Study of the optical properties and frequency-dependent electrical modulus spectrum to the analysis of electric relaxation and conductivity effect in zinc oxide nanoparticles

In this article, the optical and dielectric properties along with electric relaxation behaviour of the zinc oxide nanoparticles (ZnO NPs) with an average size ≈ 32.5 nm were studied. The band gap, and free carrier concentration of the ZnO NPs have been found to be 3.73 eV, and ≈ 5.55 × 10¹² per cm³, respectively. Dispersion parameters and nature of dispersion have been studied from optical spectrum. X-ray diffraction investigation revealed that the crystalline phase is hexagonal with atomic fraction ≈ 75.44%. The overall behaviour of the dielectric constants of ZnO NPs has obeyed Koops model. Relaxation behaviour and defect state response inside ZnO NPs have been observed in the dielectric studies. The relaxation time varies from 8.0585 × 10^–5 to 7.8447 × 10^–5 s with temperature (T) ranges from 323 to 573 K, respectively, calculated from the electric modulus study. The AC conductivity complies the Jonscher’s universal power law and the observed hopping of electron is the correlated barrier hopping. The activation energy of the ZnO NPs is found to be ≈ 93 meV from the temperature-dependent DC conductivity analysis. The real part of complex impedance showed a negative temperature coefficient of resistance nature with increase the temperature from 473 to 673 K in the low-frequency zone. The equivalent circuit for the complex impedance analysis at T = 673 K has been studied from Cole- Cole equation and Nyquist plot. The observed properties of ZnO NPs are very important for electric storage, sensing and optical semiconductor devices.