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Lanthanum and vanadium modified polycrystalline material of La0.75Bi3.25Ti2.9625V0.03O12(BLVT) of Aurivillius family, was prepared by conventional solid-state reaction method. X-ray diffraction showed single phase with orthorhombic structure. Electron microcopy was done on as-sintered and oxygen-annealed samples. Impedance studies of BLVT showed multiple impedance relaxations. Based on the impedance factor (related to full width at half maximum) and master plots, the relaxations are found to be collectively competitive. A broad dielectric peak and Curie-Weiss diffused parameter indicates diffused phase transition. Complex impedance analysis along with the log-log spectroscopic plots was studied on BLVT at 500°C. But complex impedance plot of BLVT showed single broad semicircle, unlike La0.75Bi3.25Ti3O12(BLT), which showed three semicircles on separately coated silver- and platinum- ceramic disks. However, complex modulus plot (complimentary to impedance) of BLVT showed three semicircles, which clearly indicates the tendency of formation of space charges, which might result in the accumulation of defects at electrode-ferroelectric interfaces, and considered to be a characteristic feature of the sample. In view of this, some of the BLVT samples were annealed in oxygen- and vacuum. Detailed ac-conductivity analysis suggests that double oxygen vacancies play vital role in conduction phenomenon. [ABSTRACT FROM AUTHOR]

Tri (Dy3 +) and pentavalent (Nb+5) modified new polycrystalline material of Aurivillius family (Dy0.75Bi3.25Ti2.9625Nb0.03O12) was prepared by solid-state reaction method and the lattice parameters were calculated by using X-ray diffractogram. Impedance measurements were carried out from room temperature to 500°C in the frequency range of 100 Hz to 1 M Hz. Impedance spectroscopic plots show non-Debye type and detailed ac-conductivity analysis was also employed to understand the heterogeneity of the present electro-ceramics. The results were corroborated with the proposed defect formula and in addition, thermal stimulated current measurements show that the present sample has an excellent pyroelectric response. [ABSTRACT FROM AUTHOR]

AC-impedance spectroscopic studies are carried out on lead magnesium niobate (PMN) and La-modified PMN-PT (lead magnesium niobate-lead titanate), Pb 1 - x La x [(Mg 1 + x / 3 Nb 2 - x / 3 ) 0.65 Ti 0.35( 1 - x / 4 ) ]O 3 , ceramic, with x = 0 to 0.07. Complex modulus and impedance plots exhibit two depressed semicircles and one depressed semicircle, respectively for PMN. This is attributed to the nearly same capacitance of grain and grain boundaries and higher grain boundary resistance than the grain resistance for PMN. Un-doped MPB composition of PMN-PT (0/65/35) and La-doped PMN-PT composition (7/65/35) also show similar complex modulus and impedance plots of PMN but in these samples the grain boundary capacitance was found to be higher than the grain capacitance. Cole-Cole plot shows two depressed semicircles, exhibiting grain and grain-boundary contributions in all the samples. La substitution is found to result in a broad peak in the frequency dependence of the imaginary part of the impedance and the modulus, for the temperature range 300–600°C. The maxima in the impedance and the modulus are found to shift towards higher frequencies with increasing temperature for all La-doped PMN-PT compositions, indicating a deviation from Debye behaviour. La-substitution results in broadening of the ε( T ) peak, and a marked frequency dependence of ε max (T max ), similar to that observed in PMN. It is believed that La-substitution induces the relaxor-like permittivity characteristics in MPB composition of PMN-PT by constructing higher-resistive and lower-capacitive grains, and grain boundaries. [ABSTRACT FROM AUTHOR]