**7.4 Effect of sintering temperature and Sm3+, Pr3+ content on relative density**

The effect of sintering temperature on relative density of BTO ceramics was studied and depicted in **Figure 9a**. With increasing temperature, the relative density of ceramics was also increased up to 93% at 1100oC. This indicates that the densification behavior of BTO ceramics is temperature dependent. Thus, the sintering temperature at 1100oC was used for densification process with doping content. **Figure 9b** and **Figure 9c** show the relative density of Sm3+ and Pr3+ doping, respectively. As seen, the densities of BTO with doping content are different from one to another. It was determined that the densities was in range of 92 - 95%, indicating that a slight improvement as compared to pure BTO. The increase in relative density is associated to the decrease in Bi-loss during sintering resulting from the substitution effect by Sm3+ and Pr3+. It can be said the small difference in relative density is another indicator to show the improvement of densification behavior in a such way.

Sintering and Characterization of Rare Earth Doped

and (b) BPrT.

**BPrT ceramics** 

range at room temperature.

Bismuth Titanate Ceramics Prepared by Soft Combustion Synthesis 373

stable resonant frequency coefficient (Lazarević et al., 2005). Thus, this study is essential to determine the potential application of such a field for the BTO, BSmT and BPrT ceramics.

 Fig. 10. Dielectric constant, εr and dielectric loss, tan δ at different doping contents: (a) BSmT

**7.6 Effect of various frequencies on the dielectric properties of the BTO, BSmT and** 

As reported in previous studies, the dielectric constant, εr and dielectric loss, tan δ were strongly dependent on frequency (Rachna et al., 2010, Simões et al., 2008). In this work, the dielectric poperties were measured at different frequency ranges from 1 MHz to 1 GHz. As it can be seen from **Figure 11**, the εr of the BTO ceramic shows very obvious dispersion with

Fig. 11. Dielectric constant, εr of (a) BTO, (b) BSmT and (c) BPrT measured at high frequency

Fig. 9. Relative density of (a) BTO at different sintering temperatures, (b) BSmT with different Sm3+ contents and (c) BPrT with different Pr3+ contents; sintered at 1100oC.

#### **7.5 Effect of Sm3+ and Pr3+ doping on dielectric properties**

The effect of Sm3+ and Pr3+ contents in BSmT and BPrT on dielectric properties were studied. In this study, the measurement of dielectric constant, εr and dielectric loss, tan δ were performed at 1 kHz and at room temperature, 25oC and the results were presented in **Figure 10**. The variation of εr and tan δ were clearly observed in **Figure 10a** and **Figure 10b** for the BSmT and BPrT ceramics, respectively. The εr of the BSmT ceramics were in the range between 78 and 95, whereas the εr of the BPrT ceramics were in the range between 75 an 105. This indicates that the εr of the BPrT ceramics was slightly larger than the BSmT ceramics. This is associated to the larger ionic radii of Pr3+ than that of Sm3+. This result can be explained by a shift of TiO6 octahedra in a layered structure due to the substitution of larger ionic radii than that of Bi3+. It was also noticed that the tan δ abruptly decreased with increasing Sm3+ and Pr3+ contents from 0.25 to 0.5. The decrement in the tan δ was attributed to a better electric flux caused by the reduction of grain imperfection. It was also supported by the increase in relative density, in which the ceramics appeared to be dense. Above 0.5, the tan δ were almost consistent with small difference in its value, corresponding to the reduction of the defects such as bismuth and oxygen vacancies. In order to see possible application as dielectric antenna, the dielectric study at different frequencies was performed. It was reported that the development of wireless technologies application requires very stringent criteria for dielectric ceramics materials. Typically, the dielectric ceramic materials must have a high dielectric constant, low dielectric loss and a a thermally

Fig. 9. Relative density of (a) BTO at different sintering temperatures, (b) BSmT with different Sm3+ contents and (c) BPrT with different Pr3+ contents; sintered at 1100oC.

The effect of Sm3+ and Pr3+ contents in BSmT and BPrT on dielectric properties were studied. In this study, the measurement of dielectric constant, εr and dielectric loss, tan δ were performed at 1 kHz and at room temperature, 25oC and the results were presented in **Figure 10**. The variation of εr and tan δ were clearly observed in **Figure 10a** and **Figure 10b** for the BSmT and BPrT ceramics, respectively. The εr of the BSmT ceramics were in the range between 78 and 95, whereas the εr of the BPrT ceramics were in the range between 75 an 105. This indicates that the εr of the BPrT ceramics was slightly larger than the BSmT ceramics. This is associated to the larger ionic radii of Pr3+ than that of Sm3+. This result can be explained by a shift of TiO6 octahedra in a layered structure due to the substitution of larger ionic radii than that of Bi3+. It was also noticed that the tan δ abruptly decreased with increasing Sm3+ and Pr3+ contents from 0.25 to 0.5. The decrement in the tan δ was attributed to a better electric flux caused by the reduction of grain imperfection. It was also supported by the increase in relative density, in which the ceramics appeared to be dense. Above 0.5, the tan δ were almost consistent with small difference in its value, corresponding to the reduction of the defects such as bismuth and oxygen vacancies. In order to see possible application as dielectric antenna, the dielectric study at different frequencies was performed. It was reported that the development of wireless technologies application requires very stringent criteria for dielectric ceramics materials. Typically, the dielectric ceramic materials must have a high dielectric constant, low dielectric loss and a a thermally

**7.5 Effect of Sm3+ and Pr3+ doping on dielectric properties** 

stable resonant frequency coefficient (Lazarević et al., 2005). Thus, this study is essential to determine the potential application of such a field for the BTO, BSmT and BPrT ceramics.

Fig. 10. Dielectric constant, εr and dielectric loss, tan δ at different doping contents: (a) BSmT and (b) BPrT.

#### **7.6 Effect of various frequencies on the dielectric properties of the BTO, BSmT and BPrT ceramics**

As reported in previous studies, the dielectric constant, εr and dielectric loss, tan δ were strongly dependent on frequency (Rachna et al., 2010, Simões et al., 2008). In this work, the dielectric poperties were measured at different frequency ranges from 1 MHz to 1 GHz. As it can be seen from **Figure 11**, the εr of the BTO ceramic shows very obvious dispersion with

Fig. 11. Dielectric constant, εr of (a) BTO, (b) BSmT and (c) BPrT measured at high frequency range at room temperature.

Sintering and Characterization of Rare Earth Doped

of ceramic.

**8. Conclusion** 

antenna applications.

**9. Acknowledgment** 

**10. References** 

(2008) 44.

Society, 89 (2006) 3340.

Ceramic Society, 89 (2006) 490.

Bismuth Titanate Ceramics Prepared by Soft Combustion Synthesis 375

Therefore, the BSmT and BPrT with 1.0 gave a lower dielectric loss at relaxation frequency due to the above reason. Besides that, the improved εr with little dispersion and small variation in tan δ (or almost constant) can also suggest that the BSmT and BPrT ceramics are possible to be applied for wireless dielectric antenna applications instead of the BTO ceramic. However, a detail study is necessary to focus on return loss with a specific design

Based on this work, the rare-earth doping i.e. Sm3+ and Pr3+ had successfully improved the processing and properties of pure BTO ceramics. The calcination temperature was greatly reduced from 750oC to 650oC in order to form a single phase structure. The particle size of plate-like structure decreased continuously with increasing Sm3+ and Pr3+ content. The peak intensity and peak width in Raman spectrum were apparently low and broaden with increasing Sm3+ content. The Lotgering factor showed the enhancement in degree of *c*-axis orientation. The microstructure of the Sm3+ and Pr3+ doping showed a random arrangement of plate-like grains in which the grain size was relatively decrease at higher doping content. A great in densification behavior was also observed with Sm3+ and Pr3+ doping which resulted in the relative density of about 92-95% at 1100oC. The dielectric constant, εr of the BPrT ceramics was slightly larger than the BSmT ceramics, which can be explained in terms of larger ionic radii of Pr3+ than that of Sm3+. The dielectric loss, tan δ of the BSmT and BPrT ceramics were greatly improved when dopant content above 0.5. For frequency study, the the εr of the BSmT and BPrT ceramics show very little dispersion from 1 MHz to 100 MHz instead of above 100 MHz. The relaxation peak in tan δ was observed approximately 700 MHz for all ceramics with different dopant contents. Based of frequency study, the BSmT and BPrT can be used as potential wireless dielectric

The authors appreciate the technical support from the School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia. This research was supported by the USM

Algueró, M., Ferrer, P., Vila, E., Iglesias, J. E. & Castro, A., Journal of the American Ceramic

Aruna, S. T. & Mukasyan, A. S., Current Opinion in Solid State and Materials Science, 12

Besland, M. P., Djani-Ait Aissa, H., Barroy, P. R. J., Lafane, S., Tessier, P. Y., Angleraud, B., Richard-Plouet, M., Brohan, L. & Djouadi, M. A., Thin Solid Films, 495 (2006) 86. Chen, W., Kinemuchi, Y., Watari, K., Tamura, T. & Miwa, K., Journal of the American

Short term grant 6035276, USM-RU grant 1001/PBahan/8042018 and 811069.

Armstrong, R. A. & Newnham, R. E., Materials Research Bulletin, 7 (1972) 1025.

frequency, indicating that the corresponding ceramic possess high defect concentration such as bismuth and oxygen vacancies. On the other hand, the εr of the BSmT and BPrT ceramics show very little dispersion from 1 MHz to 100 MHz. However, the εr shows very obvious dispersion above 100 MHz. This indicates the εr will be more complex at higher frequency range between 100 MHz and 1 GHz. The dielectric loss, tan δ at different frequencies was depicted in **Figure 12**. It was found that the tan δ of was slowly increased from 1 MHz to 10 MHz and abruptly increased from 10 MHz to 1 GHz, as shown in **Figure 12a**. In addition, the presence of relaxation peak in the tan δ was observed, as shown in inset **Figure 12a**. This indicates that the relaxation peak was observed approximately 700 MHz. It can be said that the increase trend in tan δ was also found in the BSmT and BPrT ceramics, as shown in **Figure 12b** and **Figure 12c**, respectively. Furthermore, the relaxation peaks in the tan δ was also observed around 700 MHz, which is almost comparable to BTO ceramic. The dielectric loss relaxation peak phenomenon can be explained by the Debye-like model for relaxation effects. The dielectric loss peak is maximal at the resonant frequency, which is the reciprocal of the relaxation time (Sulaiman et al., 2010). The dielectric loss relaxation may be generated by several possible factors such as surface roughness, distribution grain sizes and many more (Sulaiman et al., 2010, Wang et al., 2010). From the FESEM micrographs (see **Figure 8c to Figure 8e**) revealed that BSmT and BPrT with 1.0 have homogeneous distribution of grain sizes compared to 0.25.

Fig. 12. Dielectric loss, tan δ of (a) BTO, inset showing the Debye relaxation effect, (b) BSmT and (c) BPrT measured at high frequency range at room temperature.

Therefore, the BSmT and BPrT with 1.0 gave a lower dielectric loss at relaxation frequency due to the above reason. Besides that, the improved εr with little dispersion and small variation in tan δ (or almost constant) can also suggest that the BSmT and BPrT ceramics are possible to be applied for wireless dielectric antenna applications instead of the BTO ceramic. However, a detail study is necessary to focus on return loss with a specific design of ceramic.
