Origin of the high dielectric constant in Sm2/3Cu3Ti4O12 ceramics

Abstract

The microstructure, crystalline structure, dielectric and electrical properties of polycrystalline Sm2/3Cu3Ti4O12 ceramics, prepared via conventional solid-state reaction were investigated. The structural evolution of these powders was analyzed by X-ray diffraction (XRD). Crystal structure investigated by Rietveld refinement was found to be cubic with space group Im3. It has been found that Sm2/3Cu3Ti4O12 ceramic shows giant dielectric permittivity values with low frequency (1 kHz) larger than 30,000 at room temperature. In the temperature domain, a new dielectric relaxation was clearly observed beyond 200 K, in addition to the well-investigated dielectric relaxation close to 100 K. This Maxwell–Wagner type of relaxation was found to be originating from the formation of external depletion layers at the electrode-sample interface. The dielectric relaxation at high frequencies in the dielectric dispersion spectra of Sm2/3Cu3Ti4O12 ceramics is caused by an IBLC effect associated with the insulating grain boundaries and the other one at low frequencies originates from an electrode polarisation effect. The activation energy of semi conducting grain is found to be similar to that of CCTO (∼0.06 eV). The observed giant value of the dielectric constant in the Sm2/3Cu3Ti4O12 ceramics originates due to polarisation at the electrode- sample interface and at the insulating grain boundary interface. The results suggest that the IBLC effect mechanism that was formerly proposed for CCTO ceramics is also valid in explaining the high dielectric constant in the compositionally and structurally CCTO-like, Sm2/3Cu3Ti4O12 ceramics.