Constant Material CaCu3Ti4O12 Research Articles

Dielectric loss management by antimony (Sb) incorporation in giant dielectric CaCu3Ti4O12

The partial substitution of Sb5+ on the Ti site for giant dielectric constant material CaCu3Ti4O12 (CCTO) has been done in the present paper, and the effect of Sb substitution on the microstructural, dielectric and electrical property of the material is investigated. The main objective of this paper is to minimize high loss tangent (tan δ) which has restricted the practical applications of CCTO. XRD analysis carried out on the as-synthesized powders confirms formation of single phase material accompanied by dopant-induced lattice constant shrinkage. Scanning electron microscope images demonstrate that the grain size of sintered ceramic samples decreases with the increasing Sb content. The dielectric response of sintered CaCu3Ti4−xSbxO12 samples studied by precision LCR meter suggests that Sb doping is an effective way for maintaining a high dielectric constant and low loss over a broad range in temperature and frequency. Room temperature complex impedance spectroscopy analysis suggests that all compounds are electrically heterogeneous consisting of semiconducting grains and insulating grain boundaries establishing internal barrier layer capacitance model. These results indicate that Sb-doped CCTO ceramics have a favorable prospect to be able to stimulate practical applications.

Molten Salt Synthesis of Nanocrystalline Phase of High Dielectric Constant Material CaCu3Ti4O12

Nanocrystalline powders of giant dielectric constant material, CaCu3Ti4O12 (CCTO), have been prepared successfully by the molten salt synthesis (MSS) using KCl at 750 degrees C/10 h, which is significantly lower than the calcination temperature (approximately 1000 degrees C) that is employed to obtain phase pure CCTO in the conventional solid-state reaction route. The water washed molten salt synthesized powder, characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM) confirmed to be a phase pure CCTO associated with approximately 150 nm sized crystallites of nearly spherical shape. The decrease in the formation temperature/duration of CCTO in MSS method was attributed to an increase in the diffusion rate or a decrease in the diffusion length of reacting ions in the molten salt medium. As a consequence of liquid phase sintering, pellets of as-synthesized KCl containing CCTO powder exhibited higher sinterability and grain size than that of KCl free CCTO samples prepared by both MSS method and conventional solid-state reaction route. The grain size and the dielectric constant of KCl containing CCTO ceramics increased with increasing sintering temperature (900 degrees C-1050 degrees C). Indeed the dielectric constants of these ceramics were higher than that of KCl free CCTO samples prepared by both MSS method and those obtained via the solid-state reaction route and sintered at the same temperature. Internal barrier layer capacitance (IBLC) model was invoked to correlate the observed dielectric constant with the grain size in these samples.

The influence of the segregation of Cu-rich phase on the microstructural and impedance characteristics of CaCu3Ti4O12 ceramics

The influence of sintering conditions on the microstructural features and impedance characteristics of the giant dielectric constant material CaCu3Ti4O12 (CCTO) was investigated. The microstructure and impedance characteristics were found to be strongly dependent on the sintering conditions. Sintering of the CCTO ceramics at elevated temperatures (>1100 °C) for prolonged durations resulted in the segregation of Cu-rich phase, mostly confined to the surface, which was in concomitance with the appearance of the additional semicircle at the low frequency end in Impedance (Z*) plots. The absence of this additional semicircle in the Cu-deficient CCTO ceramics and the appearance of the same in Cu-rich CCTO ceramics that were deliberately fabricated corroborated the above observations. Also, La2/3Cu3Ti4O12 (LCTO), a low dielectric constant member of CCTO family, which consisted of small grains without the segregation of Cu-rich phase at the grain boundary, did not reveal the presence of additional semicircle in the Z*plots.

High-pressure x-ray diffraction study of the giant dielectric constant material CaCu3Ti4O12: Evidence of stiff grain surface

We measured the high-pressure x-ray diffraction of the giant dielectric constant material CaCu3Ti4O12 (CCTO) under both hydrostatic and uniaxial compressions. We found that the cubic structure of CCTO is stable up to 57GPa. Nevertheless we observed that CCTO has unusual compression behaviors under hydrostatic pressure. Specifically, the volume reduction is less than that under uniaxial compression below 25GPa, above it the volume reduction starts to approach and finally reaches the same value as that under the uniaxial compression at about 30GPa. We explained these remarkable phenomena by using the model that the samples are composed of grains that have shells stiffer than the cores.