Giant dielectric response in microwave processed CaCu3Ti4O12 ceramics: A correlation among microstructure, dielectric and impedance properties

Abstract

Polycrystalline CaCu 3 Ti 4 O 12 (CCTO) ceramics was synthesized by microwave assisted solid-state reaction. Effect of sintering at different temperatures on the crystal structure, dielectric and impedance properties was investigated in detail. Rietveld analysis of X-ray diffraction data identified that crystal structure was a mixture of cubic CCTO and monoclinic CuO phases. Lattice parameters and amount of CuO secondary phase were also estimated as a function of sintering temperature. Microstructural investigation confirmed the existance and successive increase of the melted phase near the grain boundary region with increasing temperature of sintering. Cu-rich nature of the melted phase was further confirmed by selective area EDX spectra. Dielectric and impedance properties were studied as a function of frequency (100 Hz to 1 MHz) and temperature (room temperature to 300°C). Improvement in dielectric properties as a function of sintering temperature (1000 to 1050°C) was explained in terms of reduction in grain boundary dimension due to the successive increase in Cu-rich melted phase. However, dielectric constant started falling when sintered at 1075°C, which may be accounted in terms of segregation of large amount of CuO phase after a certain temperature and hence a non-stoichiometry of Cu in CCTO lattice. Impedance data were modelled by equivalent electrical circuits to investigate different contributions of electrically heterogeneous systems. In addition, probable relaxation mechanism has been discussed on the basis of impedance and modulus data. Activation energies were calculated from different characterizations and a non-Debye-type relaxation phenomena were observed. In this work, an attempt is made to build up a correlation among synthesis procedure, sintering temperature, dielectric, impedance and microstructural properties.

The Effect of Doping on the Electrical and Dielectric Properties of Hydroxyapatite for Medical Applications: From Powders to Thin Films

“…Broad peaks indicating dielectric anomalies were observed in all the investigated composites, shifting to higher temperatures with increasing applied frequencies. This behavior is charac-teristic of relaxor ferroelectrics and is associated with diffuse phase transition behavior [256]. It was demonstrated that the temperature dependence of ε 1 in composites is influenced by the dielectric behavior of HA, BZT-BCT, and intermediate phases present in the composite materials.…”