## 3 Results and Discussion
### Microwave Dielectric Properties  
The microwave dielectric properties of the Ba(Co\({}_{0.7}\)Zn\({}_{0.3}\))\({}_{1/3}\)Nb\({}_{2/3}\)O\({}_{3}\) ceramics were investigated for specimens _S1_, _S2_, _S1a_ and _S2a_. The measurements were recorded from polished and unpolished samples. No significant differences in dielectric properties were observed before and after polishing. This is due to their good microwave dielectric properties [9]. This observation suggests that the secondary phases of Ba\({}_{8}\)(Co,Zn)\({}_{1}\)Nb\({}_{6}\)O\({}_{24}\) and of Ba\({}_{5}\)Nb\({}_{4}\)O\({}_{15}\) seem to have no effect on the dielectric properties. The results of the dielectric measurements at about 6 GHz are gathered in Table 2.  
As displayed in Table 2, the sintering and annealing steps seem to have little effect on the dielectric constant \(\varepsilon r\) and on the temperature coefficient of the resonant frequency \(\tau_{f}\), whereas the  
Figure 8: SEM micrographs of BCZN ceramics (_S2_): (**a**) of a surface; (**b**) of a fractured surface; (**c**) of a grain boundary; and (**d**) of a longitudinally polished section.  
Figure 9: SEM micrographs of BCZN ceramics (_S2a_): (**a**) of a surface; (**b**) of a fractured surface; (**c**) of a grain boundary; and (**d**) of a longitudinally polished section.  
quality factor \(Q_{f}\) at 6 GHz is significantly affected. Thus, a high quality factor \(Q_{f}\) of 96,132 GHz, a high dielectric constant \(\varepsilon\tau\) of 34.5 and a temperature coefficient of the resonant frequency \(\tau_{f}\) of 0 ppm/\({}^{\circ}\)C were obtained for sample _S2_ (Table 2). The relative density of this specimen (_S2_) is about 6.29 indicating a high density of the obtained ceramic materials. On the other hand, a similar quality factor \(Q_{f}\) of 99,700 GHz is obtained for the annealed sample _S2a_ (Table 2) with a relative density of 6.55. In the case of specimen _S1_ (Table 2), a \(Q_{f}\) value of 36,953 GHz is observed with a relative density of 6.44. The latter value of \(Q_{f}\) is much lower than that obtained for specimen _S2_. However, the \(Q_{f}\) value of the ceramics were remarkably improved by the annealing process at 1300 \({}^{\circ}\)C for 30 h and the maximum \(Q_{f}\) value of BCZN sample (_S1a_) was 123,700 GHz, which is 25% higher than that of BCZN sample (_S1_) (Table 2). The relative density of the latter specimen is 6.56 (-96% of the theoretical density). The results in Table 2 show that high densities were obtained for all ceramics materials regardless of the processing conditions. This confirms that, from certain density values on (\(>\)90%), the \(Q_{f}\) value is independent of the density in agreement with previous data [13]. Indeed, during the sintering step, the improved \(Q_{f}\) value could be linked to differences in the ceramic microstructure as shown in Table 2, with a high \(Q_{f}\) value of 96132 was obtained for the BCZN specimen (_S2_), with a grain size of 0.6-2.3 microns. During the annealing process, the quality factor \(Q_{f}\) of the BCZN ceramics was significantly improved. It can be seen from Table 2, that the high values of \(Q_{f}\) of 99,700 and 123,700 GHz are observed of the annealed samples _S2a_ and _S1a_, respectively. This improvement of the \(Q_{f}\)-value is explained by 1:2 cation ordering in accordance with the XRD data recorded on the surface of the post-sinter annealed ceramics (_S1a_ and _S2a_), as shown in the small insert figure in Figures 3b and 5b, respectively. A similar result was previously reported which shows the increase of the \(Q_{f}\) values as a consequence of cation ordering [9]. This \(Q_{f}\) value of 123,700 GHz is higher than those obtained for the undoped and Al\({}_{2}\)O\({}_{3}\)-doped BCZN ceramics (\(Q_{f}\) = 115,307 and 61,056 GHz, respectively), published recently [14; 15], indicating that the Ba(Co\({}_{0.7}\)Zn\({}_{0.3}\))\({}_{1/3}\)Nb\({}_{2/3}\)O\({}_{3}\) materials are promising candidates for microwave device applications.