## 3 Results and Discussion
The addition of Ta\({}_{2}\)O\({}_{5}\) resulted in the lattice expansion of 0.9 BaTiO\({}_{3}\)-0.1(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramic and reduced the grain boundary mobility and thus slightly inhibited the densification. The average grain size slightly decreased and the number of trapped pores increased with increase of Ta\({}_{2}\)O\({}_{5}\) content. In addition to the pre-existing Ba\(\epsilon\)Ti\(\gamma\)O\({}_{40}\) phase, the escalation in addition of Nb\({}_{2}\)O\({}_{5}\) in 0.9 BaTiO\({}_{3}\)-0.1(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramic triggered the formation of Ba\({}_{6}\)Ti\({}_{14}\)Nb\({}_{2}\)O\({}_{39}\) precipitates with increased quantity. The distributed second phase suppressed the sintered density and generated porosity in 0.9 BaTiO\({}_{3}\)-0.1(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramic. Figure 2: _Cont._  
Figure 3: Cont. Figure 2: XRD patterns of 0.9 BaTiO\({}_{3}\)–0.1(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramics with various amounts of (**a**) Ta\({}_{2}\)O\({}_{5}\) and (**b**) Nb\({}_{2}\)O\({}_{5}\) sintered at 1215 \({}^{\circ}\)C for 2 h.  
Figures 4 and 5 show the TCCs and dielectric losses _versus_ temperature, measured at a frequency of 1 kHz, of 0.9 BaTiO\({}_{3}\)-0.1(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramics with various amounts of added Ta\({}_{2}\)O\({}_{5}\) and Nb\({}_{2}\)O\({}_{5}\) sintered at 1215 \({}^{\circ}\)C, respectively. Some of the dielectric properties, including the Curie point, dielectric constant, and tan\(\delta\) value at 25 \({}^{\circ}\)C and TCCs at both 25 \({}^{\circ}\)C and 200 \({}^{\circ}\)C, are also listed in Table 2. The temperature dependence of the 0.9 BaTiO\({}_{3}\)-0.1(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramics became flattened with  
Figure 3: SEM micrographs of the sintered surfaces (**a**), (**c**), (**e**). (**g**), and (**i**) and the fractured surfaces (**b**), (**d**), (**f**), (**h**), and (**j**) of 0.9 BaTiO\({}_{3}\)–0.1 (Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramic sintered at 1215 \({}^{\circ}\)C for 2 h. (**a**) and (**b**) are pure 0.9 BaTiO\({}_{3}\)–0.1(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramic; (**c**) and (**d**) correspond to the ceramic with 1.0 mol% Ta\({}_{2}\)O\({}_{5}\); (**e**) and (**f**) correspond to the ceramic with 2.0 mol% Ta\({}_{2}\)O\({}_{5}\); (**g**) and (**h**) correspond to the ceramic with 1.0 mol% Nb\({}_{2}\)O\({}_{5}\); and (**i**) and (**j**) correspond to the ceramic with 2.0 mol% Nb\({}_{2}\)O\({}_{5}\). an increase in the dopant contents of Ta\({}_{2}\)O\({}_{5}\) and Nb\({}_{2}\)O\({}_{5}\). The TCC curves near the Curie point were dramatically suppressed, and a broad and diffuse phase transition occurred in all samples, leading to smooth dielectric temperature characteristics over a relatively broad temperature range (\(-55\) to \(200\)\({}^{\circ}\)C). The temperature corresponding to the maximum of the diffuse phase transition (\(T_{\rm{m}}\)) increased with the Ta\({}_{2}\)O\({}_{5}\) content, but there was no visible change with an increase in the Nb\({}_{2}\)O\({}_{5}\) content. For instance, \(T_{\rm{m}}\) corresponding to the \(0.9\)BaTiO\({}_{3}\)-\(0.1\)(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramics with 1.0, 1.5, and 2.0 mol\(\%\) Ta\({}_{2}\)O\({}_{5}\) content appeared to be around \(145\)\({}^{\circ}\)C, \(150\)\({}^{\circ}\)C, and \(180\)\({}^{\circ}\)C, respectively, while those with 1.0, 1.5 and 2.0 mol\(\%\) Nb\({}_{2}\)O\({}_{5}\) had a similar \(T_{\rm{m}}\) of approximately \(140\)\({}^{\circ}\)C. It is apparent that the Ta\({}_{2}\)O\({}_{5}\) content can effectively elevate the \(T_{\rm{m}}\) of the sintered ceramics. Figure 4: **(a)** TCCs and **(b)** dielectric losses _versus_ temperature of \(0.9\)BaTiO\({}_{3}\)–\(0.1\)(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) ceramics with various amounts of Ta\({}_{2}\)O\({}_{5}\) sintered at \(1215\)\({}^{\circ}\)C (measured frequency = 1 kHz; heating rate = 2 \({}^{\circ}\)C/min; applied voltage = 1 V).