Microwave sintering of dielectric CaCu3Ti4O12: An interfacial conductance and dipole relaxation effect

Crystal Growth & Design

Sharma

et al. 2015

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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.

Section: Introductionmentioning

confidence: 99%

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

Crystal Growth & Design

Sharma

et al. 2015

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“…Its colossal dielectric constant ( [10 4 ) and low tangent loss (\10 -2 ) are combined with long temperature invariance (100-500 K) [1][2][3][4]. A large number of mechanisms have been suggested to explain the origin of its colossal dielectric response [1][2][3][4][5][6][7][8][9][10]. Some group proposed that this response was based on intrinsic effects such as perfectly stoichiometric, defect-free and single-domain crystal [1,3].…”

Section: Introductionmentioning

confidence: 99%

“…Some group proposed that this response was based on intrinsic effects such as perfectly stoichiometric, defect-free and single-domain crystal [1,3]. While, other believed that this response in attributed to extrinsic effects such as defects, domain boundaries, inter barrier layer capacitance, Cu rich grain boundaries, nanoscale disorder, electrode polarization, bimodal grain distribution, Schottky type barriers at grain boundary, thermally active dielectric relaxation, and lattice distortion [4][5][6][7][8][9][10][11][12]. However, inter barrier layer capacitance (IBLC) model, which based on semiconducting grains and insulating grain boundaries, is widely accepted.…”

Section: Introductionmentioning

confidence: 99%

Structural and impedance spectroscopic studies of spark plasma sintered CaCu3Ti4O12 dielectric ceramics: an evidence of internal resistive barrier effect

J Mater Sci: Mater Electron

Senguttuvan

2016

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A giant dielectric constant CaCu 3 Ti 4 O 12 ceramic was prepared by solid-state reaction route. Powders were spark plasma sintered at 1050°C for 30 min. Rietveld refined XRD pattern reveals the formation of pure phase cubic perovskite CCTO. The dielectric properties were characterized in a broad frequency range of 10 Hz-8 MHz at temperatures 20-120°C. The grain size of sintered pellets was found in range of 12-15 lm. Impedance spectroscopic analysis shows that the observed semicircle in the Cole-Cole plot was associated with grain boundary relaxation effect. This study reveals that there is an evidence of internal resistive barrier which responsible for a giant dielectric constant in CaCu 3 Ti 4 O 12 ceramic. An Arrhenius temperature dependent relaxation effect was observed in grain boundary. Using the characteristic frequency of relaxation peak, grain boundary capacitance was calculated to be 0.27 lF. It was found that on increasing the temperature, the resistance of grain boundaries was decreased rapidly as compared to that of the grains. The activation energy of grain boundary was calculated to be 0.165 eV.

“…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].…”

Section: Introductionmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

J Mater Sci: Mater Electron

Senguttuvan

2015

Self Cite

CaCu 3 Ti 4 O 12 nanocrystals have been synthesized by the microwave flash combustion technique. The calcined powders were spark plasma sintered at 1050°C for 10 min. The surface morphology of sintered samples was studied by SEM. The effects of grain boundary activation energy on dielectric properties of CCTO were investigated by collecting the dielectric data in the frequencies of 30 Hz-8 MHz at temperatures of 20-100°C under dc bias of 0-6 V. The potential energy barrier at grain boundary has been examined by dc bias experiments. It is observed that, with an increase in dc bias from 0 to 6 V, the grain boundary activation energy decreases from 0.532 to 0.463 eV. The reduction in such grain boundary activation energy results in the decrease in dielectric constant. It is noticed that CCTO ceramic at room temperature under zero dc bias has a colossal dielectric constant of 20,000 (at 100 Hz). Using the cole-cole plot, grain and grain boundary resistance are calculated to be 13 and 52,100 X, respectively.