Physical and Dielectric Properties of Silver Lithium Niobate Mixed Ceramic System

Transcription

1 American Journal of Materials Science and Engineering, 213, Vol. 1, No. 3, Available online at Science and Education Publishing DOI: /ajmse Physical and Dielectric Properties of Silver Lithium Niobate Mixed Ceramic System Om Prakash Nautiyal 1,*, S C Bhatt 2 1 Uttarakhand Science Education and Research Centre (U-SERC), 33-Vasant Vihar, Phase-II, Dehradun, India 2 Department of Physics, H N B Garhwal University, Srinagar, Garhwal, Uttarakhand, India *Corresponding author: nautiyal_ omprakash@yahoo.co.in Received July 11, 213; Revised November 23, 213; Accepted November 24, 213 Abstract The perovskite niobates (ANbO 3 ) constitutes an interesting structural family. Silver lithium niobate Ag 1- xli x NbO 3 (x =,.3,.5 and.7) mixed ceramic pellets were synthesized by the by solid-state reaction and sintering method. The lattice parameters of ceramic pellets were characterized by X-ray diffraction (XRD). The prepared samples show a perovskite structure and exhibit the orthorhombic symmetry at room temperature. Frequency dependent dielectric investigations, i.e., dielectric constant, loss tangent and electrical conductivity were carried out in the frequency range 1Hz-1MHz at room temperature. Keywords: perovskite, silver lithium niobate, ceramic, X-ray diffraction (XRD), dielectric constant, loss tangent, electrical conductivity Cite This Article: Om Prakash Nautiyal, and S C Bhatt, Physical and Dielectric Properties of Silver Lithium Niobate Mixed Ceramic System. American Journal of Materials Science and Engineering 1, no. 3 (213): doi: /ajmse Introduction The constituents of the silver lithium niobate (Ag 1- xli x NbO 3 ) system are silver niobate (AgNbO 3 ) and lithium niobate (LiNbO 3 ). Silver niobate AgNbO 3 undergoes a sequence of phase transitions at 387 C orthorhombic to tetragonal and at 567 C, tetragonal to cubic [1,2]. Lithium niobate LiNbO 3 undergoes the phase transition at 121 C, from the trigonal [Ferroelectric] to the trigonal [Paraelectric]. The non- linear acoustical properties of LiNbO 3 have led to the observation of a new physical effect. An acoustical tone burst stores energy within the crystal that is re emitted at a later time of order of 7 μs. This effect can be characterized as an acoustic memory. This phenomenon is dependent on frequency and temperature [3]. X-ray investigations of Ag 1-x Li x NbO 3 solid solution ceramics ( x.15) showed that small Li substitution causes a change of symmetry [4]. At room temperature, a phase boundary between orthorhombic and rhombohedral symmetry is observed for x =.5; this phase boundary is indicated also by dielectric properties. The Li- substitution, leads to a gradual rise and shift of diffuse ε' (T) maximum which is observed for (AN) as 227 C Instead of this diffuse maximum, a sharp one at 197 C is already observed for Ag.94 Li.6 NbO 3 [4]. In the present study pellets of Ag 1-x Li x NbO 3 (for x =,.3,.5 &.7) were prepared by conventional solid-state reaction method. Characterization of the samples was made by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Dielectric measurements of all the prepared samples were carried out in the different frequency ranges 5Hz to 1Hz;.1KHz to 1KHz and.1mhz to 1MHz, at room temperature. 2. Experimental Details The raw materials, used for preparing compositions, for present study, were silver oxide (Ag 2 O), lithium carbonate (Li 2 CO 3 ), and niobium pentaoxide (Nb 2 O 5 ). Similar to preparation of silver sodium niobate [5,6,7] and silver potassium niobate [8,9,1], the sample of silver lithium niobate was also prepared by conventional sintering method, i.e., solid-state reaction method [11]. Prepared samples were characterized using XRD and SEM. The prepared and sintered pellets of all compositions were gold polished for Scanning Electron Micrographs (SEM) and electroded in metal-insulator-metal (MIM) configuration using air-drying silver paste for dielectric measurements. X-ray diffraction (XRD) pattern of all the samples at room temperature have been obtained on Bruker s D-8 ADVANCE X-ray diffractometer, using Cu-K α filter radiation of Å wavelength. Surface topography of the samples was studied by LEO-44 scanning electron microscope. The dielectric constant, loss tangent and conductivity of the prepared samples were measured and calculated with the help of Solartron 126 Impedance Gain Phase Analyzer. 3. Results and Discussion 3.1. X-ray Diffraction Patterns

2 American Journal of Materials Science and Engineering 55 The X-ray diffraction patterns of Ag 1-x Li x NbO 3 for x =,.3,.5 and.7 obtained from all the prepared samples have been shown in Figure 1, Figure 2, Figure 3, Figure 4. From X-ray patterns, it was found that at room temperature all the compositions show characteristic lines corresponding to the orthorhombic. Lattice parameters (Figure 5) also reveal the structures of present systems. From Scanning Electron Micrographs (SEM), the grain of different sizes with orthorhombic shape grows in the prepared samples of Ag 1-x Li x NbO 3 [12]. Smaller grains occupy the space between the bigger grains, and thus reducing the porosity. Figure 1. X-ray diffraction pattern of AgNbO 3 samples Figure 2. X-ray diffraction pattern of Ag.7Li.3NbO 3 samples Figure 3. X-ray diffraction pattern of Ag.5Li.5NbO 3 samples

3 56 American Journal of Materials Science and Engineering Figure 4. X-ray diffraction pattern of Ag.3Li.7NbO 3 samples value of latice parameter (Α ) a b c Lattice parameters Ag.7Li.3NbO3 Ag.5Li.5NbO3 Ag.3Li.7NbO3 Figure 5. Lattice parameters of different compositions of Ag 1-xLi xnbo 3 samples Dielectric Constant Ag.3 Li.7 NbO Frequency (MHz) Figure 6. Variation of dielectric constant (K) with frequency at room temperature for Ag 1-X Li X NbO 3 system in the high frequency range (.1 MHz to 1 MHz) Dielectric Constant Ag.3 Li.7 NbO Frequency (KHz) Figure 7. Variation of dielectric constant (K) with frequency at room temperature for Ag 1-X Li X NbO 3 system in the frequency range.1 KHz to 1 KHz

4 American Journal of Materials Science and Engineering 57 Dielectric Costant Frequency (Hz) Ag.3 Li.7 NbO3 Figure 8. Variation of dielectric constant (K) with frequency at room temperature for Ag 1-X Li X NbO 3 system in the frequency range 5 Hz to 1 Hz 3.2. Dielectric Properties Dielectric Constant (K) The variation of dielectric constant with frequencies, at room temperature, for different compositions of Ag 1- xli x NbO 3 system, in the different frequency ranges.1 MHz to 1 MHz;.1 KHz to 1 KHz and 5 Hz to 1 Hz has been shown in Figure 6, Figure 7 & Figure 8 respectively. From these figures, it has been observed that at room temperature, dielectric constant slightly decreased with increasing frequency except at higher frequencies, i.e., at 3-1 MHz, where dielectric constant slightly increased. However, dielectric constant decreases with increasing Li content in Ag 1-X Li X NbO 3 in the measured frequency range (1 Hz to 1 MHz), except for x =, i.e., for AgNbO 3, who show the anomalous behavior, in the frequency range 1 KHz to 1 MHz, where it decreased Tangent Loss (tanδ) The variations of tangent loss (tanδ) with frequency, at room temperature, have been shown in Figure 9, Figure 1, Figure 11, in the frequency range 5 Hz to 1 MHz. It has been observed that tangent loss very slightly decrease with increasing frequency and show a small increase for AgNbO 3 at 3 KHz - 3 KHz. However, loss tangent decrease with increasing x- value, i.e., Li contents in Ag 1-X Li X NbO 3, but magnitude of loss tangent for x =.7, is found higher than that for x =.3 and.5, in the frequency range 1 Hz to 1 KHz. Further, tanδ very slightly increase with increasing frequency, and show a small decrease at 1.26 MHz. However, loss tangent decrease with increasing x- value, in Ag 1-X Li X NbO 3, in the frequency range.1mhz to 1MHz, but Ag.7 Li.3 NbO 3 shows anomalous behavior above 6 MHz frequency, where it increases. Tangent Loss Frequency (MHz) Ag.3 Li.7 NbO3 Figure 9. Variation of tangent loss (tanδ) with frequency at room temperature for Ag 1-X Li X NbO 3 system in the high frequency range (.1 MHz to 1 MHz) Tangent Loss Frequency (KHz) Ag.3 Li.7 NbO3 Figure 1. Variation of tangent loss (tanδ) with frequency at room temperature for Ag 1-X Li X NbO 3 system in the frequency range from.1 KHz to 1 KHz

5 58 American Journal of Materials Science and Engineering Tangent Loss Frequency (Hz) Ag.3 Li.7 NbO3 Figure 11. Variation of tangent loss (tanδ) with frequency at room temperature for Ag 1-X Li X NbO 3 system in the low frequency range (5 Hz to 1 Hz) Electrical Conductivity (σ) The variations of electrical conductivity (σ) with frequency, at room temperature, have been shown in Figure 12, Figure 13, Figure 14, in the frequency range 1 Hz to 1 MHz. It has been observed from these figures, that electrical conductivity increases with increasing frequency in all measured frequency range (1 Hz to 1 MHz), with a small decrease at 1.26 MHz. It has also been observed that electrical conductivity decrease as Li content increase, in the frequency range 1 Hz 2 MHz and Ag.7 Li.3 NbO 3 shows anomalous behavior, showing increase, in the frequency range 2 MHz to 1 MHz. The maximum values of electric conductivity have been observed Ω -1 cm -1, Ω -1 cm -1 and Ω -1 cm -1 for x =,.3, and.5, i.e., for AgNbO 3, Ag.7 Li.3 NbO 3 and Ag.5 Li.5 NbO 3 respectively, at 1 MHz frequency. Conductivity (x 1-6 ohm -1 cm -1 ) Frequency (MHz) Figure 12. Variation of conductivity (σ) with frequency at room temperature for Ag 1-X Li X NbO 3 system in the high frequency range from.1 MHz to 1 MHz Conductivity (x 1-9 ohm -1 cm -1 ) Frequency (KHz) Figure 13. Variation of conductivity (σ) with frequency at room temperature for Ag 1-X Li X NbO 3 system in the frequency range from.1 KHz to 1 KHz

6 American Journal of Materials Science and Engineering 59 Conductivity (x 1-9 ohm -1 cm -1 ) Frequency (Hz) Figure 14. Variation of conductivity (σ) with frequency at room temperature for Ag 1-X Li X NbO 3 system in the low frequency range (1 Hz to 1 Hz) 4. Conclusions In the present work, physical and dielectric properties of lithium doped silver niobate perovskite system, Ag 1- xli x NbO 3 for x =,.3,.5 and.7 have been investigated. From characterization of the prepared samples, it has been observed that at room temperature all the compositions are in orthorhombic phase. Frequency variations of dielectric constant, tangent loss and electrical conductivity were measured at room at room temperature in the frequency range 5Hz to 1 MHz. The solid solution of perovskite silver lithium niobate (Ag 1-X Li X NbO 3 ) can be formed over a whole composition range, and thus allowing a high degree of tailorability of physical properties to cover a broad range of technologically important dielectric, piezoelectric, ferroelectric, optoelectronic, optical, electrical, etc. properties. The observations in present study indicate that these systems have tremendous technological potential. Carrying out further careful and systematic studies, with varying composition and preparative conditions, appropriate materials for different industrial and technological applications can be developed out of these systems. Acknowledgements Authors express hearty thanks to Sh. Vijay Kumar Dhaudhiyal, IAS, Director USERC Dehradun and Prof. B. S. Semwal, Ex. Head, Department of Physics, H N B Garhwal University- Srinagar, Srinagar Garhwal, Uttarakhand, India for their help, support & encouragement. References [1] Sciau. Ph., Kania, A., Dkhil, B., Suard, E., Ratuszna, A., J. Phys.: Condens. Matter, 16, 2795, 24. [2] Nautiyal, O.P., Bhatt,S.C. and Bartwal, K.S., J. Alloys Compd., 55, 168, 21. [3] Michael, S., Pherson, Mc, Ostrovskit, I. and Breazeale, M.A., Phys. Rev. Lett.,89 (11), 11556, 22. [4] Nalbandinan, V.B., Medviediev, B.S. and Bieliayev, I.N., Izv AN SSSR: Neorg. Mater., 16, 1819, 198. [5] Nautiyal, Om Prakash, Bhatt, S.C., Pant, R.P., Bourai, A.A., Singh, P.K., Saxena R. and Semwal, B.S., Ind. J. Pure & Appl. Phys., 47, 282, 29. [6] Nautiyal, Om Prakash, Bhatt, S.C., Pant, R.P. and Semwal, B.S., Ind. J. Pure & Appl. Phys., 48, 357, 21. [7] Bhatt, S.C., Nautiyal, Om Prakash and Semwal, B.S., Processes and Characterisation of advanced nanostructured materials, Macmillan Publisher India Ltd, 21, [8] Nautiyal, Om Prakash, Bhatt, S.C. and Semwal, B.S., Ind. J. Pure & Appl. Phys., 47, 719, 29. [9] Nautiyal, Om Prakash, Bhatt, S.C. and Semwal, B.S., Processes and Characterisation of advanced nanostructured materials, Macmillan Publisher India Ltd, 21, 3-8. [1] Nautiyal, O.P. and Bhatt, S.C., American Journal of Condensed Matter Physics, 1 (1), 8-11, 211. [11] Nautiyal, Om Prakash and Bhatt, S.C., DAE-BRNS National Laser Symposium (NLS-2), 212, [12] Nautiyal, O.P. and Bhatt, S.C., American Journal of Materials Science, 1 (1), 1-4, 211.