preparation and characterization of ceramic samples...

Indian Journal of Pure & Applied Physics Vol. 47, October 2009, pp. 719-724

Preparation and characterization of ceramic samples of Ag1−xKxNbO3

Om Prakash Nautiyal, S C Bhatt & B S Semwal

Department of Physics, H N B Garhwal University, Srinagar, Srinagar Garhwal, Uttarakhand

E-mail: [email protected]

Received 29 September 2008; revised 29 July 2009; accepted 28 August 2009

Ceramic pellets of silver potassium niobate (Ag1−xKxNbO3) system have been prepared by conventional sintering method. The prepared samples are characterized by X-ray diffraction (XRD) and scanning electron micrographs (SEM) techniques. Lattice parameters have been calculated by XRD pattern and grain size has been calculated by SEM. It has been observed that all the prepared samples show orthorhombic structure at room temperature.

Keywords: Ceramics, X-ray diffraction, Scanning electron micrographs

1 Introduction The perovskite compounds are of considerable technological importance, particularly with regard to physical properties such as pyro and piezoelectricity, dielectric susceptibility, linear and non-linear optic effects. Many of these properties are gross effects, varying enormously from one perovskite to another, and the differences in crystal structures are hardly apparent. The changes in physical properties are also remarkable when one system is mixed with another to form a composite system, like, NaNbO3 is antiferro-electric in wide range, but when mixed with a small amount, i.e., 2% (mole) of potassium (K), via solid solution technique with KNbO3, which is ferroelectric (with Tc = 435°C) at sodium (Na) site, NaNbO3

becomes ferroelectric1.

Silver niobate (AgNbO3) is a member of the perovskite niobate. AgNbO3 and NaNbO3 are isostructural antiferroelectric compounds. At room temperature, they exhibit the orthorhombic symmetry with the Pbcm space group. The electro-physical properties of AgNbO3 differ from those of NaNbO3 and KNbO3, which is probably due to the presence of silver ions occupying d-shells near the top of the valence band, in contrast to sodium and potassium2. In the present study, relationship between the physical properties and the structure of Ag1−xKxNbO3 has been found out to understand the salient features responsible for structural changes and changes in their physical properties. The analysis of the results may lead to the development of tailor made materials for industrial and technological applications. 2 Material and Methods

The starting materials used for preparing the composition of silver potassium niobate

(Ag1−xKxNbO3) system were silver oxide (Ag2O), of purity 97% (Qualigens Fine Chemicals); potassium carbonate (K2CO3), purity 99.8% (Qualigens Fine Chemicals); and niobium pentaoxide (Nb2O5), purity 99.9% (Loba Chemie). The sample of silver potassium niobate was prepared by solid-state reaction method and sintering process. The starting materials were initially dried at 200°C for 2 h to remove the absorbed moisture and then quantities of the reagent required to prepare silver sodium niobate were weighed in stoichiometric proportion. All the samples were prepared according to following reaction: (1−x) Ag2O + xK2CO3 + Nb2O5 →

2Ag1−xKxNbO3 + xCO2

Potassium carbonate (K2CO3) is a hygroscopic material and hence due care was taken in its handling during the material formation. Each composition was manually dry grounded into fine powder for two and half hours and then wet mixed using reagent methyl alcohol and pestle for next two and half hours. The mixture was calcined in a silica crucible, in air, at 750, 850 and 950°C each for 2 h respectively for carbonate removal and internal reactions. The pre-sintered mixture was mixed and ground again for 2 h, and then palletized at 3 t pressure, using a palletizer of 11 mm diameter. All pellets of a composition were placed on a silica crucible and sintered in air at 1040-1050°C for 11 h. The sintered pellets were gold polished for characterization (SEM) and electroded using air-drying silver paste for dielectric measurements.

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2.1 Characterization

2.1.1 X-ray diffraction patterns

To characterize the material in the present study, X-ray diffraction pattern of all the samples at room temperature were obtained on a D-8 ADVANCE X-ray diffractometer made by Bruker, using Cu-Kα filter radiation of 1.540598Å wavelength. The instrument is well calibrated with the silicon standard sample. The diffraction data were collected in the 2θ range of 10-70° with a scan step of 0.025° and step time 1s. Peak indexing was done by using Joint Committee on Powder Diffraction Standards (JCPDS) data cards. From the observed diffraction pattern, lattice spacing d was determined, which was used to determine the perovskite lattice parameters. The unit-cell parameters were determined using the WinPLOTR computer software (2005 version), which includes CRYSFIRE and FULLPROF software. The X-ray diffraction patterns obtained from all the prepared samples have been shown in Figs 1-4. The values of change in intensity of reflected X-ray beam with angle of incidence in Ag1−xKxNbO3 systems are presented in Tables 1-4 respectively. The lattice parameters for all the prepared compositions have been presented in Table 5 and the

variation of lattice parameters with compositions is shown in Figs 5 and 6. 2.1.2 Scanning Electron Micrographs (SEM)

Surface topography of the samples was studied by SEM using LEO-440 scanning electron microscope. Figures 7-10 show typical electron micrographs of silver potassium niobate Ag1−xKxNbO3 mixed system. Grain size — Variation of average grain size with the different compositions of Ag1−xKxNbO3 has been shown in Fig. 11 and Table 6. 3 Results and Discussion

X-ray diffraction patterns (XRD) obtained for all prepared samples show characteristic lines corresponding to the orthorhombic along with some impurities and are shown in Figs 1-4. From X-ray patterns, it was found that at room temperature all the compositions are in orthorhombic phase, which is in agreement with the previously reported results3-11. Lattice parameters (Table 5, Figs 5 and 6) also reveal the structures of present systems. The SEM pictures of Ag1−xKxNbO3 samples have been shown in Figs 7-10. The average grain size with the different compositions of Ag1−xKxNbO3 has been given in Table 6 and shown in Fig. 11. The grain of

Fig. 1 — X-ray diffraction pattern of AgNbO3

AgNbO3 (x=0)

NAUTIYAL et al.: CHARACTERIZATION OF CERAMIC SAMPLES OF Ag1−xKxNbO3

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Fig. 2 — X-ray diffraction pattern of Ag0.7K0.3NbO3

Fig. 3 — X-ray diffraction pattern of Ag0.5 K 0.5NbO3

AKN (x=0.3)

AKN (x=0.5)


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Fig. 4 — X-ray diffraction pattern of Ag0.3 K 0.7NbO3

Table 1 — Change in intensity of reflected X-ray beam with angle of incident in AgNbO3

2θ d I h k l

31.93162

32.24039

39.80608

46.00604

46.40102

57.06031

57.48738

57.62886

67.40459

2.8004

2.7743

2.2627

1.9712

1.9553

1.6128

1.6018

1.5982

1.3882

41.4

247.1

12.7

47.7

75.4

19.2

48.5

44.6

28.0

2 0 0

0 2 0

0 2 1

2 2 0

0 0 2

3 1 1

1 3 1

0 2 2

2 2 2

Table 2 — Change in intensity of reflected X-ray beam with angle

of incident in Ag0.7K0.3NbO3

2θ d I h k l

22.724 27.647 30.325 32.128 32.477 46.319 57.880

3.9100 3.2239 2.9451 2.7838 2.7580 1.9586 1.5919

51.0 25.0 34.0 125.0 11.0 12.0 27.0

0 1 1 2 2 0 5 0 1 0 2 1 1 2 1 3 3 1 2 4 1

Table 3 — Change in intensity of reflected X-ray beam with angle of incident in Ag0.5K0.5NbO3

2θ d I h k l 29.270 30.174 31.834 41.867 45.641 56.691 63.143

3.0479 2.9595 2.8088 2.1560 1.9861 1.6221 1.4711

103.0 40.0 158.0 18.0 29.0 42.0 11.0

4 1 0 2 2 1 3 1 1 5 3 0 6 2 0 7 1 1 8 3 0

Table 4 — Change in intensity of reflected X-ray beam with angle of incident in Ag0.3K0.7NbO3

2θ d I h k l

22.473 27.625 29.242 31.700 38.168 40.777 44.384

3.9531 3.2264 3.0516 2.8204 2.3560 2.2111 2.0394

20.0 78.0 30.0 100.0 60.0 24.0 30.0

1 1 1 2 3 0 2 2 1 1 3 1 3 3 1 1 0 2 5 3 0

Table 5 — Lattice parameters of Ag1−xKxNbO3 for different x values

Lattice Parameters Compositions a (Å) b (Å) c (Å)

AgNbO3 Ag0.7 K0.3 NbO3 Ag0.5 K0.5 NbO3

Ag0.3 K0.7 NbO3

5.5972 18.7492 12.5705 12.0777

5.5423 6.8689 12.5705 11.4185

3.9100 4.7578 3.9688 4.4974

AKN (x=0.7)

NAUTIYAL et al.: CHARACTERIZATION OF CERAMIC SAMPLES OF Ag1−xKxNbO3

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Fig. 5 — Effect of K on the lattice parameters of AgNbO3

Fig. 6 — Lattice parameters of different compositions of Ag1-x K xNbO3

Fig. 7 — Scanning Electron Micrographs of AgNbO3

Fig. 8 — Scanning Electron Micrographs of Ag0.7K0.3NbO3



Fig. 11 — Variation of average grain size with the different compositions of Ag1-x K xNbO3

Table 6 — Variation of average grain size with the different

compositions of Ag1−xKxNbO3

Compositions Grain size (µm )

AgNbO3 Ag0.7 K0.3 NbO3

Ag0.5 K0.5 NbO3

Ag0.3 K0.7 NbO3

5.127 3.588 3.415 3.144


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different sizes with orthorhombic shape grow in the prepared samples of Ag1−xKxNbO3 for x = 0, 0.3, 0.5 and 0.7. Smaller grains occupy the space between the bigger grains, and thus reducing the porosity. Some of the grains grow in laminar shape (~ 3 to 7 µm lengths and ~ 1.5 to 2.5 µm lateral sizes). 4 Conclusions

From XRD and SEM studies, it has been observed that all the prepared samples show orthorhombic structure at room temperature. It has also been observed that for composition Ag0.7K0.3NbO3 average grain size decreases. As K is lighter and smaller than Ag, it causes a decrease in average grain size and on further increasing the concentration of K the value of average grain size decreased. Acknowledgement

Authors are thankful to Institute of Instrumentation Centre (IIC), IIT Roorkee, and National Physical

Laboratory, New Delhi for providing laboratory facilities for XRD and SEM.

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27. 4 Kania A, J Phys D: Appl Phys, 34 (2001) 1447. 5 Valant M, Axelsson A K & Alford N, J Eur Ceram Soc, 27

(2007) 2549. 6 Fabry J, Zikmund Z, Kania A & Petricek V, Acta Cryst, C 56

(2000) 916. 7 Kania A & Kwapuliniski J, J Phys: Condens Matter,

11(1999) 8933. 8 Wada S, Saito A, Hoshina T, et al., Japan. J Appl Phys, 45

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