## 3 Results and Discussion
### Phase Transition of Zinc Titanate Precursor Powders calcined at Various Temperatures for 1 h  
Figure 2 shows the XRD patterns of the zinc titanate precursor powders prepared without a dispersant agent or mineralizer and calcined at various temperatures for 1 h. The XRD pattern of the freeze dried precursor powders before calcination is shown in Figure 2(a), which reveals that the precursor powders still maintained the amorphous state. Figure 2(b) shows the XRD pattern of the zinc titanate precursor powders calcined at 600 \({}^{\circ}\)C for 1 h, and indicates that the anatase TiO\({}_{2}\) appeared due to the reflections located (101), (110), (103), (200), (105), (211) and (220) (JCPDS Cards No.89-4203). Figure 2(b) also shows the presence of ZnO, due to the reflection peaks located at (100), (110) and (103) (JCPDS Card No.89-1397). Furthermore, the reflection peaks of Zn\({}_{2}\)Ti\({}_{3}\)O\({}_{8}\) also appeared at (210), (220), (400), (440), and (622) (JCPDS Card No.87-1991). The XRD pattern of zinc titanate precursor powders calcined at 700 \({}^{\circ}\)C for 1 h are illustrated in Figure 2(c), which reveals that the crystallized phases were composed of the major phases of ZnO and Zn\({}_{2}\)Ti\({}_{3}\)O\({}_{8}\), with rutile TiO\({}_{2}\) as the secondary phase and the minor phases of ZnTiO\({}_{3}\) and anatase TiO\({}_{2}\). Figure 2(d) shows the XRD pattern of zinc  
Figure 1: Differential thermal analysis (DTA) curve of zinc titanate precursor powders with a heating rate of 10 \({}^{\circ}\)C\(\cdot\)min\({}^{\text{-1}}\). titanate precursor calcined at 900 \({}^{\circ}\)C for 1 h. It reveals that the crystallized phase was composed of ZnO, Zn\({}_{2}\)TiO\({}_{4}\), rutile TiO\({}_{2}\) and ZnTiO\({}_{3}\), but the anatase TiO\({}_{2}\) disappeared. Moreover, from Figure 2(c) and (d), it is seen that there is a significantly higher intensity value for the ZnO (100) reflection (I\({}_{100}\)). [PERSON] _et al_. [21] have pointed out that for hydrothermal treatment systems, samples reveal an apparent preferential orientation growth in the (100) direction, leading to a significant I\({}_{100}\) value. In fact, zinc and oxygen atoms are arranged alternatively along the c-axis, and thus as is well established, this inherent asymmetry along the c-axis results in the anisotropic growth of ZnO crystallites. On the other hand, [PERSON] and [PERSON] [5] pointed out that with a sample prepared at the mole ratio of ZnO:TiO\({}_{2}=2\):1 and calcined at 700 and 800 \({}^{\circ}\)C for various times, the phase of defect-spinel type Zn\({}_{2}\)Ti\({}_{3}\)O\({}_{8}\) with a trace amount of uncombined TiO\({}_{2}\) is produced. This is caused by the four Ti ions that are missing from the 16-point positions of the spinel-type structure arrangement, resulting in a defective spinel-type structure. Mr \(\check{\rm o}\)ek _et al_. [22] reported that the TiO\({}_{2}\) and Zn\({}_{2}\)TiO\({}_{4}\) are decomposed from prepared Zn\({}_{x}\)Ti\({}_{y}\)O\({}_{z}\) powders for various ratios of ZnO/TiO\({}_{2}\). TiO\({}_{2}\) exists at temperatures of 400-600 \({}^{\circ}\)C prepared by sol-gel method [23]. In Figure 2(b) and (c), it can be seen that although the intensity of Zn\({}_{2}\)Ti\({}_{3}\)O\({}_{8}\) increases with the calcination temperature, a small fraction of Zn\({}_{2}\)Ti\({}_{3}\)O\({}_{8}\) decomposes and leads to the formation of the ZnTiO\({}_{3}\) and rutile TiO\({}_{2}\). This reaction can be expressed as follows:  
\[\rm{Zn_{2}T_{3}O_{8}}\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\! \longrightarrow 2 ZnTiO_{3}+TiO_{2(r)}. \tag{1}\]  
[PERSON] and [PERSON] [24] also pointed out that Zn\({}_{2}\)Ti\({}_{3}\)O\({}_{8}\) is a thermodynamically stable compound up to temperatures between 700 and 800 \({}^{\circ}\)C. Just above this temperature, ZnTiO\({}_{3}\) is more stable than the compound of Zn\({}_{2}\)Ti\({}_{3}\)O\({}_{8}\). Furthermore, [PERSON] _et al_.