Investigation of the Optical, Voltage and Frequency Dependent Dielectric Properties and Conductivity Effect in Copper Oxide Nanoparticles

Ben Nasr F, Guermazi H, Leroy G, Duponchel B and Guermazi S

Published on: 2022-09-20


The optical and dielectric properties along with electric relaxation of the copper oxide nanoparticles (CuO:NPs) are studied. The band gap and free carrier's concentration to effective mass ratio of the CuO are found to be 2.12 eV, and 1.57.1049 g-1 cm-3, respectively.

The structure is investigated by means of X-ray diffraction (XRD) and MEB spectroscopy. Imaginary parts of dielectric constant, volume energy loss (VELF), surface energy loss (SELF), and optical conductivity, are studied against photon energy. Optical conductivity and energy loss functions increase with photon energy, attributed to the excitation of charge carriers by the photon energy. Dielectric study was carried out at room temperature and at different bias voltages. The behavior of the dissipation factor against frequency is in accordance with Maxwell Wagner model. The increase of dielectric losses at low frequency domain proves the contribution of the grain boundaries in conduction mechanism, in accordance with the high interface state density. Moreover, the AC conductivity of CuO obeys the Jonscher’s universal power law, and the conduction mechanism is the correlated barrier hopping.


CuO nanoparticles; Dielectric properties; AC conductivity; Optical properties


The copper oxide (CuO) is an important p-type semiconductor. Its properties confer on it an advancing position in various applications[1], including catalysts[2], gas sensors[3], anti- bacterial applications[4]. Additionally, it exhibits a narrow band gap energy (1,8–2,5eV)[5]. CuO has been reported as suitable candidate for solar energy conversion materials [6]. Besides, it has a high optical transmittance in the visible energy domain and high electrical conductivity [7].

In this paper, CuO nanostructures are synthesized using a hydrothermal technique. The structural, morphological and optical properties of the synthesized powder are investigated using (XRD), Scanning electron microscopy (SEM), and UV–Vis spectroscopy. Additionally, the dielectric properties are studied as a function of applied DC-voltage and frequency. Optical and electrical parameters are computed using various theoretical models.

Synthesis of Material

The CuO powder was synthesized by the hydrothermal route. The raw materials: (CuSO4.5H2O), NaOH, hexamethylenetetramine (HTMA) and distilled water, as solvent. Further information on growth process conditions were detailed elsewhere [8].


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Results and Discussion

Structural Characterization

The XRD pattern was performed and the results are shown in Figure 1. All the obtained peaks in the pattern are well matched with the monoclinic phase of CuO crystals, and well consistent with the JCPDS card (card no.05–2529).

Figure 1: XRD patterns of CuO nanostructures.

Optical Properties

Figure 2 shows the absorbance, transmittance and reflectance spectra of CuO NPs. At short wavelengths in the near UV range, absorption is dominated by band-to-band transitions. This shows that this compound can be used as optical filters in the UV range. In the visible range, the incident light is reflected by the material. This phenomenon can be described by the classical theory of free electrons of Drude [9]. In the near infrared range, we show that the transmission is around 90%, this gives transparency in the near infrared, properties recommended for applications as transparent electrodes.

Figure 2: Absorption, transmission and reflection spectra of CuO NPs.










Figure 3: The variation of (αE)2vs. photon energy E.

The optical band gap is a major factor in such fields of science as diodes, solar cells photovoltaic’s, lasers and photoluminescence [14].

The extinction coefficient (k) is calculated from the following 

From Figure 4, (a) increases with wavelength’s increase in the UV region decreases in the visible range, and then remains substantially constant in near infrared range. The decrease of (a) can originate from various parameters such as internal electric fields within the crystal, inelastic scattering of charge carriers by phonons, or lattice deformation due to strain caused by imperfection[15].

Figure 4: Variation of (a) and (k) of the sample vs. wavelength.

The extinction coefficient (k) exhibits two absorption peaks in the UV, visible regions. Besides, Figure 4 shows a considerable decrease of the optical losses in the visible range.

Figure 5: The variation of Log (a) versus (E) for CuO NPs.