Calcium titanate (CaTiO3) with the general formula for perovskites, ABO3, is of technological importance, particularly with regard to dielectric properties. In this work, CaTiO3 ceramic material was prepared by the conventional solid state reaction method. The dielectric properties, impedance characteristics and modulus behavior of the CaTiO3 ceramic material sintered at 1240 °C were investigated in the frequency range of 10−2-106 Hz and temperature range of 100-250 °C. The XRD analysis of the sintered CaTiO3 shows that it is an orthorhombic structure with lattice parameters a = 5.4398 Å, b = 7.6417 Å, and c = 5.3830 Å. The FESEM micrograph shows a significant difference in grain size distribution ranging from 0.26 to 2.32 μm. The AC conductivity, σAC, is found to increase with increasing temperature within the frequency range of 10−2-106 Hz confirming the hopping of electrons to be the conduction mechanism. Due to the decreasing values of the frequency exponent s with increasing temperature, the results of the σAC are discussed using the correlated barrier height (CBH) model. For dielectric studies, the dielectric constant, ε′ is found to decrease with increasing frequency. In the whole temperature range of 100-250 °C, high and low frequency plateau are observed. Each converges at high frequency (>105 Hz) for all the temperatures. The frequency dependence of loss tangent, tan δ, decreases with rise in temperature, with the loss tangent peak shifting to higher frequency. Due to its dielectric characteristics, it is a suitable candidate for developing a variety of capacitors. For the master modulus plot, the shapes remain unchanged in the temperature range considered. The Cole-Cole plots reveal that two primary relaxation processes exist in the sample for each temperature. The Nyquist plots reveal that at temperatures below 150 °C, a linear response in the imaginary part of the impedance, Z′′, is noticed. At and above 175 °C, the linear response gradually changes to a semicircle arc. The modulus behavior indicates the presence of correlation between the motions of mobile charge carriers. The plots of Arrhenius diagram of relaxation times of loss tangent, τtanδ, and imaginary part of dielectric modulus, τM′′, obey the Arrhenius law, where the activation energies calculated from the slopes are 2.09 and 2.38 eV respectively.

The combined effects of thermal treatment and single erbium (Er3+) ion-substitution (x = 0.75) on the A-site of Bi4-xErxTi3O12 compounds were investigated by scrutinizing the crystal structure, microstructural evolution, and dielectric properties. The results are compared with those of pure Bi4Ti3O12 compounds. Upon doping, the crystal structures experienced strong octahedral distortions, resulting in phase transformation from orthorhombic to monoclinic symmetry. The doped samples became highly anisotropic with increasing sintering temperature, which are accompanied by negative thermal expansion. Following the phase transformation, plate-like grains emerged at the expense of equiaxed grains, becoming more dominant as grain growth increased with sintering temperature. The grain growth rate is comparatively slower in the doped samples, implying the inhibiting role of Er. The doped samples showed relatively small loss of ε" characterized by shorter relaxation times, which compromised the dielectric constant ε′ due to the suppression of oxygen vacancies that is closely related to the smaller grain sizes and densities. Both ε′ and ε" of pure and doped samples are grain size dependent, in which the frequency responses followed the superposition of Cole-Cole and Havriliak-Negami distribution functions that correlates with the impedance studies.

No abstract