Structures And Giant Dielectric Response Of Modified CaCu₃Ti₄O₁₂ And Related Ceramics

Giant dielectric constant materials show great potential in the applications for miniaturization of microelectronic devices. CaCu3Ti4O12 is one of the most typical giant dielectric materials. It indicates a giant dielectric constant which keeps temperature and frequency-independent. So far, intensive investigations have been focused on its giant dielectric characteristics. To investigate the origin of the giant dielectric response in CaCu3Ti4O12 and modify its dielectric characteristics, Nd-substituted CaCu3Ti4O12 and related ceramics were prepared and their structure, microstructure and dielectric characteristics were evaluated.First, Ca1-3x/2NdxCu3Ti4O12 (x=0,0.1,0.2) ceramics were prepared by a solid state reaction process and single-phase structures were obtained for all the compositions. Dielectric characteristics of the present ceramics were evaluated in a broad range of temperature and frequency. Two significant dielectric relaxations were observed in the low and high temperature ranges. The low temperature dielectric relaxation following Arrhenius law, should be ascribed to the more intrinsic mechanisms where the mixed-valent structures of Cu+/Cu2+ and Ti3+/Ti4+ might play important roles. Dielectric characteristics of the present ceramics were modified through modifying the mixed-valent structures by Nd-substitution.Dielectric characteristics of Ca1-3x/2NdxCu3Ti4O12 (x=0,0.1,0.2) ceramics sintered at various temperatures were also investigated. For samples with x=0.1, the processing dependence of dielectric characteristics was significant controlled. The samples with x=0.1 sintered at various temperatures maintained stable dielectric characteristics even though great changes took place in microstructures. Structure characteristics of the present ceramics were further investigated. Comparing with other compositions, TiO6 octahedron in the samples with x=0.1 tilted less. Correspondingly, Ti-O distance was the smallest. Such compact structure might be responsible for the controlled processing dependence of dielectric characteristics in such sample.SrCu3Ti4O12 ceramics were prepared by a solid state reaction process, and the SrCu3Ti4O12 major phase combined with minor amount of SrTiO3 and CuO secondary phase were observed in the present ceramics. A significant dielectric relaxation was observed at low temperature which should originate from some intrinsic mechanism. Comparing with Ca1-3x/2NdxCu3Ti4O12(x=0,0.1,0.2) ceramics, the conductivity of SrCu3Ti4O12 ceramics at room temperature was significantly decreased.