Exploration of alternating current conduction mechanism and dielectric relaxation with Maxwell–Wagner effect in NiO–CdO–Gd₂O₃ nanocomposites

Abstract

Our present study reports on the synthesis of NiO–CdO–Gd₂O₃ nanocluster via sol–gel autocombustion route and investigation of its structural, morphological, and dielectric properties as a function of both temperature and frequency. The X-ray diffraction (XRD) pattern of the nanocomposites is refined with the structural parameters containing cubic phases of Gd₂O₃ (space group Ia-3), monteponite CdO (space group Fm-3m), and NiO (space group Fm-3m), and its grain growth is observed in the nanometer range. The Fourier transform infrared spectroscopy (FTIR) and energy-dispersive X-ray spectroscopy (EDX) spectra with elemental mappings confirmed fundamental metal oxide (M–O) stretching vibrations and elemental fingerprint with atomic and weight percentage, respectively. Outmost dielectric permittivity (${\varepsilon }_{r}^{{\prime}}$) ~ 1.7 × 10⁵ with moderate dielectric loss ~ 1012 is observed at 573 K (frequency @ 5 Hz) and its dielectric relaxation is explained by well-known Maxwell–Wagner type interfacial polarization accompanied by grain and grain boundary contribution. The frequency-dependent imaginary modulus ($M^{\prime\prime}$) spectra are fitted with modified double Kohlrausch–Williams–Watts (KWW) function for grain and grain boundary contribution and asymmetrical, suppressed ${M}^{{\prime}}\mathrm{versus}M^{\prime\prime}$ spectra recommends non-Debye type relaxation phenomena. The Cole–Cole plots of impedance ${(Z}^{{\prime}} \mathrm{versus} Z^{\prime\prime})$ divulge the contribution of grain and grain boundary explicitly and their corresponding activation energy is estimated 0.31 eV and 0.34 eV, respectively. The real conductivity (${\sigma }_{ac}^{{\prime}}$) is well fitted with double Jonscher power law including grain and grain boundary contribution and variation of their frequency exponent with temperatures helps us to interpret the conduction mechanism. A week crossover between polaron delocalization (overlapping large polaron tunneling) to localization (non-overlapping small polaron tunneling) is observed through weak quantum mechanical tunneling within our observed temperature window. Between 298 and 573 K, the electrons and their accompanying distortion within the lattice, originated due to self-trapping excess charge carrier, become delocalized and later it become localized within its neighboring atoms with high thermal treatment.

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