**8. Conclusion**

374 Sintering of Ceramics – New Emerging Techniques

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.

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 antenna applications.
