## 3 Results and Discussion
### Microstructural Investigations  
Figures 6 and 7 show SEM micrographs of the Ba(Co\({}_{0.7}\)Zn\({}_{0.3}\))\({}_{1/3}\)Nb\({}_{2/3}\)O\({}_{3}\) (BCZN) ceramics of samples _S1_ and _S1a_, respectively. The SEM images were recorded (Figures 6a and 7a) on the surface; (Figures 6b and 7b) a fractured surface; (Figures 6c and 7c) on grain boundaries; (Figures 6d and 7d) and on longitudinally polished sections for these two cases just described. From Figure 6a it can be seen that the micrograph confirms the presence of two phases on the surface of the ceramics, needle-shaped grains and plate-shaped grains. Based on previous work, the needle-shaped grains are identified as Ba\({}_{8}\)(Co,Zn)\({}_{1}\)Nb\({}_{6}\)O\({}_{24}\), while the plate-shaped grains consist of Ba(Co\({}_{0.7}\)Zn\({}_{0.3}\))\({}_{1/3}\)Nb\({}_{2/3}\)O\({}_{3}\)[10]. This result is in agreement with the XRD data (Figure 2a). The SEM image of the fractured surface (Figure 6b) reveals that the specimens consist of a single and homogeneous phase. Figure 6c shows a micrograph highlighting a grain boundary with a typical grain size of approximately 14 microns. In addition, the large amounts of residual pores were mainly located along the grain boundaries. This porosity is observed also in the fractured surface (Figure 6b) and in longitudinally polished sections (Figure 6d). Figure 6d is a backscattered SEM image of a longitudinally polished section of a BCZN ceramic. It can be seen that the surface clearly consists of two different domains, appearing as a light grey area (marked by 1) and a dark grey area (marked by 2) on the micrograph. In order to get a better insight into the chemical composition of these phases, EDS data were collected in these two areas. The atomic percentages derived from the EDS spectra are given in Table 1. The atomic percentages of the light grey area (zone 1) are close to the theoretical values expected for Ba\({}_{8}\)(Co,Zn)\({}_{1}\)Nb\({}_{6}\)O\({}_{24}\), while the percentages of the dark grey area (zone 2) agree quite well with those of Ba(Co\({}_{0.7}\)Zn\({}_{0.3}\))\({}_{1/3}\)Nb\({}_{2/3}\)O\({}_{3}\). Those two compounds were also identified by XRD at the surface of the specimen (Figure 2a). Figure 6: SEM micrographs of BCZN ceramics (\(S1\)): (**a**) of a surface; (**b**) of a fractured surface; (**c**) of a grain boundary; and (**d**) of a longitudinally polished section. Figure 7: SEM micrographs of BCZN ceramics (\(S1a\)): (**a**) of a surface; (**b**) of a fractured surface; (**c**) of a grain boundary; and (**d**) of a longitudinally polished section. Figure 7 shows the micrographs of the post-sinter annealed BCZN sample (_S1a_). The microstructure morphology observed after the annealing step was similar to that of the sintered sample (_S1_), while significant changes are identified in terms of density and surface composition of the specimen. Figure 7c reveals a persistent secondary phase in the surface of the specimens (needle-shaped grains). These results are also in agreement with the XRD analyses (Figure 3a). It is interesting to note that the annealing step at 1300 \({}^{\circ}\)C for 30 h has no effect on the grain growth. In contrast, secondary phase formation is very marked. The EDS analysis (Figure 7d), reveals a light grey area (zone 1) and a dark grey area (zone 2) comparable to the surface of the sintered ceramic (Figure 6d) as shown in Table 1.  
Figures 8 and 9 show SEM micrographs of the BCZN ceramics after sintering and annealing steps. The SEM images were acquired under the same conditions as described above. Figure 8a-d shows the microstructures of sample _S2_. A significant change in microstructure was observed on these samples with a 0.6-2.3 \(\upmu\)m fine grained microstructure developed at this sintering temperature, with very few residual pores mainly located along grain boundaries (Figure 8c). Figure 9a-d shows the microstructures of the post-sinter annealed BCZN sample (_S2a_). No significant difference is found in the microstructure after the annealing process.