Growth of Nanocrystalline CaCu₃Ti₄O₁₂ Ceramic by the Microwave Flash Combustion Method: Structural and Impedance Spectroscopic Studies

Abstract

Nanocrystalline CaCu 3 Ti 4 O 12 ceramic powders of particle size ranging from 50 to 70 nm have been grown for the first time by the microwave flash combustion method. The structural and compositional properties of powders and sintered pellets are analyzed by X-ray diffraction, high-resolution transmission electon microscopy, scanning electron microscopy, and energy dispersive Xray spectroscopy. The dielectric properties are measured in the frequency range of 10 Hz to 8 MHz at temperatures 20−140 °C. Impedance spectroscopic studies reveal that the resistance of the grain and the grain boundary are 40 Ω and 8 MΩ, respectively. It is further observed that on increasing the measurement temperature, the decrease in the grain boundary resistance is relatively higher as compared to grain resistance. Simultaneously, the value tan δ at low frequencies (<2 kHz) increases exponentially with an increase in measurement temperatures (>80 °C). These losses are attributed to the thermally activated grain boundary electrical conduction due to copper segregation at the grain boundary. The activation energy for charge conduction is calculated to be 0.776 eV.

Dielectric properties of microwave flash combustion derived and spark plasma sintered CaCu3Ti4O12 ceramic: role of reduction in grain boundary activation energy

“…XRD and TEM measurements of CCTO nanoparticles synthesized by microwave flash combustion technique are in accordance with the our previous work [5]. In the previous work, we have demostrated that XRD patterns of CCTO synthesized by microwave flash combustion technique are match well with a body-centered cubic perovskite-like CCTO structure of cell parameter of 7.38 Å (JCPDF file no.…”

“…The detail about this synthesis was described in our previous report [5]. Briefly, aqueous solution containing Ca(NO 3 ) 2 Á4H 2 O, Cu (NO 3 ) 2 Á 4H 2 O and TiO(NO 3 ) 2 as oxidizers and CH 4 N 2 O (urea) as a fuel was irradiated with microwave power (2.45 GHz and 1.1 kW).…”

“…The tilted TiO 6 octahedron arises due to the share of different size of cations (Ca ?2 and Cu ?2 ) at A site and the bound of Cu ?2 ions to four oxygen atoms in square planar environment [1][2][3][4][5][6][7][8].…”

“…Some researchers suggested that the anomalous dielectric behaviour of CCTO is based on intrinsic effects (perfectly stoichiometric, defect-free and single-domain) [1,3], while other have attributed to extrinsic effects (defects, domain boundaries, Cu rich grain boundaries, nanoscale disorder, electrode polarization, bimodal grain distribution, Schottky-type barriers at grain boundary, thermally active dielectric relaxation, lattice distortion, and inter barrier layer capacitance) [4][5][6][7][8][9][10][11][12]. However, an extrinsic effect: inter barrier layer capacitance which based on semiconducting grains and insulating grain boundary is widely accepted.…”

“…[25], Tisubstituted Zn ferrite [26] and others have been synthesized. Recently, we have synthesized nanocrystalline CaCu 3 Ti 4 O 12 ceramic for the first time by the microwave flash combustion method [5].…”