DIELECTRIC MEASUREMENTS ON SM MODIFIED BI4TI3O12 NOVEL CERAMIC

Abstract

Three-layered novel compound namely Sm modified Bi4Ti3O12 (Sm0.37Bi3.63Ti3O12) was prepared by conventional solid state route. Dielectric measurements were made in the temperature range RT-520 o C at different frequencies. The dielectric peaks of three- layered compound were found to broad unlike the other ferroelectric compounds. This kind of diffusive behavior of the title compound is explained on the basis of modified Curie-Weiss law, and an attempt is made to understand the results. o step time = 0.15 sec. is shown in the fig 1. The lattice parameters were evaluated based on the standard (parent) compound. The details were summarized in table 1. Dielectric measurements were obtained by using the HP 4192 A analyzer at different frequencies, with two terminal texture. Before obtaining the data, samples were coated with silver past on both sides of the pellets and annelid at 550 o C for 30 minutes. 3. RESULTS AND DISCUSSION The variation dielectric constant with temperature at different frequencies is shown in the fig 2. From the plots, it is observed that the peaks are found to shift towards lower temperature with increasing frequency. This behavior shows a deviation from normal ferroelectric behavior. To correlate the transition temperatures, the variation of dielectric loss against temperatures is shown in fig 3. Some class of ferroelectric materials show absence of dielectric peaks and may observe in strong dispersion in the dielectric loss response functions. The substitution of Sm for Bi may cause depressive stressing the perovskite unit cell, as a result leading to the distortion in the structure. The increase in Curie temperature of SBT, compared to BLT is attributed to the increase the structural distortion. Due to the different ionic radii of Sm &Bi and a tilt in TiO6 octahedra buckle causes an increase in the transition temperature value. The overlap population defined by Withers et al reported that the displacement of the Sm-Ti-O perovskite blocks with regards the Bi2O2 layers might contribute large polarization (ferroelectric properties) in the materials. In other words, the displacement of Sm ions in the ab-plane is dominant rather than the displacement of the Bi ions in ab-plane. However the overlap population of Ti-O in the present compound clusters is related to the displacement of Ti ions in the ab- plane. Therefore, the difference in the transition temperature is mainly due to the displacement of Ti ion in the TiO6 octahedra rather than the differences in the ionic charges of all ions.