Frequency dependent electrical properties of Na2Pb2R2W2Ti4Nb4O30 (R = Nd, Sm) ceramics

Abstract

Abstract:In the present research work, frequency dependent electrical properties of tungsten bronze structured compounds Na 2 Pb 2 R 2 W 2 Ti 4 Nb 4 O 30 (R = Nd, Sm) are reported. X-ray diffraction (XRD) study of polycrystalline ceramic samples confirms the formation of compounds with orthorhombic structure. Analysis of frequency dependent electrical data in the framework of modulus and conductivity formalism suggests the presence of thermally activated relaxation process in the compounds, which show Arrhenius behavior. The magnitudes of activation energies give the nature of the relaxing species. The real and imaginary parts of complex modulus trace the depressed semicircle in complex plane, suggesting non-Debye type relaxation process in the materials. The power law behavior of admittance data is successfully modeled by introducing constant phase element (CPE) to the equivalent circuit. A large value of power law parameter (n) of CPE below ferroelectric transition temperature (T c ) is attributed to the cooperative response of the dipoles which is reduced above T c . This behavior is correlated with the frequency dependence of CPE, suggesting a physical meaning to it. The frequency dependent AC conductivity at different temperatures follows Jonscher's universal power law. Almond and West formalism is used to estimate the hopping rate, activation enthalpy and charge carrier concentration in the materials.

Optical constants of CuO and ZnO particles in the terahertz frequency range

“…(9) where σ 0 is the zero-frequency electrical conductivity, and the pre-factor A (not electric-field amplitude here) and exponent n (not refractive index here) depend on the material and temperature. The value of n is smaller than unity when the conductivity is dominated by the long-range movement of charge carriers; meanwhile it is larger than 1 when short-range hopping dominates transport [53][54][55][56]. We observe a clear power-law dependence of the conductivity with  and that Jonscher's model fits well with the experimental data.…”