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Physical and Dielectric Properties of Silver Lithium Niobate Mixed Ceramic System

Om Prakash Nautiyal*, S C Bhatt

Uttarakhand Science Education and Research Centre (U-SERC), 33-Vasant Vihar, Phase-II, Dehradun, India

Abstract: The perovskite niobates (ANbO₃) constitutes an interesting structural family. Silver lithium niobate Ag1-xLixNbO3 (x = 0, 0.3, 0.5 and 0.7) 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 10Hz-10MHz at room temperature.

Keywords: perovskite, silver lithium niobate, ceramic, X-ray diffraction (XRD), dielectric constant, loss tangent, electrical conductivity

Received July 11, 2013; Revised November 23, 2013; Accepted November 24, 2013

Citation: Om Prakash Nautiyal, S C Bhatt, Physical and Dielectric Properties of Silver Lithium Niobate Mixed Ceramic System. American Journal of Materials Science and Engineering, 1 (3). 54-59. January 2013. doi:10.12691/ajmse-1-3-5

1. Introduction

The constituents of the silver lithium niobate (Ag1-xLixNbO₃) system are silver niobate (AgNbO₃) and lithium niobate (LiNbO₃). Silver niobate AgNbO₃ undergoes a sequence of phase transitions at 387°C orthorhombic to tetragonal and at 567°C, tetragonal to cubic [1,2]. Lithium niobate LiNbO₃ undergoes the phase transition at 1210°C, from the trigonal [Ferroelectric] to the trigonal [Paraelectric]. The non- linear acoustical properties of LiNbO₃ 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 70 μs. This effect can be characterized as an ‘acoustic memory’. This phenomenon is dependent on frequency and temperature [3]. X-ray investigations of Ag1-xLixNbO₃ solid solution ceramics (0 ≤ x ≤ 0.15) 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 = 0.05; 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 Ag0.94Li0.06NbO₃ [4].

In the present study pellets of Ag1-xLixNbO₃ (for x = 0, 0.3, 0.5 & 0.7) 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 100Hz; 0.1KHz to 100KHz and 0.1MHz to 10MHz, at room temperature.

2. Experimental Details

The raw materials, used for preparing compositions, for present study, were silver oxide (Ag₂O), lithium carbonate (Li₂CO₃), and niobium pentaoxide (Nb₂O₅). Similar to preparation of silver sodium niobate [5,6,7] and silver potassium niobate [8,9,10], 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 ANCE X-ray diffractometer, using Cu-Kα filter radiation of 1.540598Å wavelength. Surface topography of the samples was studied by LEO-440 scanning electron microscope. The dielectric constant, loss tangent and conductivity of the prepared samples were measured and calculated with the help of ‘Solartron 1260 Impedance Gain Phase Analyzer’.

3. Results and Discussion

3.1. X-ray Diffraction Patterns

The X-ray diffraction patterns of Ag1-xLixNbO3 for x = 0, 0.3, 0.5 and 0.7 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 Ag1-xLixNbO₃ [12]. Smaller grains occupy the space between the bigger grains, and thus reducing the porosity.

Figure 1. X-ray diffraction pattern of AgNbO₃ samples

Figure 2. X-ray diffraction pattern of Ag0.7Li0.3NbO₃ samples

Figure 3. X-ray diffraction pattern of Ag0.5Li0.5NbO₃ samples

Figure 4. X-ray diffraction pattern of Ag0.3Li0.7NbO₃ samples

Figure 5. Lattice parameters of different compositions of Ag1-xLixNbO₃ samples

Figure 6. Variation of dielectric constant (K) with frequency at room temperature for Ag1-X LiX NbO₃ system in the high frequency range (0.1 MHz to 10 MHz)

Figure 7. Variation of dielectric constant (K) with frequency at room temperature for Ag1-X LiX NbO₃ system in the frequency range 0.1 KHz to 100 KHz

Figure 8. Variation of dielectric constant (K) with frequency at room temperature for Ag1-X LiX NbO₃ system in the frequency range 5 Hz to 100 Hz

3.2. Dielectric Properties

3.2.1. Dielectric Constant (K)

The variation of dielectric constant with frequencies, at room temperature, for different compositions of Ag1-xLixNbO₃ system, in the different frequency ranges 0.1 MHz to 10 MHz; 0.1 KHz to 100 KHz and 5 Hz to 100 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 3-10 MHz, where dielectric constant slightly increased. However, dielectric constant decreases with increasing ‘Li’ content in Ag1-XLiXNbO₃ in the measured frequency range (10 Hz to 10 MHz), except for x = 0, i.e., for AgNbO₃, who show the anomalous behavior, in the frequency range 10 KHz to 10 MHz, where it decreased.

3.2.2. Tangent Loss (tanδ)

The variations of tangent loss (tanδ) with frequency, at room temperature, have been shown in Figure 9, Figure 10, Figure 11, in the frequency range 5 Hz to 10 MHz. It has been observed that tangent loss very slightly decrease with increasing frequency and show a small increase for AgNbO3 at 3 KHz - 30 KHz. However, loss tangent decrease with increasing x- value, i.e., ‘Li’ contents in Ag1-XLiXNbO₃, but magnitude of loss tangent for x = 0.7, is found higher than that for x = 0.3 and 0.5, in the frequency range 10 Hz to 100 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 Ag1-XLiXNbO₃, in the frequency range 0.1MHz to 10MHz, but Ag0.7Li0.3NbO3 shows anomalous behavior above 6 MHz frequency, where it increases.

Figure 9. Variation of tangent loss (tanδ) with frequency at room temperature for Ag1-X LiX NbO₃ system in the high frequency range (0.1 MHz to 10 MHz)

Figure 10. Variation of tangent loss (tanδ) with frequency at room temperature for Ag1-X LiX NbO₃ system in the frequency range from 0.1 KHz to 100 KHz

Figure 11. Variation of tangent loss (tanδ) with frequency at room temperature for Ag1-X LiX NbO₃ system in the low frequency range (5 Hz to 100 Hz)

3.2.3. 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 10 MHz. It has been observed from these figures, that electrical conductivity increases with increasing frequency in all measured frequency range (10 Hz to 10 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 10 Hz – 2 MHz and Ag0.7Li0.3NbO₃ shows anomalous behavior, showing increase, in the frequency range 2 MHz to 10 MHz. The maximum values of electric conductivity have been observed 103.0 × 10⁻⁶ Ω⁻¹ cm⁻¹, 306.0 × 10⁻⁶ Ω⁻¹ cm⁻¹ and 91.3 × 10⁻⁶ Ω⁻¹ cm⁻¹ for x = 0, 0.3, and 0.5, i.e., for AgNbO₃, Ag0.7Li0.3NbO3 and Ag0.5Li0.5NbO₃ respectively, at 10 MHz frequency.

Figure 12. Variation of conductivity (σ) with frequency at room temperature for Ag1-X LiX NbO₃ system in the high frequency range from 0.1 MHz to 10 MHz

Figure 13. Variation of conductivity (σ) with frequency at room temperature for Ag1-X LiX NbO₃ system in the frequency range from 0.1 KHz to 100 KHz

Figure 14. Variation of conductivity (σ) with frequency at room temperature for Ag1-X LiX NbO₃ system in the low frequency range (1 Hz to 100 Hz)

4. Conclusions

In the present work, physical and dielectric properties of lithium doped silver niobate perovskite system, Ag1-xLixNbO₃ for x = 0, 0.3, 0.5 and 0.7 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 10 MHz.

The solid solution of perovskite silver lithium niobate (Ag1-XLiXNbO₃) 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

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