# Rapid Laser Reactive Sintering Synthesis of Colossal Dielectric CCTO Ceramics
## 3 Results and Discussion  
Figure 2 shows XRD spectra of the CCTO ceramics by laser sintering at various laser power rates. The main phase was CCTO for almost all the samples prepared in the laser power range of 25-85 W, and the diffraction peaks identified were found to be consistent with the diffraction planes of the body-centered cubic perovskite-related structure of CCTO, in accordance with No.1532138 from crystallography open database. The major peaks in the figure were found at (211), (220), (310), (222), (321), (400), (411), (422), and (440). The crystallite size was estimated from the XRD results using [PERSON]'s formula  
\[D=\frac{0.89\lambda}{\beta\cos\theta} \tag{1}\]  
where \(\beta\) is the full width half maximum (FWHM) in radians and \(\lambda\) is the X-ray wavelength. Considering that the planes of (220), (400), (422), and (440) for the sample prepared at 85 W had higher diffraction intensity, the calculated grain sizes were 25.4, 26.2, 30.4, and 32.5 nm, respectively. The average grain size was 28.6 nm. Meanwhile, the lattice parameters were calculated according to the XRD pattern 0.7381, 0.7353, 0.7353, and 0.7329 nm from 85 W to 25 W, respectively, values close to the reported 0.7391 nm. For the CCTO sample sintered at 25 W, some secondary phases, such as rutile TiO\({}_{2}\), CuO, and CaTiO\({}_{3}\), were observed from the weak peaks in the diffraction patterns. This is attributed to the lower energy supplied by laser. Generally, the calcination temperature for CCTO by the solid-state reaction method was in the vicinity of 1000 \({}^{\circ}\)C for over 10 h, and the sintered temperature was typically near 1150 \({}^{\circ}\)C, resulting in pure CCTO ceramics. [PERSON] et al. [6] reported that calcination temperature not only affects the purity of CCTO resultant, but also changes the crystallinity and surface state,  
Figure 1: Experimental process of synthesizing calcium copper titanate (CCTO) ceramics by rapid laser reactive sintering. subsequently influencing dielectric properties. They compared two group samples prepared at different calcination temperatures and found the samples prepared at 700 \({}^{\circ}\)C showed much lower crystal quality and inferior performance than at 1000 \({}^{\circ}\)C. [PERSON] et al. [23] synthesized CCTO by the conventional solid-state reaction technique, and found that the powder calcined at 950 \({}^{\circ}\)C for 12 h was completely transformed into the CCTO phase with fewer impurities. They concluded CCTO ceramics sintered at 1090 \({}^{\circ}\)C for 15 h exhibited lower dielectric loss, and that the longer sintering time could lead to substantial improvement in permittivity. Here, focused laser beams are able to generate high energy instantaneously to catalyze the chemical solid-state reaction process. When the energy is slightly lower than the reaction required, secondary phases could be detected. However, the diffraction peaks for CaTiO\({}_{3}\), CuO, and TiO\({}_{2}\) are much weaker, and the primary phase is still CCTO. With the increase in laser power, the phases of CaTiO\({}_{3}\), TiO\({}_{2}\) disappear, but the weak peak of CuO still exists up to 85 W. This could be ascribed to the copper crucible, which is suitable as substrate in this experiment after experiencing several attempts resulting in cracked zirconia ceramics induced by heat accumulation. The reaction time of laser sintering for all the samples is 30 s; a longer sintering time would have caused more impurity phases and more structural defects in the final products. In addition, it is notable that the precursor of anatase TiO\({}_{2}\) partially transformed into rutile phase during the process of the solid-state reaction by laser sintering. This is due to the essential attributes of transformation for TiO\({}_{2}\) from anatase to rutile phase once heated to high temperatures. The microstructures of the sintered CCTO are shown in Figure 3, revealing significant changes in micro-morphologies with different laser power levels.