## 3 Results and Discussion
The rutile phase is also a tetragonal structure and presents diffraction peaks at 20 = 27.4\({}^{\circ}\), 36.1\({}^{\circ}\), 39.2\({}^{\circ}\), 41.2\({}^{\circ}\), 44.0\({}^{\circ}\), 54.3\({}^{\circ}\), 56.6\({}^{\circ}\), 62.7\({}^{\circ}\), 64.0\({}^{\circ}\), 69.0\({}^{\circ}\), and 69.8\({}^{\circ}\) corresponding to (110), (101), (200), (111), (210), (211), (220), (002), (310), (301), and (112) planes, respectively (JCPDS card no. 21-1276). Orthorhombic as shown in the brookite phase presents diffraction peaks at 20 = 25.3\({}^{\circ}\), 25.7\({}^{\circ}\), 36.2\({}^{\circ}\), 42.3\({}^{\circ}\), 55.2\({}^{\circ}\) and 57.2\({}^{\circ}\) corresponding to (120), (111), (012), (221), (241), and (113) planes, respectively (JCPDS card no. 29-1360). The broader peaks of XRD patterns were observed before calcination and after calcination from 300 \({}^{\circ}\)C to 500 \({}^{\circ}\)C. This could be attributed to high amorphous structure of TiO\({}_{2}\). Increasing calcination temperature above 600 \({}^{\circ}\)C, it was found that the crystallinity of TiO\({}_{2}\) increased due to the sharper and narrower peaks of XRD patterns. The crystallinity increased with increasing calcination temperature since higher ordering of the structure of TiO\({}_{2}\) particles leads to the sharper and narrower X-ray peaks. Besides, the crystallite size of all phases increased with increasing calcination temperature which indicates that the crystallization of TiO\({}_{2}\) was improved as shown in Table 1. These results from XRD also confirm and agree well with the TEM results as previously mentioned. Therefore, calcination temperature promoted phase transition, crystallite size, and crystallinity of TiO\({}_{2}\) powder. Figure 2: Transmission electron microscope (TEM) images and selected area electron diffraction (SAED) (inset) images of each TiO\({}_{2}\) particles calcined at (**a**) 300 \({}^{\circ}\)C, (**b**) 600 \({}^{\circ}\)C, (**c**) 700 \({}^{\circ}\)C, and (**d**) 800 \({}^{\circ}\)C.  
The weight percentage of anatase, rutile, and brookite phases of synthesized TiO\({}_{2}\) by different calcination temperatures was estimated by TOPAS. The relationship between calcination temperature and percentage of phase content is shown in Figure 4a. When calcination temperature was increased from 300 \({}^{\circ}\)C to 600 \({}^{\circ}\)C, the anatase phase increased from 29% to 42%wt. whereas the brookite phase decreased from 71% to 28%wt. It is interesting to note that the brookite phase was observed at calcination temperature below 600 \({}^{\circ}\)C. It was reported that the brookite phase can be observed as a by-product in the sol-gel method in an acidic condition at low temperature [27]. These results corresponded well with other studies as shown in Table 2. There was a mixture of anatase and brookite phases when calcination temperature was increased from 300 \({}^{\circ}\)C to 400 \({}^{\circ}\)C. This result was correlated with the study of [PERSON] et al. [26]. Considering calcination temperature between 600 \({}^{\circ}\)C and 700 \({}^{\circ}\)C, it was observed that the anatase phase decreased from 42% to 38%wt. whereas the rutile phase increased from 30% to 62%wt. The rutile phase was observed above 500 \({}^{\circ}\)C. This result was in good agreement with the results of the previous studies.