## 3 Results and Discussion  
PLZT compositions are generally sintered at the temperature range of 1250-1350 \({}^{\circ}\)C. In the perovskite-based composition, CuO, NiO, Li\({}_{2}\)O\({}_{3}\), and ZnO are typically the additives that use a low melting point material to lower the sintering temperature [14; 15; 16]. Among them, ZnO and NiO were selected, and the effect of these additives on low-temperature sintering of the PLZT composition was investigated. Figure 1 shows the bulk density according to the sintering temperature of PLZT when 2.0 and 2.5 wt% of ZnO and NiO are added, respectively. As the contents of the additive increased, the sintering density increased at the same temperature. It was thought that the sintering temperature was reduced by ZnO and NiO due to their low melting point during sintering. [PERSON] [17] et al. reported that when ZnO is used as a low-temperature sintering additive in the PZT composition, the sintering temperature is lowered by the formation of a liquid phase. However, in this experiment, a relatively low density was obtained at 950 \({}^{\circ}\)C even when ZnO and NiO were added up to 2.5 wt%. PbO in the PZT dielectric materials has a high volatility of over 880 \({}^{\circ}\)C. The volatilization of PbO affects the sintering density by forming a vacancy at the A-site. It was reported that the sintering properties improved as the added PbO re-compensated for the vacancy generated after volatilization when a small amount of PbO was added. [PERSON] [18] et al. confirmed the effect of low-temperature sintering on PZT ceramics by adding a small amount of PbO together with a low-melting additive. Figure 2 confirms the densification behavior after sintering at 950 \({}^{\circ}\)C when a small amount of PbO was added simultaneously to ZnO at a fixed amount of 2.5%, the amount that effectively increases the density (Figure 1). As the content of PbO gradually increased, the sintered density was improved. As mentioned above, this is assumed to be the effect of the volatilization compensation of  
Figure 1: Changes in bulk density of (Pb\({}_{0,88}\), La\({}_{0.12}\))(Zr\({}_{0.86}\), T\({}_{0.14}\))O\({}_{3}\) according to the addition of NiO and ZnO. Figure 2: Densities and shrinkages of sintered bodies at 950 \({}^{\circ}\)C according to the addition of PbO in the PLZT + ZnO (2.5 wt%) composition. PbO and liquefaction of ZnO. When more than 6 wt% of PbO was added, a density of 7.8 g\(\cdot\)cm\({}^{-3}\) and a shrinkage rate of 15% was obtained. As a result, when ZnO and PbO were simultaneously added to the PLZT composition, the densification of PLZT was completely formed at 950 \({}^{\circ}\)C.  
Based on the results in Figures 1 and 2, a composition containing 2.5 wt% of ZnO and 8.0 wt% of PbO was selected, and the change in sintering density at 950 \({}^{\circ}\)C was observed according to the amount of Sn\({}^{4+}\) substitution for Zr\({}^{4+}\). In general, when an additive is substituted, it is replaced with an ionic site with a similar ionic radius. The ionic radius of Sn\({}^{4+}\) is about 0.071 nm, and the ionic radius of Zr\({}^{4+}\) is about 0.079 nm, so it is assumed that the ionic radius of Sn\({}^{4+}\) is similar to that of Zr\({}^{4+}\)[19]. The overall change in the amount of Sn\({}^{4+}\) substitution had no significant effect on the sintering density at 950 \({}^{\circ}\)C. However, the density was slightly decreased when over 0.6 mol ratio of Sn\({}^{4+}\) was substituted. Figure 3 shows the microstructures of the body sintered at 950 \({}^{\circ}\)C according to the substitution of Sn\({}^{4+}\). A microstructure with a uniform grain size was observed as a whole. As the amount of Sn\({}^{4+}\) substitution gradually increased, the grain size decreased. The grains in which Sn\({}^{4+}\) were not substituted were larger than about 4 \(\upmu\)m but decreased to about 1 \(\upmu\)m when the Sn\({}^{4+}\) were substituted by 0.6. [PERSON] [19] et al.