Different doping elements have been used to enhance the dielectric properties of BaTiO₃ ceramic. In this work, the effect of substitution of Ba by Bi in A site and Ti by Fe in B site on structural, dielectric and electrical properties of Ba_1-xBi_xTi_0.80Fe_0·20O₃ ceramics at (x = 0.00, 0.05, 0.10 and 0.15) was investigated by X-ray diffraction, Raman spectroscopy, Scanning Electron Microscopy (SEM), Mössbauer spectroscopy as well as dielectric measurements. The Rietveld refinement results revealed that the prepared compounds crystallize in both tetragonal (P4mm) and hexagonal (P6₃/mmc) phases for x = 0.00 and 0.05 while at x = 0.10 and 0.15, the hexagonal phase disappears and only the tetragonal phase is fitted. The Raman spectra confirmed the disappearance of hexagonal phase in benefit of tetragonal phase as the Bi³⁺ substitution increases. Based on Mössbauer analyses results, all the samples are in paramagnetic state at room temperature and the Fe is oxidized under Fe³⁺ without the presence of Fe²⁺ or Fe⁴⁺ ions. The dielectric measurements as function of temperature are studied and tree broad and relaxor phase transitions were detected: from rhombohedral to orthorhombic phase T_R-O and to tetragonal ferroelectric phase T_O-T then to cubic paraelectric phase T_m. These phase transitions were displaced to the lower temperature with increasing of Bi³⁺ substitution. The values of ε′_r increase gradually with increasing of Bi³⁺contents which confirmed the enhancement of dielectric properties of BaTi_0·80Fe_0·20O₃ by Bi substitution on Ba site. The diffuse phase transitions were described by fitting the modified Uchino relation. The Cole–Cole analyses showed that both the grain and grain boundaries resistivity values are higher for Bi³⁺ substituted samples which are responsible to the dielectric properties improvement.

In this paper, we improved the dielectric properties of CaTiO₃ by adding ilmenite (FeTiO₃). For this, we synthesized (1 – x)CaTiO₃ – xFeTiO₃ for a large composition from x = 0.0 to 1.0 by using the conventionnel solid-state method. Several characterization techniques were used to study the structural and dielectric properties of these composites. Following the X-ray diffraction results we confirmed that pure CaTiO₃ (CT) and FeTiO₃ (FT) crystalize in orthorhombic phase with Pbnm and Pmmm space groups, respectively; while for x = 0.1 to 0.9 we have succeeded to synthesize these composites with the phase mixture of two Pbnm and Pmmm orthorhombic phase, without presence of any secondary phase. The Raman spectroscopy results confirm these phases mixture (for x = 0.1 to 0.9) and the pure CT and FT bands formation. The SEM micrographs of CT sample show spherical grains while with the increase of FT content, the elongated grain shape appeared. On the other hand, the grain size is minimal at x = 0.2 and 0.5 of x content and the density is improved in these samples. The dielectric measurements of these composites were investigated as function of frequency (from 20 Hz to 2 MHz) and temperature (from room temperature to 550°C). The results confirmed the stability in dielectric permittivity of CT at this range of temperature, while with adding FT we obtained a phase transition which shifted to the lower temperature with the increase of x content. In addition, the dielectric permittivity increased with the increase of x rate and reached a colossal value for the sample at x = 0.5, which confirmed the improvement of dielectric properties of CT. The frequency dependence of dielectric permittivity showed a ferroelectric behavior for all the composites.

In this work, the influence of zinc doping on structural and dielectric properties of CaCu(3-x)ZnxTi4O12 (CCZxTO with x = 0, 2.5, 5, 7.5, 10, 12.5 and 15%) ceramics sintered at 1000 ºC for 8 h was studied. The ceramic samples were prepared by the conventional solid-state and calcined at 1050 ºC for 4 h. The X-ray diffraction (XRD) analysis of pure and Zn-doped CCTO were analyzed by using Rietveld refinement with cubic CCTO phase with no trace impurity phase. The scanning electron microscopy (SEM) investigation showed that for Zn-doped CCTO, the grains distributions were homogenous with average sizes which decreased with increasing of Zn concentration. The dielectric permittivity as function of temperature showed two dielectric anomalies (weakly and strong) and the dielectric constant value largely decreased for x = 2.5%, which is about tree magnitude smaller than the pure ceramic. Then it increased and reached a maximum at x = 10%, which is larger than the value of pure ceramic. And for x > 10%, the dielectric constant decreased for about two magnitude smaller than the ceramic at x = 10%. The cole-cole diagramm for all the samples showed existence of two semi-arcs attributed to the grains and grains boundaries. It was found that the Rg values were much smaller than the Rgb value. This give an evidance on the formation of interior barrier layer capacity (IBLC).