## 3 Results and Discussion
### Microstructural Analysis
#### 3.1.1 STEM-EDX  
The microstructure of KZM-100-MOD-Y and BT02-MOD-Y, obtained by STEM, is shown in Figures 5 and 6, respectively. Increased grain growth occurred in both samples, as a consequence of liquid sintering [15; 24]. After 1 h of sintering, KZM-100-MOD-Y had nonuniform grain size, up to around 400 nm in diameter.  
EDX analysis using the Cliff-Lorimer method showed uniform composition in KZM100-MOD-Y around the sample, based on 7 chosen points presented in Figure 5. EDX mapping of Ba, Ti, O and Y distribution has revealed that Y is highly dispersed in the BaTiO\({}_{3}\), leading to a conclusion that the used modification method with Yttrium organic salt was successful.  
BT02-MOD-Y exhibited more uniform size distribution than KZM100-MOD-Y but with a grain size up to 1 \(\upmu\)m. In both cases, grain size was around 10 times larger than for pure commercial KZM-100 and BT02. In addition, BT02-MOD-Y showed higher regularity in grain shape than KZM-100-MOD-Y, while the latter had a more densified microstructure.  
Similar to in sample KZM100-MOD-Y, a uniform composition was confirmed in BT02-MOD-Y, based on 7 chosen points presented in Figure 6. Yttrium was identified along the grain boundary in both samples, with over 2 times higher content in BT02-MOD-Y, which could lead to a higher dielectric constant value. A drop of O content indicates slight degradation of the BaTiO\({}_{3}\) phase during high temperature modification of grains.  
EDX analysis in both samples showed that Ba/Ti ratio is nonstoichiometric (Tables 1 and 2), indicating replacement of Ti\({}^{4+}\) with rare earth element.  
Formation of core-shell structure is presented in Figure 7. Shell thickness varies from 2 nm to 10 nm independent of the grain size, which leads to the conclusion that it depends on an amount of a doping element. It has been reported that the shell thickness has a small influence on dielectric constant, predominantly controlled by the grain size [12].  
Figure 5: STEM of KZM100-MOD-Y with marked points for energy dispersive X-ray analysis (EDX).  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Spectrum** & **In Stats.** & **O** & **Si** & **Ti** & **Y** & **Ba** & **Total** \\ \hline Spectrum 1 & Yes & 18.12 & 0.18 & 18.30 & 0.38 & 63.01 & 100.00 \\ Spectrum 2 & Yes & 18.17 & \(-\)0.24 & 18.36 & 0.77 & 62.96 & 100.00 \\ Spectrum 3 & Yes & 16.43 & 0.32 & 19.61 & 1.55 & 62.09 & 100.00 \\ Spectrum 4 & Yes & 16.61 & 0.28 & 17.64 & 1.21 & 64.26 & 100.00 \\ Spectrum 5 & Yes & 19.38 & 0.00 & 17.68 & 1.63 & 61.32 & 100.00 \\ Spectrum 6 & Yes & 15.80 & 0.02 & 16.92 & 1.01 & 66.26 & 100.00 \\ Spectrum 7 & Yes & 17.35 & \(-\)0.07 & 18.14 & 0.95 & 63.63 & 100.00 \\ \hline Mean & & 17.41 & 0.07 & 18.09 & 1.07 & 63.36 & 100.00 \\ \hline Std. deviation & & 1.24 & 0.20 & 0.83 & 0.44 & 1.60 & \\ Max. & & 19.38 & 0.32 & 19.61 & 1.63 & 66.26 & \\ Min. & & 15.80 & \(-\)0.24 & 16.92 & 0.38 & 61.32 & \\ \hline \hline \end{tabular}
\end{table}
Table 1: EDX analysis of different points in KZM100-MOD-Y.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Spectrum** & **In Stats.** & **O** & **Si** & **Ti** & **Y** & **Ba** & **Total** \\ \hline Spectrum 1 & Yes & 9.49 & 0.15 & 17.30 & 2.25 & 63.60 & 100.00 \\ Spectrum 2 & Yes & 10.67 & 0.11 & 17.66 & 2.02 & 63.16 & 100.00 \\ Spectrum 3 & Yes & 11.89 & 0.16 & 17.46 & 2.68 & 61.16 & 100.00 \\ Spectrum 4 & Yes & 13.29 & \(-\)0.10 & 15.76 & 2.37 &