Dielectric properties and AC conduction mechanism for 5,7-dihydroxy-6-formyl-2-methylbenzo-pyran-4-one bis-schiff base

Abstract

The dielectric properties and the electrical conductivity of the tetradentate Schiff base, derived from the condensation of 5,7 dihydroxy-6- formyl-2-methylbenzo-pyran-4-one with ethylenediamine has been studied in the temperature range 300 K< T<420 K and the frequency range 0.1–20 KHz. At T>350 K, both the dielectric constant, ε ′ , and the dielectric loss, ε ″ , showed a decrease with increasing frequency and increasing temperature. The broad loss peak anomalies observed are attributed to intrinsic lattice dipoles in the hydrogen bonded Schiff base investigated. The discontinuity observed in the DC conductivity-temperature dependence behavior is correlated with structural changes in the network. The AC conductivity measurements as function of temperature exhibit a frequency dependent, temperature dependent behavior. Protonic conduction prevails at temperatures below 350 K. Decrease in the AC conductivity above 350 K is also indicative of structural changes within the hydrogen-bonded conjugated system. The frequency dependent-conductivity of the Schiff base is found to be proportional to ω s . Analysis of the AC conductivity experimental data obtained, and the frequency exponent s with theoretical models reveals that the correlated barrier hopping (CBH) model is the appropriate mechanism for conduction in the Schiff base system. The barrier height, W m , between charged defect states is calculated and its value is in good agreement with the theory of hopping of charged carriers over a potential barrier.