Response In CaCu3Ti4O12 Ceramics Research Articles

Significantly improved non-ohmic and giant dielectric response in CaCu3Ti4O12 ceramics by incorporating Portland cement

The giant dielectric and nonlinear current–voltage properties of CaCu3Ti4O12 (CCTO) incorporating Portland cement (PC) were investigated. Analysis revealed that the microstructure of the CCTO/PC ceramics was highly dense. Using the microstructure analysis and theoretical calculation, the elements in PC (i.e., Al, Si, Fe, K, Cr, and Mg) can substitute into the CCTO structure, giving rise to enhanced electrical properties of the grains and grain boundaries. As a result, the giant dielectric and nonlinear current–voltage properties of CCTO/PC were significantly improved. The low–frequency loss tangent of CCTO/PC was greatly reduced, by a factor of 10, while the dielectric permittivity of the ceramics was still large (∼104) over a frequency range of 102–106 Hz. Interestingly, the nonlinear coefficient (α) and electric field breakdown (Eb) of the CCTO/PC ceramics were greatly enhanced by factors of 2 and 30, respectively. Impedance spectroscopy analysis revealed large increases in α and Eb, as well as a decrease in the loss tangent due to a significant increase in the grain boundary resistance of CCTO/PC ceramics. Changes in giant dielectric and nonlinear electrical properties can be well described by the internal barrier layer capacitor model based on space charge polarization at the internal interfaces.

Grain size independence of giant dielectric permittivity of CaCu3Ti4−xScxO12 ceramics

The dielectric and electrical properties of CaCu3Ti4−xScxO12 (x=0, 0.04, 0.08, and 0.20) ceramics prepared by a solid-state reaction method were investigated. Grain sizes of CaCu3Ti4O12 were greatly reduced by doping with Sc3+. Surprisingly, the dielectric constant of CaCu3Ti4−xScxO12 ceramics with x=0−0.08 largely increased as the mean grain size decreased. This behavior was extremely hard to produce in CaCu3Ti4O12 ceramics. The nonlinear current−voltage properties CaCu3Ti4−xScxO12 ceramics were significantly degraded. The grain boundary (GB) resistance decreased with increasing Sc3+ concentration even though the density of GB layer increased. This resulted in enhancement of a low-frequency loss tangent due to increased dc conduction. Substitution of some Sc3+ ions into Cu sites was proposed as the cause of reduction of the potential barrier height at GBs. The possible mechanisms of giant dielectric response in CaCu3Ti4O12 ceramics are discussed.

Effects of Ta5+ doping on microstructure evolution, dielectric properties and electrical response in CaCu3Ti4O12 ceramics

Abstract The effects of Ta 5+ substitution on the microstructure, electrical response of grain boundary, and dielectric properties of CaCu 3 Ti 4 O 12 ceramics were investigated. The mean grain size decreased with increasing Ta 5+ concentration, which was ascribed to the ability of Ta 5+ doping to inhibit grain boundary mobility. This can decrease dielectric constant values. Grain boundary resistance and potential barrier height of CaCu 3 Ti 4 O 12 ceramics were reduced by doping with Ta 5+ . This results in enhancement of dc conductivity and the related loss tangent. Influence of charge compensations on microstructure and intrinsic electrical properties of grain boundaries resulting from the effects of replacing Ti 4+ with Ta 5+ are discussed. The experimental data and variation caused by the substitution of Ta 5+ can be described well by the internal barrier layer capacitor model based on space charge polarization at the grain boundaries.

Relaxation Behavior of Zr Substituted CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub> Ceramics

The dielectric properties of Zr substituted CaCu3Ti4O12ceramics have been investigated in detail. Grain size decreases with Zr content increasing. The hetero-electrical microstructures of prepared samples have been confirmed by the impedance spectra. The dielectric loss has been improved by Zr doping because of the enhancement of grain boundary resistivity. A Debye-like boundary relaxation behavior has been observed in the temperature range of 220-600K. As Zr content increases, the relaxation time increases due to the higher grain boundary concentration. This work has provided an additional proof for the origin of giant dielectric response in CaCu3Ti4O12ceramics.

Oxygen-defects-related dielectric response in CaCu3Ti4O12 ceramics

Abstract A 10 mm thickness columned CaCu3Ti4O12 ceramic was fabricated by the conventional solid-state reaction method and the dielectric properties of different parts in ceramic had been investigated. For the sample close to the surface, only one Debye-type relaxation around 107 Hz was observed at room temperature. However, for the sample close to the core, another relaxation peak was observed at about 104 Hz. The results were explained in terms of the equivalent circuit model by showing in the impedance spectroscopy. Moreover, it was introduced that the low-frequency dielectric relaxation is associated with the electrode–sample contact effect based on varying sample thickness and an annealing treatment in the nitrogen atmospheres.