## 3 Results and Discussion
### Feasibility of \(Sb_{2}O_{3}\)-Doped PZT-BYS(x) Ceramics for Use in an Energy Harvester  
The calculated values of g\({}_{33}\) and \(d_{33}\times\)\(g_{33}\) as a function of \(\rm{Sb_{2}O_{3}}\) contents are illustrated in Figure 9. The data of \(g_{33}\) and \(d_{33}\times g_{33}\) for PZT-BYS(\(x\)) has also been shown in Table 3. From Figure 9, it is clear that the addition of \(\rm{Sb_{2}O_{3}}\) to the PZT-BYS(\(x\)) system significantly improved \(d_{33}\times g_{33}\). In general, \(d_{33}\) and \(\varepsilon_{33}{}^{\rm T}\) increase or decrease simultaneously depending on doping or processing conditions [24]. In the present case, it is observed that increasing behaviors of \(d_{33}\) and \(\varepsilon_{33}{}^{\rm T}/\varepsilon_{0}\) were not similar at \(x=0.1\). For a small amount of \(\rm{Sb_{2}O_{3}}\) (\(x=0.1\)), a considerable increase in \(d_{33}\) was observed, while \(\varepsilon_{33}{}^{\rm T}/\varepsilon_{0}\) decreased to its lowest value of 690. Therefore, at \(x=0.1\) moles of \(\rm{Sb_{2}O_{3}}\), the \(g_{33}\) and \(d_{33}\times g_{33}\) values reached a maximum value of \(57.4\times 10^{-3}\) Vm/N and \(20076\times 10^{-15}\) m\({}^{2}\)/N, respectively. On the other hand, the \(g_{33}\) and \(d_{33}\times g_{33}\) values decreased rapidly at \(x>0.1\) due to the considerably slower rate of increase in \(d_{33}\) and rapid increase of \(\varepsilon_{33}{}^{\rm T}/\varepsilon_{0}\).  
\begin{table}
\begin{tabular}{c c c c} \hline
**Composition** & **Sintering Tem.** (\({}^{\rm C}\)) & \(g_{33}\times\)\(10^{-3}\)**(Vm/N)** & \(d_{33}\times g_{33}\) (\(10^{-15}\) m\({}^{2}\)/N) \\ \hline PZT-BYS(0.0) & 1150 & 49.1 & 15,824 \\ PZT-BYS(0.1) & 1150 & 57.4 & 20,075 \\ PZT-BYS(0.2) & 1150 & 51.3 & 18,044 \\ PZT-BYS(0.3) & 1150 & 49.9 & 17,686 \\ PZT-BYS(0.4) & 1170 & 48.7 & 17,513 \\ PZT-BYS(0.5) & 1170 & 47.7 & 17,431 \\ PZT-BYS(0.6) & 1170 & 45.6 & 16,908 \\ \hline \end{tabular}
\end{table}
Table 3: The evaluated values of \(g_{33}\) and \(d_{33}\times g_{33}\) of PZT–BYS(\(x\)) ceramics as a function of \(\rm{Sb_{2}O_{3}}\) content at optimum sintered temperature.  
Figure 8: Temperature dependence of dielectric constant for different \(\rm{Sb_{2}O_{3}}\)-doped PZT–BYS(\(x\)) ceramics.  
A list of piezoelectric energy-harvesting parameters reported recently is provided in Table 4 for comparison with the present results. In Table 4, clearly, PZT-BYS(\(x\)) possesses a considerably higher figure of merit with a high \(g_{33}\) value in comparison to the commercially available and recently reported materials. Furthermore, most of the recent works reported a high figure of merit after doping relaxor-type materials into the PZT system. Doping relaxor-type materials into the PZT system evidently causes an abrupt decrease in the \(T_{\rm C}\), which limits the application temperature range of these materials [39; 40; 41; 42; 43]. On the other hand, Sb\({}_{2}\)O\({}_{3}\)-doped PZT-BYS(0.1) shows a high transduction coefficient without much lowering the \(T_{\rm C}\). Therefore, it might be concluded that PZT-BYS(\(x\)) with \(x\) = 0.1 moles of Sb\({}_{2}\)O\({}_{3}\) content could be considered as a good candidate material for piezoelectric energy-harvesting devices.