectric Materials, Mir Publishers; Moscow, p [18] A. Man Singh, Bull Mater. Sci. (Netherlands), vol.2, pp.325, Open Access Journals Blue Ocean Research Journals 8