## 3 Results and Discussion
### Effects of Pre-Synthesized BYS(\(x\)) Content on the Densities of PZT-BYS(\(x\)) Ceramics  
Figure 3 shows the density of PZT-BYS(\(x\)) ceramics sintered at various temperatures as a function of Sb\({}_{2}\)O\({}_{3}\) content. It is well known that electrical properties are directly related to density. Therefore, a detailed experiment was conducted to find out the optimum sintering temperature at which these ceramics reached their maximum density. From Figure 3, it is clear that the ceramics are well sintered to high densities between 1150 and 1170 \({}^{\circ}\)C. At \(x\) = 0.1-0.3, PZT-BYS(\(x\)) ceramics showed the highest density at about 1150 \({}^{\circ}\)C. At \(x\) = 0.4-0.6, the density reached its maximum at 1170 \({}^{\circ}\)C. As the piezoelectric and dielectric properties are closely related to the microstructure, and sintered density, a detailed investigation of crystal structure, microstructure, piezoelectric/dielectric and ferroelectric properties of PZT-BYS(\(x\)) ceramics sintered at their optimum temperature will be considered and discussed in the next sections. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \multirow{2}{*}{**Doping**} & **Sintering** & **Sintering** & **Grain Size** & **Density** & \(d_{33}\) & \(\varepsilon_{33}\)T & \(k_{p}\) & \(g_{33}\times 10^{-3}\) & \(d_{33}\times g_{33}\) \\  & **Tem. (\({}^{\circ}\)C)** & **Condition** & **(\(\upmu\)m)** & **(g/cc)** & **(pC/N)** & **(\(\upmu\)s)** & **(\(\upmu\)s)** & **(\(\upmu\)m)** & **(\(\upmu\)s)** \\ \hline Sb\({}_{2}\)O\({}_{5}\) & & air & 2.4 & 7.94 & 346 & 753 & 65.1 & 51.9 & 17,971 \\ Sb\({}_{2}\)O\({}_{3}\) & 1170 & air & 1.4 & 7.88 & 335 & 793 & 63.6 & 47.7 & 15,987 \\ Sb\({}_{2}\)O\({}_{3}\) & & oxygen & 2.3 & 7.96 & 350 & 738 & 64.8 & 53.3 & 18,519 \\ \hline \end{tabular}
\end{table} 
Table 1: The piezoelectric, dielectric and energy-harvesting parameters of Sb\({}_{2}\)O\({}_{3}\) and Sb\({}_{2}\)O\({}_{5}\)-doped PZT-BYS(0.1) ceramics sintered in air and in an O\({}_{2}\)-rich atmosphere. PZT-BYS: 0.99 Pb(Zr\({}_{0.53}\)Ti\({}_{0.47}\))O\({}_{3}\)–0.01 Bi[Y\({}_{(1-x)}\)Sb\({}_{x}\)]O\({}_{3}\). Figure 3: Density of PZT-BYS(\(x\)) ceramics sintered in an O\({}_{2}\)-rich atmosphere at different temperatures. Effects of Pre-Synthesized BYS(x) on the Crystal Structure and Microstructure of PZT-BYS(x) Ceramics  
The XRD patterns of PZT-BYS(\(x\)) ceramics sintered at their optimum temperatures are shown in Figure 4a. In these patterns, no detectable traces of the pyrochlore or other impurities were observed. Additionally, asymmetry and/or peak splitting in 111 and 200 reflections indicate all of the compositions are exhibiting rhombohedral-tetragonal phase coexistence [14; 15; 17]. Quantitative analysis of possible change in relative phase fraction as a function of BYS is not within the scope of this work. Nevertheless, the enlarged XRD patterns in Figure 4b indicated that the decrease in 002 reflection with an increasing amount of Sb\({}_{2}\)O\({}_{3}\) is possibly related to the decrease in volume fraction of the long c-axis of the tetragonal unit cell. Figure 5 shows the microstructures of the fracture surface containing various amounts of Sb\({}_{2}\)O\({}_{3}\) content sintered at an optimum temperature at which maximum density was obtained. A significant change in grain size was observed with the addition of Sb\({}_{2}\)O\({}_{3}\). The microstructures of the sintered samples are uniform, dense and consistent with the measured density. In the previous work, it was reported that the addition of a small amount of BY abruptly decreases the grain size of PZT due to the pinning effect of the second phase [13]. In the present case, the addition of Sb\({}_{2}\)O\({}_{3}\) doping on PZT-BYS(\(x\)) shows a further decrease in grain size. The average grain size of specimens is decreased with the increasing amount of Sb\({}_{2}\)O\({}_{3}\).