# Rapid Laser Reactive Sintering Synthesis of Colossal Dielectric CCTO Ceramics
## 1 Introduction  
Calcium copper titanate (CaCu\({}_{3}\)Ti\({}_{4}\)O\({}_{12}\), CCTO) has received widespread attention as an excellent electroceramic material for potential applications in capacitor, memory, sensor, microelectronic, and energy storage devices [1; 2; 3; 4; 5]. CCTO is part of the Im3 space group with a pseudo-cubic perovskite structure, and in the unit cell the lattice parameter is 7.391 A, presenting an extraordinarily high dielectric permittivity (\(\varepsilon_{r}\)) and moderate dielectric loss (tan \(\delta\)) [6]. In the year 2000, [PERSON] et al. reported colossal dielectric constants (up to 10\({}^{5}\)) of the ACu\({}_{3}\)Ti\({}_{4}\)O\({}_{12}\) type (A = Ca, Sr, Ba, La, Bi, Nd). The huge value of \(\varepsilon_{r}\) is almost independent of frequency in a broad range up to 10\({}^{6}\) Hz, showing good phase stability in the temperature range of 20-600 K. This exceptional behavior could be attributed to a polarizability mechanism related with the peculiar CCTO crystal structure [7]. A completely satisfactory explanation is not yet available for this novel dielectric performance. To date, several models have been proposed to explain the origin of the large dielectric permittivity of CCTO. Among them, the generally accepted view is that the behavior is not intrinsic, and the high \(\varepsilon_{r}\) value could be ascribed to conducting grains with insulating grain boundaries through the internal barrier layer capacitance (IBLC) mechanism [8]. The IBLC model has been generally accepted by most researchers, and it supposes that CCTO includes two parts: semiconducting grains and insulating grain boundaries. The grains work as electrodes of micro-capacitors connected in series and the grain boundariescontribute to the dielectric [9]. [PERSON] et al. [10] used impedance spectroscopy (IS) to investigate the electrical microstructure of CCTO ceramics and demonstrated that they are electrically inhomogeneous, containing semiconducting grains with insulating grain boundary regions. Furthermore, compared with traditional ceramics like barium titanate or Lead Zirconium Titanate (Piezoelectric ceramic materials) (PZT) [11; 12], CCTO demonstrates high dielectric losses and low breakdown voltage, which has been the main focus of researchers. Based on the IBLC mechanism, a great number of theoretical and experimental studies have been carried out to further improve the performance of CCTO. Various processing routes to synthesize CCTO were adopted, such as high-temperature solid-state reaction, soft-chemistry, sol-gel, co-precipitation, microwave heating, and mechanical mixing methods [13; 14; 15; 16; 17]. Solid-state reactions with the prerequisite of high temperature represent a common method for the preparation of CCTO from the powders of CaCO\({}_{3}\) or CaO, CuO, and TiO\({}_{2}\), with long reaction times [18; 19]. This method normally requires at least two steps to react in the furnace: one is calcination close to 1000 \({}^{\circ}\)C for 8-12 h, and the other is sintering at 1150 \({}^{\circ}\)C for more than 10 h, which can produce pure CCTO. Even so, the solid-state route suffers the disadvantages of inhomogeneity and complex repetitive ball milling with prolonged reaction times at higher temperatures. In contrast, the laser irradiation process only needs seconds or minutes. Conventional methods usually involve the excessive consumption of energy and are not suitable for mass production. Other soft-chemistry methods, such as sol-gel and co-precipitation, allow synthesis of CCTO at a relatively low temperature with a shorter reaction time. Although the resultant is homogeneous in stoichiometric ratio at the atomic scale, the final acquisition of pure CCTO is inseparable from the processes of calcination and sintering in furnaces at high temperatures [20; 21; 22]. Here, we adopted a rapid laser reactive sintering method to synthesize CCTO, substituting the conventional furnace.