Chandrahas Bharti

Structural and Ferroelectric Properties of Complex Perovskites Pb(1-x)Bax(Fe1/2Ta1/2)O3 (x = 0.00, 0.05, 0.1, 0.15)

We have synthesized the complex perovskite oxides Pb(1-x)Bax(Fe1/2Ta1/2)O3 (where x = 0.0, 0.05, 0.10 and 0.15) by two steps Coulombite precursor process in cubic phase and studied the effect of Ba substitution in Pb(Fe1/2Ta1/2)O3 through the dielectric and ferroelectric properties in the frequency range from 100 Hz to 1 MHz and in the temperature range from 118 to 363 K. The temperature dependence of the dielectric constant at different frequencies gives diffuse peaks which have been attributed to the occurrence of relaxor ferroelectric behaviour in Pb(1-x)Bax(Fe1/2Ta1/2)O3. The magnitudes of ϵ′m, the maximum value of dielectric constant and Tm, the temperature corresponding to ϵ′m are decreased with an increase of Ba2+ ion in the materials. There is evidence of Vogel-Fulcher type relaxational freezing in the samples. The analysis of real and imaginary parts of the dielectric permittivity with frequency has been performed assuming a distribution of relaxation times as confirmed by Cole-Cole plots.

Electrical Properties of Rare Earth Double Perovskite Sr2CeSbO6

The double perovskite oxide strontium cerium antimonate, Sr2CeSbO6 (SCS) is synthesised by solid state reaction technique. Thermal behaviour of SCS are investigated using thermogravimetric analyser and differential scanning calorimeter in the temperature range from 303 to 1500 K. Dielectric relaxation spectroscopy is used to investigate the frequency dependent dielectric relaxation in SCS in the frequency range from 100 Hz to 1 MHz and in the temperature range from 303 to 703 K. The frequency dependent electrical data are analysed by impedance formalism. The relaxation mechanism of the sample is modelled by Davidson-Cole equation (modified Debye equation). The frequencies corresponding to the maxima of imaginary part of impedance at the various temperatures are found to obey the Arrhenius law with activation energy ∼ 0.15 eV. The scaling behaviour of imaginary part of impedance suggests that the relaxation describes the same mechanism at various temperatures.

Structural and Electrical Properties of Rare Earth Double Perovskite Oxides Ba2CeMO6 (M = Ta5+ and Nb5+)

We have synthesized rare earth double perovskite oxides barium cerium niobate Ba2CeNbO6 (BCN) and barium cerium tantalate Ba2CeNbO6 (BCT) by solid state reaction technique and studied the structural and electrical properties. The x‐ray diffraction pattern at room temperature (25° C) shows monoclinic structure with the lattice parameters, a = 5.9763 A, b = 5.975 A and c = 8.48 A and β = 90.04° for BCN and a = 5.9763 A, b = 5.975 A and c = 8.48 A and β = 90.034° for BCT. Scanning electron micrograph (SEM) shows the formation of grains with different shape and size The AC electrical conductivity (σ) ( = ωeoE″) is obtained from the temperature dependence of the real (E′) and imaginary (e”) components of the complex dielectric constant E* ( = E‐−jE″). The frequency dependent conductivity spectra follow the universal power law.

Dielectric Relaxation of A2ErNbO6 (A = Ba2+ and Sr2+)

Double perovskite oxides barium erbium niobate, Ba2ErNbO6 (BEN) of cubic structure having lattice parameters a = b = c = 2.970 5 A and strontium erbium niobate, Sr2ErNbO6 (SEN) of monoclinic structure having lattice parameters, a = 6.888 A, b = 4.087 A and c = 5.059 A and β = 94.87° are synthesized by solid state reaction technique. The dielectric relaxation of BEN and SEN have been investigated using alternating current impedance spectroscopy. The frequency dependent electrical data are analyzed in the framework of impedance and modulus formalism. The Cole—Cole approach is used to explain the relaxation mechanism.