# Rapid Laser Reactive Sintering Synthesis of Colossal Dielectric CCTO Ceramics
## 3 Results and Discussion
In addition, it is interesting that  
Figure 3: Field Emission Scanning Electron Microscopy (FESEM) images of CCTO prepared by rapid laser reacting sintering at laser power of 25 (**a**), 45 (**b**), 65 (**c**), and 85 W (**d**), respectively. the samples sintered at low power had lower loss with low permittivity, while the sample sintered at 85 W had slightly higher dielectric loss in the low-frequency region. The dielectric losses for CCTO sintered at 25 W, 45 W, and 65 W were less than 0.8 in the whole frequency range of 20-10\({}^{7}\) Hz, due to the contribution of micro-structural defects such as pores, valence diversity, and oxygen vacancies [24]. The dielectric loss also was sensitive to the micro-morphologies, which could be seen by comparison of the SEM images at different laser power rates. It should be noted that the sintered sample at 85 W exhibited lower dielectric loss (~0.1) in a wide frequency range of 10\({}^{3}\)-10\({}^{6}\) Hz, indicating that CCTO materials by laser sintering show more competitiveness for potential applications. Thus, it can be deduced that a compact structure composed of a number of smaller grains could aid in the improvement of overall dielectric performance. Figure 5 shows the dielectric permittivity and loss of CCTO sintered at 85 W with temperature at some fixed frequencies. The dielectric permittivity obviously increased with raised temperature and decreased with increasing frequency. However, in higher temperature regions (>250 \({}^{\circ}\)C), the dielectric behavior changed at a different frequency, presenting a flat platform of \(2.1\times 10^{4}\), \(1.8\times 10^{4}\), and \(1.6\times 10^{4}\) of dielectric permittivity at 1 kHz, 5 kHz, and 10 kHz, respectively. At 1 kHz the permittivity was 22,000 in the range of 200 \({}^{\circ}\)C-250 \({}^{\circ}\)C, which was the highest value. The decrease in dielectric permittivity at higher frequencies can be explained in terms of the interfacial space charge polarization, which is due to heterogeneous microstructures. The space charge polarization will be enhanced at higher temperature due to the increasing dc conductivity. As a result, the interfacial polarization has a rapid increase in permittivity at high temperatures and low frequencies [25]. Figure 5b shows the changes in tan \(\delta\) with temperature at fixed frequencies. It could be seen that the tan \(\delta\) demonstrated a trend of firstly increasing, then decreasing, and finally increasing with rising temperature for all given frequencies. Basically, the tan \(\delta\) was lower at higher frequency due to the increase in the conductivity with rising temperature, except for relaxation peaks. With increasing frequency, the location of the relaxation peaks shifted to the high-temperature region. The dielectric loss of CCTO-based ceramic materials was strongly temperature-dependent and the clear relaxation peaks could be due to the thermally activated relaxation. Figure 6 shows the variation of the real part of the impedance with frequencies at different temperatures for CCTO sintered at laser power rates of 25 W, 45 W, 65 W, and 85 W, respectively. The values of Z' decreased with increasing temperature below 10\({}^{5}\) Hz for all the samples, and then the Z' values almost merged at high frequency for the range of 10\({}^{5}\)-10\({}^{7}\) Hz. The different Z' values indicate the various electrical properties related the microstructures, leading to the dependence of Z' on frequencies. For the CCTO sintered at 25 W and 45 W, the Z' values diverged more than the samples sintered at higher power. Some reports attribute this dispersion at a lower frequency to  
Figure 4: Frequency dependence of dielectric permittivity and dielectric loss for CCTO ceramics. (**a**) the dielectric permittivity on dependence of frequency at room temperature in the frequency range of 20–10\({}^{7}\) Hz; (**b**) tan \(\delta\) on dependence of frequency of CCTO ceramics at room temperature in the frequency range of 20–10\({}^{7}\) Hz.