## 3 Results and Discussion
For instance, the maximum densities of 0.9 BaTiO\({}_{3}\)-0.1(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramics with 1.0%, 1.5%, and 2.0% Ta\(\alpha\)O\({}_{5}\) were 5.82, 5.81, and 5.79 g/cm\({}^{3}\), respectively. The results imply that the addition of Ta\(\alpha\)O\({}_{5}\) inhibits the sintering of the host material. As shown in Figure 1b, the sintered densities of 0.9 BaTiO\({}_{3}\)-0.1 Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramics with 1.0%, 1.5%, and 2.0% Nb\(\alpha\)O\({}_{5}\) dopant showed a trend similar to those with added Ta\(\alpha\)O\({}_{5}\). Apparently, both Ta\(\alpha\)O\({}_{5}\) and Nb\(\alpha\)O\({}_{5}\) additives slightly obstructed the densification of the 0.9 BaTi O\({}_{3}\)-0.1(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramic. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Starting Composition**} & \multicolumn{2}{c}{**Sintering**} & \multirow{2}{*}{**Sintered Density (g/cm\({}^{3}\))**} & \multirow{2}{*}{**T\(\mathbf{c}\) (\(\mathbf{C}\))**} & \multirow{2}{*}{**K (25 \(\mathbf{\SIUnitSymbolArcArc{C}}\))**} & \multirow{2}{*}{**tan6 (25 \(\mathbf{\SIUnitSymbolArc{C}}\))**} & \multicolumn{2}{c}{**TCC**} & \multicolumn{2}{c}{**Reastivity \(\mathbf{{}^{+}}\) (\(\Omega\)-cm)**} \\ \cline{4-9}  & **Condition (\(\mathbf{C}\)/h)** & & & & & & & & \\ \hline
0.95 BaTiO\({}_{7}\)\(\sim\)0.05(Bi\({}_{6}\)Na\({}_{0.5}\))TiO\({}_{3}\) & 1230/2 & 5.78 & 145 & 2066 & 2.9\% & \(-\)20.8 & 27.0 & \(4.4\times 10^{12}\) & \(9.2\times 10^{10}\) \\
0.9 BaTiO\({}_{7}\)\(\sim\)0.1(Bi\({}_{6}\)Na\({}_{0.5}\))TiO\({}_{3}\) & 1215/2 & 5.78 & 170 & 1044 & 3.4\% & \(-\)26.2 & 202.0 & \(7.2\times 10^{12}\) & \(1.4\times 10^{11}\) \\
0.8 BaTiO\({}_{7}\)\(\sim\)0.2(Bi\({}_{6}\)Na\({}_{0.5}\))TiO\({}_{3}\) & 1215/2 & 5.82 & \(>\)200 & 677 & 3.5\% & \(-\)24.6 & 641.0 & \(1.9\times 10^{13}\) & \(5.1\times 10^{10}\) \\ \hline \hline \end{tabular}
* Resistivity of the samples was measured at a DC voltage of 500 V.  
\end{table} 
Table 1: Dielectric properties of \((1-x)\)BaTiO\({}_{7}\)=\(x\)(Bi\({}_{6}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramics at their maximum sintered densities. Figure 1: Apparent densities of 0.9 BaTiO\(\sim\)0.1(Bi\({}_{6}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramics with various amounts of (**a**) Ta\(\alpha\)Os and (**b**) Nb\(\alpha\)Os sintered at different temperatures for 2 h.  
Figure 2a shows the XRD patterns of 0.9 BaTiO\({}_{3}\)-0.1(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramics with various amounts of Ta\(\mathrm{\SIUnitSymbolO}\)s sintered at 1215 \(\SIUnitSymbolCelsius\). Only a major phase of tetragonal perovskite was found in the XRD patterns. Several small peaks at around 30\(\SIUnitSymbolDegree\) and 43\(\SIUnitSymbolDegree\) were due to the Ba\({}_{6}\)Ti\({}_{11}\)O\({}_{40}\) phase, which was also observed in the pure 0.9 BaTiO\({}_{3}\)-0.1(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramic. The addition of Ta\({}_{2}\)O\({}_{5}\) in the host material did not trigger any additional second phase, implying that the Ta\(\mathrm{\SIUnitSymbolO}\)s were substituted into the B-sites of the perovskite lattices and the excess Ti\({}^{4+}\) ions caused the formation of the Ba\({}_{6}\)Ti\({}_{11}\)O\({}_{40}\) phase. It was also found that the peaks corresponding to the perovskite phase shifted slightly to lower angles because of the ionic radius of Ta\(\mathrm{\SIUnitSymbolO}\)s\({}^{5+}\) (VI; 0.64 A), which is slightly larger than that of Ti\({}^{4+}\) (VI; 0.605 A). As revealed in Figure 2b, for the 0.9 BaTiO\({}_{3}\)-0.1(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramics with various amounts of added Nb\(\mathrm{\SIUnitSymbolO}  
Overall, it can be concluded that the solubility of Ta\({}_{2}\)O\({}_{5}\) dopant is greater than that of Nb\({}_{2}\)O\({}_{5}\) dopant in the 0.9 BaTiO\({}_{3}\)-0.1(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramic.