Study of dielectric relaxation and Polaron Conductivity Mechanism in Sodium nitroprusside (SNP): Na2[Fe(CN)5(NO)].2H20

Abstract In this study, the crystal structure of sodium nitroprusside, Na2[Fe(CN)5(NO)].2H20, has been determined by an analysis by X-ray diffraction (XRD). The crystal is orthorhombic, space group Pnnm. This compound is characterized by different techniques: X-ray diffraction (XRD), differential scanning calorimetry (DSC) and impedance spectroscopy. For electrical properties, impedance spectroscopy was performed at a frequency range of 20 Hz – 2 MHz. The dependence of AC conductivity on frequency was found to satisfy Jonscher’s universal power law at different temperatures σ ( ω ) = σ D C ( ω , T ) + A ω S ( T , ω ) . This suggested hoping conduction due to three theoretical models. The latter can be attributed to the correlated barrier hopping (CBH) model in region I, overlapping large polaron tunneling (OLPT) in region II and non-overlapping small polaron tunneling (NSPT) mechanism in region III. The temperature dependence and dielectric relaxation of the DC conductivity satisfied the Arrhenius law. The activation energy ranged from 0.033 to 0.164 eV and was similar in the conduction and relaxation mechanisms, indicating that the transport mechanisms were based on hopping phenomena. Moreover, the modulus plots has been characterized by full width at half height or in terms of a non-experiential decay function φ(t)=exp(−t/τ)β. The values of the activation energies obtained from the electrical conductivity and electric modulus are near; which suggests that the transport is probably due to the ion hopping mechanisms. Furthermore, this behavior was confirmed by both Nyquist and Argand's plots of dielectric impedance at different measuring temperatures.