Dielectric Properties of Ceramic, CaCu3Ti4O12, Substituted with Sr or Ba

There has been a considerable interest in non-ferroelectric perovskite oxide CaCu3Ti4O12 (CCTO). This material was discovered to possess one of the largest static dielectric constants, reaching nearly ε ~ 80, 000 for single-crystal samples at room temperature. This compound has centrosymmetric structure at room temperature with cubic space group Im3. Because of such incredibly high dielectric constant, the structure, dielectric and electrical properties of CaCu3Ti4O12 substituted at Ca-site with other alkaline earth metals i.e. Ba and Sr as substitution elements were studied. An extensive studies were carried out on the dielectric properties of the Ca1-xBaxCu3Ti4O12 and Ca1-xSrxCu3Ti4O12 where x = 0.5, 0.52, 0.56 and 0.6 at various temperatures. The substitutions were based on ionic radius (rCa < rSr < rBa) and the dielectric studies of Ca1-xMxCu3Ti4O12 (where M = Sr, Ba) have not been reported so far. There are two categories in the experimental investigation. First, is the X-ray diffraction that is vital to provide evidence to the proposed model of dielectric behavior. Secondly, the main experiment consists of alternating current conductivity measurement where the ability to store charge (capacitance) and conductance can be investigated. The XRD measurements reveals that the lattice parameter of CaCu3Ti4O12 after substitution of Sr2+ and Ba2+ changes while the pattern can be assigned to all the lines on the basis of a cubic symmetry. Single–phase for Ca1-xSrxCu3Ti4O12 was observed while for Ca1-xBaxCu3Ti4O12 it was found as multi-phase with some impurity element in the compound. The electrical measurement was performed using High Dielectric Resolution Analyzer, measured as a function of frequency from 10-2 Hz to 106 Hz. The data collected were plotted in log-log scale of frequency against real and imaginary of permittivity and conductivity respectively. The graphs were then fitted using the universal law to obtain the properties and mechanism that took part, with parameters involved such as m, n and p. Most of the fitted graphs showed that Ca1-xBaxCu3Ti4O12 and Ca1-xSrxCu3Ti4O12 consisted of quasi-dc, dipolar mechanism, conductance G, and some Rs effect. The substitution of Sr2+ and Ba2+ into Ca-site of CaCu3Ti4O12 reveals the specific behavior of this material when it is doped with a higher radius of the element. However, substitution of Sr2+ has apparently given the highest value of dielectric constant i.e. ~ 2.6 x 102 when substituted by 50 mole % of Sr2+ at Ca-site of CaCu3Ti4O12.

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