## 3 Results and Discussion
By analyzing the diffractions from the (002) and (200) planes of the synthesized BaTiO\({}_{3}\) powders, a structure closely resembling a cubic structure, without distinct peak splitting of the (002) and (200) planes, was confirmed for the BaTiO\({}_{3}\) powder obtained via solid-state synthesis using 100% anatase TiO\({}_{2}\) and 100% rutile TiO\({}_{2}\), respectively (Figure 3a,b). In addition, observing clear 002/200 peak splitting was difficult in the case of the BaTiO\({}_{3}\) powder synthesized using a simple mixture of anatase and rutile TiO\({}_{2}\) powders. However, in the XRD patterns of the BT#1 to BT#4 powders synthesized using the composite TiO\({}_{2}\) powder prepared under the annealing conditions of #1 to #4, apparent 002/200 peak splitting appeared. In the case of BaTiO\({}_{3}\) powders BT#1 to BT#4 synthesized at a temperature of 1100 \({}^{\circ}\)C, apparent peak splitting was observed on the 002/200 planes. \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{2}{c}{**TiO\({}_{2}\)**} \\ \cline{2-3}  & **BT\#1** & \#1 \\ \cline{2-3}
**Heated TiO\({}_{2}\)** & **BT\#2** & \#2 \\ \cline{2-3}  & **BT\#3** & \#3 \\ \cline{2-3}  & **BT\#4** & \#5 \\ \hline \multirow{4}{*}{**Mixed TiO\({}_{2}\)**} & **BT\#5** & A:R = 82:18 \\ \cline{2-3}  & **BT\#6** & A:R = 65:35 \\ \cline{2-3}  & **BT\#7** & A:R = 41:59 \\ \cline{2-3}  & **BT\#8** & A:R = 13:87 \\ \hline \multirow{2}{*}{**Ref.**} & **BT(A)** & Anatase TiO\({}_{2}\) \\ \cline{2-3}  & **BT(R)** & Rutile TiO\({}_{2}\) \\ \hline \end{tabular}
\end{table} 
Table 1: Composition of prepared powders for the solid-state synthesis of BaTiO\({}_{3}\). Figure 2: HRTEM and FFT analysis of TiO\({}_{2}\) powder annealed at 850 \({}^{\circ}\)C for 3 h: (**a–c**) HRTEM analysis results, (**d**) FFT analysis result of TiO\({}_{2}\) powder annealed at 850 \({}^{\circ}\)C for 3 h (Area 1), (**e–g**) HRTEM analysis results, and (**h**) FFT analysis result of TiO\({}_{2}\) powder annealed at 850 \({}^{\circ}\)C for 3 h (Area 2). However, 002/200 peak splitting was not apparent in the case of the BT#5 to BT#8 powders, which used the simply mixed TiO\({}_{2}\) powder. Tetragonality (c/a ratio) means the ratio of the a-axis lattice constant to the c-axis lattice constant. Tetragonality is the source of the high dielectric properties of BaTiO\({}_{3}\) and is one of the important criteria used to evaluate ferroelectric BaTiO\({}_{3}\) powder. The a-axis and c-axis lattice constants were obtained by calculating the (200) and (002) peaks between 44 and 46\({}^{\circ}\) (20) of the measured XRD pattern using Rietveld analysis [28; 29]. Rietveld refinement of the XRD results revealed that the BaTiO\({}_{3}\) powders synthesized using composite TiO\({}_{2}\) powders at 1000 and 1100 \({}^{\circ}\)C had excellent tetragonality values of 1.0094-1.01 (1000 \({}^{\circ}\)C) and 1.0102-1.0104 (1100 \({}^{\circ}\)C), respectively (Figure 4). However, when mixed TiO\({}_{2}\) was used for the synthesis, the resulting powders exhibited low tetragonality values of 1.0048-1.0076 (1000 \({}^{\circ}\)C) and 1.0077-1.0087 (1100 \({}^{\circ}\)C). Figure 3: Characterization of crystal structures of BaTiO\({}_{3}\) powders prepared via solid-state synthesis under different TiO\({}_{2}\) conditions at two different temperatures: (**a**,**b**) 1000 \({}^{\circ}\)C \(\times\) 2 h and (**c**,**d**) 1100 \({}^{\circ}\)C \(\times\) 2 h.  
First, a solid-state synthesis reaction was performed at 1000 \({}^{\circ}\)C under the mixing conditions of BT(A) and BT(R). Microstructure observations conducted after the synthesis under the respective conditions revealed grain growth of the BaTiO\({}_{3}\) powders (Figure 5). The low tetragonality, as indicated by the XRD analysis results, is attributed to the lack of sufficient grain growth [30,31]. Furthermore, grain growth of the BaTiO\({}_{3}\) powders was confirmed when the solid-state synthesis was performed at 1000 \({}^{\circ}\)C under the mixing conditions of BT#1 to BT#4.