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

Lalatendu Biswal,Piyush R Das,Banarji Behera

doi:10.1007/s40145-014-0112-2

Abstract

In the present research work, frequency dependent electrical properties of tungsten bronze structured compounds Na2Pb2R2W2Ti4Nb4O30 (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 (Tc) is attributed to the cooperative response of the dipoles which is reduced above Tc. 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.

Highlights

Interest on tungsten bronze structured dielectric ceramics in polycrystalline or single crystal form has increased considerably because of their interesting properties for device applications [1,2,3,4,5,6]
The complex electric modulus formalism has been used to characterize the ionic conducting materials, because it can discriminate the electrical properties against the electrode polarization and other interfacial effects [9,20] and can be used to separate electrical active components with similar resistance but different capacitance
We have introduced constant phase element (CPE) in the equivalent circuit for the bulk response (Fig. 4)

Summary

Introduction

Interest on tungsten bronze structured dielectric ceramics in polycrystalline or single crystal form has increased considerably because of their interesting properties for device applications [1,2,3,4,5,6]. The electrical properties of ferroelectric materials are found to be mostly frequency dependent ( at high frequency), which keep them away from ideal Debye-like behavior. This frequency dependence of electrical properties is attributed to the distribution of relaxation time. We are reporting the frequency dependent electrical properties of polycrystalline ferroelectric ceramics Na2Pb2R2W2Ti4Nb4O30 (R = Nd, Sm) through modulus spectroscopy, admittance spectroscopy and AC conductivity analysis. We have tried to suggest physical interpretation to CPE from the study of the frequency dependent electrical properties of the above compounds. The materials were found to be ferroelectric in nature with transition temperature well above the room temperature (627 K for Na2Pb2Sm2W2Ti4Nb4O30 (NPSWTN) and 567 K for Na2Pb2Nd2W2Ti4Ta4O30 (NPNWTT))

Experimental

Results and discussion

Conclusions