## 3 Results and Discussion  
Anatase TiO\({}_{2}\) with a particle size of 80 nm was pre-annealed at a temperature range of 800 to 900 \({}^{\circ}\)C for 1 to 12 h. Characterization of the anatase TiO\({}_{2}\) powder pre-annealed at 800 \({}^{\circ}\)C for 1 h revealed the typical crystal structure of anatase TiO\({}_{2}\). When the pre-annealing time was varied in the range of 3 to 5 h, the fraction of the rutile phase increased, as confirmed via XRD analysis. After pre-annealing at a temperature of 800 \({}^{\circ}\)C for 5 h, anatase-rutile composite TiO\({}_{2}\) powder with 18% rutile TiO\({}_{2}\) was obtained. When the temperature was increased to 850 \({}^{\circ}\)C and the annealing time was increased, a smooth transformation of the anatase to the rutile phase was achieved. After annealing at 900 \({}^{\circ}\)C, an analysis of the resulting crystal structure showed that most of the TiO\({}_{2}\) underwent phase transformation to form rutile TiO\({}_{2}\) within a short annealing time (Figure 1a,b). Therefore, the crystal structure analysis results reveal that controlling the anatase-rutile phase fraction of the composite TiO\({}_{2}\) to form different crystal structures is possible by altering the pre-annealing conditions(Figure 1c). In the subsequent solid-state synthesis of BaTiO\({}_{3}\), TiO\({}_{2}\) samples obtained under pre-annealing conditions #1 to #3 and #5 were used (Figure 1d). The anatase phase of TiO\({}_{2}\) has an unstable crystal structure, and under specific temperature conditions, it spontaneously transforms into rutile TiO\({}_{2}\), which is a stable phase [23; 24; 25; 26; 27]. The crystal structure analysis showed that the phase transformation of the anatase TiO\({}_{2}\) to the crystal structure exhibiting a composite phase with approximately 18% rutile phase occurred under the conditions of annealing at 800 \({}^{\circ}\)C for 5 h (Figure 1). Figure 2 shows the results of the HRTEM analysis of the annealed TiO\({}_{2}\) powder. Grains of larger and smaller sizes were observed in the powder. Fast Fourier transformation (FFT) analysis of the HRTEM images confirmed that the larger grains possessed the anatase crystal structure, whereas smaller grains were rutile phase TiO\({}_{2}\). These observations indicate that when anatase TiO\({}_{2}\) was annealed at the given temperature, small grains could transform to the rutile phase. Mixed powders were prepared by mixing TiO\({}_{2}\) synthesized under different annealing conditions (#1 to #3;#5) with BaCO\({}_{3}\) with a molar ratio of 1:1. In addition, anatase and rutile TiO\({}_{2}\) powders were mixed to ensure that the anatase-rutile phase ratio was the same as that of the heated TiO\({}_{2}\) powder prepared under respective annealing conditions. The prepared TiO\({}_{2}\) powder was mixed with BaCO\({}_{3}\) at a molar ratio of 1:1 to obtain a BaCO\({}_{3}\)-TiO\({}_{2}\) powder. Furthermore, powders were prepared by separately mixing 100% anatase TiO\({}_{2}\) and 100% rutile TiO\({}_{2}\) with BaCO\({}_{3}\) at a molar ratio of 1:1 (Table 1). Figure 1: Analysis of changes in the crystal structure and composite phase ratio according to the heat treatment conditions: (**a**) Anatase TiO\({}_{2}\). (**b**) XRD characterization. (**c**) Anatase-rutile phase ratio under different treatment conditions. (**d**) TiO\({}_{2}\) treatment conditions for the experiment on the solid-state synthesis of BaTiO\({}_{3}\). The BaCO\({}_{3}\)-TiO\({}_{2}\) powders, mixed as described above, were calcined at 1000 and 1100 \({}^{\circ}\)C for 2 h. XRD analysis of the powders obtained via solid-state synthesis at 1000 \({}^{\circ}\)C under respective mixing conditions revealed the presence of typical BaTiO\({}_{3}\) crystal structures.