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Synthesis, characterization and dielectric properties of K1 xnaxnbo3

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https://www.eduzhai.net International Journal of Materials and Chemistry 2012, 2(2): 47-50 DOI: 10.5923/j.ijmc.20120202.01 Synthesis, Characterization and Dielectric Properties of K1-xNaxNbO3 S C Bhatt*, Manish Uniyal Department of Physics, H.N.B Garhwal University, Srinagar (Garhwal), 246174, Uttarakhand, India Abstract The samples of K1-xNaxNbO3 (X=0.4, 0.2, 0) ceramics (PSN) have been prepared by the conventional solid- state reaction method and sintering process. The prepared samples have been characterized by XRD. All the prepared samples show orthorhombic structure at room temperature. Dielectric and Electrical properties of PSN system have been investigated in the temperature range 450C-2450C, and at 1MHz frequency. It is observed that dielectric constant, loss tangent and electrical conductivity increases with increasing temperature. Near the transition temperature dielectric constant, loss tangent and electrical conductivity of these samples show anomalous behaviour with temperature. Keywords Transition Temperature, Dielectric Constant, Loss Tangent, Electrical Conductivity 1. Introduction ABO3 Perovskite type materials are of considerable technological importance, particularly with respect to their physical properties such as ferro, pyro-and piezo-electricity, dielectric susceptibility, linear & non linear electro-optic properties etc. The change in physical properties is particularly large when the external conditions, such as temperature, pressure, electric-field, composition etc. are altered. Such effects occur in connection with the simultaneous presence of phase transition in the system, where the atomic structure of the perovskite changes either discontinuously or continuously into another form. The dielectric properties of ABO3 perovskite structure K1-xNax NbO3 for some of the compositions has been extensively studied at high temperature[1] and it shows a number of ferroelectric phases with high spontaneous polarization. The solid solution of ferroelectric KNbO3 and antiferroelectric NaNbO3 exhibits good piezoelectric properties[2,3]. Potassium Sodium Niobate ceramic (K1-xNaxNbO3) with perovskite structures are widely used for transducer applications with broad ranges of technologically important dielectric, piezoelectric, ferroelectric and electro-optic properties. The structure of PSN system at room temperature is basically of the orthorhombic type. K1xNaxNbO3 (x=0) is a particularly promising ferroelectric with its combination of relatively low dielectric constant ( ε1 = 155, ε 2 = 44, andε 3 = 980) with extremely high electro-optic coefficients (r42=380pm/V, r33=64pm/V). This * Corresponding author: scbhattin@yahoo.com,(S.C.Bhatt) Published online at https://www.eduzhai.net Copyright © 2012 Scientific & Academic Publishing. All Rights Reserved makes KNbO3 vary attractive for opto-electronic devices, including high-speed electro-optic switches, modulators, and frequency doublers[4-7]. Dielectric measurements on this material were first reported by Matthias and Remeika [8] and then by Shirane et. al.[9] and observed well defined ferroelectric hystersis loops from room temperature to 4000C, for compositions form about 10 to 100% (mol) of K in K1-xNaxNbO3. Dielectric properties were reported by Narayan Murty et. al. [10]. Cross [11] has predicted, theoretically, the phase-diagram of KNbO3-NaNbO3 mixture from phenomenological arguments. The mixing of NaNbO3 in KNbO3 ceramics play an important role on the ferroelectric Curie temperature, dielectric constant, grain size as well as the planer mechanical coupling coefficient (kp) value [12-13], because NaNbO3 is anti-ferroelectric at room temperature, when mixed with small amount of KNbO3, becomes ferroelectric, which creates interest in the present investigation to investigate this system with a varying composition and temperature range. In this paper, we report the results of investigation on dielectric constant, tangent loss and electrical conductivity of the ceramic system K1-xNaxNbO3 ( x=0.4, 0.2 & 0) prepared by solid state reaction method and sintering process, in the temperature range 450C-2450C, and at 1 M Hz frequency. 2. Preparation The starting material was dried at 2000C for one hour to remove absorbed moisture. Different compositions of K1xNaxNbO3 for (x=0.4, 0.2 & 0) were prepared by weighing the sodium carbonate, potassium carbonate and niobium penta-oxide (starting materials) in proper stoichiometric proportions. The mixture was calcined in the platinum crucible, in air, at 9500C for 2h, for carbonate removal. 48 S C Bhatt et al.: Synthesis, Characterization and Dielectric Properties of K1-xNaxNbO3 After cooling, in dry air, the calcined mixtures were weighed to ensure complete carbonate removal. The pre-sintered mixture was ground and pressed into pellets of 10mm diameter. All the pellets were placed on a platinum crucible and sintered, in air, at 10500C for 26 h. The sintered pellets were electroded using air-drying silver paste for dielectric measurements. material sodium niobate in the mixed system of K1XNaXNbO3, which is in agreement with previous observations[1,18]. Lattice parameters of K1-XNaXNbO3 for different compositions at room temperature have been shown in table-A, which shows a decrease in lattice parameters as we add antiferroelectric material NaNbO3 in mixed system of K1-xNaxNbO3 ceramic. 3. Characterization X-ray powder studies were performed at room temperature with a SEIFERT 3000P X-ray diffractometer using filtered Cu K α 1 radiation of 1.5405980 A wavelength, in which, Ni, is used as filter. The instrument is well calibrated with silicon standard samples and the lines obtained are matching with the standard lines. At room temperature all PSN ceramic samples exhibit the orthorhombic symmetry. The sub cell parameters were obtained using the auto-X computer software and were compatible with those obtained earlier for ceramics [10,1217]. The results are summarized in following table- Table A. Lattice parameters of K1-XNaXNbO3 for different compositions at room temperature composition KNbO3 K0.8Na0.2NbO3 K0.6Na0.4NbO3 a 4.027 4.002 3.998 Lattice parameters oA b 4.057 4.040 4.011 c 3.958 3.946 3.919 4. Measurements The variation of dielectric constant, loss tangent and electrical conductivity at 1MHz frequency, in the temperature range 450C-2450C have been studied and plotted in Fig. 1, 2 & 3 respectively. These measurements were performed on HP Impedance Analyzer and FLUKE RCL meter, PM 6306. 5. Result and Discussions We have measured dielectric constant, loss tangent of K0.6Na0.4NbO3, K0.8Na0.2NbO3 and KNbO3 ceramic pellets using HP Impedance Analyzer and Fluke RCL meter PM 6304, at the temperatures from 450C to 2450C.The temperature dependence of dielectric constant, loss tangent and conductivity at 1MHz have been shown in Figs 1, 2 & 3, and tables-1,2 & 3, respectively. From these figures (Fig.1-3) and tables (Tables 1-3), it is observed that the mixed system of K1-xNaxNbO3 has a transition from orthorhombic to tetragonal at about 2200C. It is 2250C for KNbO3, 2150C for K0.8Na0.2NbO3 and 2050C for K0.6Na0.4NbO3, which shows that transition temperature from orthorhombic to tetragonal shifts towards lower temperature as we increases the quantity of anti- ferroelctric Dielectric constant 45 65 85 105 125 145 165 185 205 225 245 160 140 120 100 80 60 40 20 0 KNbO3 K0.8Na0.2NbO3 K0.6Na0.4NbO3 Te m pe rature (0C) Figture 1. Variation of dielectric constant with temperature for K1xNaxNbO3 at 1 MHz Table 1. Variation of dielectric constant with temperature for K1-xNaxNbO3, at 1 MHz frequency Temperature 0C 45 55 65 75 85 95 105 115 125 135 145 155 165 175 185 195 205 215 225 235 245 KNbO3 76.17 76.17 76.52 76.88 77.22 77.39 77.71 78.58 79.18 81.10 82.74 83.95 85.14 86.13 87.35 88.54 89.39 89.73 98.58 97.17 96.60 K0.8Na0.2NbO3 70.57 069.88 071.41 076.81 083.57 087.35 092.11 096.23 097.81 102.61 105.50 107.75 110.37 115.11 120.25 135.34 149.11 144.07 141.05 139.48 140.48 K0.6Na0.4NbO3 83.680 81.910 83.270 88.670 95.320 99.690 105.20 110.40 112.06 115.49 120.27 124.01 127.45 130.77 134.93 148.03 141.86 139.39 138.67 143.46 147.98 Tangent loss 0.25 0.2 0.15 0.1 0.05 0 45 KNbO3 K0.8Na0.2NbO3 K0.6Na0.4NbO3 95 145 195 245 Temperature (0C) Figture 2. Variation of tangent loss with temperature for K1-xNaxNbO3 system at 1 MHz International Journal of Materials and Chemistry 2012, 2(2): 47-50 49 Table 2. Variation of loss tangentfor K1-xNaxNbO3, with temperature, at 1 MHz frequency Temperature 0C 45 55 65 75 85 95 105 115 125 135 145 155 165 175 185 195 205 215 225 235 245 KNbO3 0.033 0.034 0.035 0.035 0.035 0.035 0.036 0.038 0.043 0.046 0.040 0.032 0.032 0.038 0.037 0.037 0.038 0.038 0.040 0.044 0.045 K0.8Na0.2NbO3 0.064 0.051 0.049 0.060 0.068 0.060 0.054 0.049 0.047 0.048 0.050 0.050 0.050 0.050 0.055 0.066 0.082 0.102 0.110 0.114 0.117 K0.6Na0.4NbO3 0.082 0.066 0.065 0.074 0.080 0.073 0.065 0.057 0.054 0.055 0.055 0.055 0.053 0.051 0.056 0.067 0.086 0.130 0.148 0.171 0.195 Our results shows that the mixing of Na is effective in promoting the densification of the ceramics and can be well sintered and exhibit a dense, pure perovskite structure and this is attributed to the fact of the presence of oxygen vacancies. For most KNN-based solid solutions, the piezoelectric properties are enhanced but with a reduced Tc [19]. Therefore as 20% mixing of Na, transition temperature is 215oC whereas 40% mixing of Na, transition temperature reduces to 205oC, which shows that transition temperature from orthorhombic to tetragonal shifts towards lower temperature as we increase the quantity of anti ferroelectric material NaNbO3 in the mixed system, K1XNaXNbO3. ACKNOWLEDGEMENTS The authors are thankful to IIT Delhi, NPL Delhi & IIT Roorkee for library facilities and Material Science Research Centre. IIT Madras, for providing laboratory facilities for sample preparation and characterization. Conductivity x 10-6 (1/Kohm-mm) 1600 1400 1200 1000 KNbO3 K0.8Na0.2NbO3 K0.6Na0.4NbO3 800 600 400 200 0 50 70 90 110 130 150 170 190 210 230 Temperature (0C) Figture 3. Variation of electrical conductivity with temperature for K1xNaxNbO3 system at 1 MHz Table 4. Variation of electrical conductivity of K1-xNaxNbO3 with temperature, at 1 MHz frequency Temperature 0C 45 55 65 75 85 95 105 115 125 135 145 155 165 175 185 195 205 KNbO3 (X 10-06) 141 145 147 150 151 152 155 164 188 205 184 182 181 181 181 183 187 K0.8Na0.2NbO3 (X10-6) 250 198 195 255 265 290 278 264 257 276 290 301 310 322 365 498 677 K0.6Na0.4NbO3 (X10-6) 372 299 298 364 422 405 380 349 340 350 366 380 378 369 417 528 707 6. Conclusions REFERENCES [1] Singh K, Lingwal V, Bhatt S C, Panwar N S & Semwal B S,2001, Material Research Bulletin, 36,365-2374 [2] Ahn C W, Song H C et.al.,2005, Japanese Journal of Applied Physics, 44,1361-1364 [3] Ahn C W, Choi C H ,2008, Journal of Material Science, 43,6784-6797 [4] Holman R L, Althouse Johnson L M & Skinner D P,1987, Opt Eng 26, 134 [5] Nystrom M J, Wessels BW, Chen J & Marks T J,1996, Appl Phys Lett 68,761 [6] Hoerman B H, Jichlos B M, Nystrom M J & Wessels B W,1999, Appl Phys Lett 75, 2707 [7] Maeder M D, Damjanovic D, Setter N,2004, Journal of electroceramics 13,385-392 [8] Matthias B T, Remeika J P,1951, Phys Rev 82, 727 [9] Shirane G, Newniham R & Pepinsky R,1954, Phys Rev 96(3), 581 [10] Narayana Murty S, Ramana Murty K V, Umakanthan K & Bhanumati A,1990, Ferroelectrics, 102, 243 [11] Cross L E,1958, Nature, 181, 178 [12] Lin D , Kwok K W and Chan H L W,2007, Journal of Applied Physics 102, 074113 [13] Chu S Y, Water W, Juang Y D & Liaw J T,2003, Ferroelectrics, 287, 23-33 [14] Natl. Bur Stand, (U.S.) Monogr.1980, 25, 17, 62 [15] Katz L & Megaw H D,1967, Acta Crystallogr, 22, 639 50 S C Bhatt et al.: Synthesis, Characterization and Dielectric Properties of K1-xNaxNbO3 [16] Wood E A,1951, Acta Crystallogr. 4, 353 [17] Hearthing G H,1967, J Amer Cerm Soc, 50,330 [18] Shirane G, Newnham R & Pepinsky R, 1954, Phys Rev 96,581 [19] Sun X, Chen J et.al,2009, J.Am.Ceram. Soc., 92[1] 130-132

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