**7.2 Effect of Sm3+ and Pr3+ doping on grain orientation**

The preferred grain orientation was obviously affected by rare-earth doping in BTO particularly after sintering. Kannan et al. (Kannan et al., 2006) reported the reflections corresponding to (00*l*) plane along the *c*-axis was observed with increasing Nd3+ content from 0 to 0.25. It can give us another hint that preferred grain orientation would be different when rare-earth was introduced into BTO lattice. As discussed in **Figure 6**, the pure BTO was formed with no preferred grain orientation. In **Figure 7**, the XRD patterns of BST and BPT ceramics sintered at 1100oC for 3 hour were presented. As seen from this figure, the Sm3+ and Pr3+ doping show a highly *c*-axis oriented growth with increasing Sm3+ and Pr3+ contents. The XRD peak corresponding to (00*l*) plane was clearly observed with higher intensity as compared to (117) plane. To simplify the discussion, the peak at (0014) and (117) are taken into consideration to determine the degree of *c*-axis orientation, α*c* by Lotgering factor (Yang et al., 2008):

$$\alpha\_c = I(00\underline{14}) / \left[ I(00\underline{14}) + I(117) \right]$$

The values of α*c* calculated for the Sm3+ and Pr3+ doping with various contents are listed in **Table 5**. It was found that the degree of *c*-axis orientation increased with increasing Sm3+ and Pr3+ content. This indicates that the doping content has a significance result on grain orientation.


Table 5. Lotgering factor of the degree of *c*-axis orientation.

Sintering and Characterization of Rare Earth Doped

(e) BPrT:1.0, sintered at 1100oC for 3 hour.

in a such way.

Bismuth Titanate Ceramics Prepared by Soft Combustion Synthesis 371

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

Fig. 8. FESEM micrograph of (a) BTO, (b) BSmT:025, (c) BSmT:1.0, (d) BPrT:025 and

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

Fig. 7. XRD patterns of (a) BSmT and (b) BPrT ceramics sintered at 1100oC for 3 hour.

#### **7.3 Microstructure of bulk ceramics after sintering**

It is more interesting to observe the microstructure of bulk ceramics after sintering, as shown in **Figure 8**. Prior to view the micrograph using field emission scanning electron microscopy (FESEM), the surface of ceramics were polished on SiC papers grit 1000 followed by finer grit 2000. The polished ceramics were placed into ultrasonic for 10 minute to remove contaminants. The polished ceramics were thermally etched with temperature of 100oC lower than the sintering temperature for 30 minute. As can be seen in **Figure 8a**, the microstructure of the BTO ceramic shows a random arrangement of elongated-like grains, several of which are highly elongated. On the other hand, the microstructure of the BSmT and BPrT ceramics show a random arrangement of plate-like grains, as observed in **Figure 8b-8e**. It was also noticed that the average grain size relatively decrease with increasing Sm3+ and Pr3+ contents, indicating a strong influence of doping concentration which resulted in less amount of Bi3+ in BTO. The micrographs also revealed that the plate-like grains were not homogeneously distributed when Sm3+ and Pr3+ are equivalent to 0.25. Nevertheless, homogeneous microstructures with small grain size were found from the BSmT and BPrT ceramics with 1.0. The resultant micrographs was mainly attributed to a greater suppresion of the Bi3+ volatility by substitution of low diffusivity of Sm3+ and Pr3+, which eventually inhibits the grain growth.

Fig. 7. XRD patterns of (a) BSmT and (b) BPrT ceramics sintered at 1100oC for 3 hour.

It is more interesting to observe the microstructure of bulk ceramics after sintering, as shown in **Figure 8**. Prior to view the micrograph using field emission scanning electron microscopy (FESEM), the surface of ceramics were polished on SiC papers grit 1000 followed by finer grit 2000. The polished ceramics were placed into ultrasonic for 10 minute to remove contaminants. The polished ceramics were thermally etched with temperature of 100oC lower than the sintering temperature for 30 minute. As can be seen in **Figure 8a**, the microstructure of the BTO ceramic shows a random arrangement of elongated-like grains, several of which are highly elongated. On the other hand, the microstructure of the BSmT and BPrT ceramics show a random arrangement of plate-like grains, as observed in **Figure 8b-8e**. It was also noticed that the average grain size relatively decrease with increasing Sm3+ and Pr3+ contents, indicating a strong influence of doping concentration which resulted in less amount of Bi3+ in BTO. The micrographs also revealed that the plate-like grains were not homogeneously distributed when Sm3+ and Pr3+ are equivalent to 0.25. Nevertheless, homogeneous microstructures with small grain size were found from the BSmT and BPrT ceramics with 1.0. The resultant micrographs was mainly attributed to a greater suppresion of the Bi3+ volatility by substitution of low diffusivity of Sm3+ and Pr3+, which eventually

**7.3 Microstructure of bulk ceramics after sintering** 

inhibits the grain growth.

Fig. 8. FESEM micrograph of (a) BTO, (b) BSmT:025, (c) BSmT:1.0, (d) BPrT:025 and (e) BPrT:1.0, sintered at 1100oC for 3 hour.
