Investigation of Relaxation Processes over Static Permittivity-Frequency Regime and the Observance of Stokes–Einstein-Debye Relation in the Plastic Crystalline Phase of Neopentylglycol

Impedance spectroscopy has been used to investigate the relaxation processes over the static permittivity (ε_s) frequency regime in the plastic crystalline phase (PC) of neopentylglycol (NPG) at the temperature range (313.3–353.6 K) and frequency from 20 Hz to 1 MHz. The data have been critically analyzed in the form of complex dielectric function (ε*), ac conductance (σ*), electric modulus (M*), and impedance (Z*) of NPG spectra. The presence of the phenomena of electrode polarization and ionic conduction was explored based on a comparative analysis of the spectra of all the complex quantities. The T-dependence of various physical quantities such as static permittivity (ε_s), Kirkwood correlation factor (g_k), dc conductivity (σ_dc), time constant due to ionic conductivity relaxation (τ_σ), electrode polarization (τ_ep), and the activation energies have been determined using well-known Arrhenius law. It was found that on a log–log scale, the dependence of dc conductivity (σ_dc) on the structural relaxation time (τ_α) of pure NPG shows a linear behavior with a negative slope of unity; hence, it fulfills the Stokes–Einstein–Debye relation quite well. This suggests that temperature has no effect on the size of the molecular environment in which ions’ movement takes place.