We report here structural, electrical and dielectric properties of ZnO varistors prepared with two different particle sizes for initial starting oxides materials (5 µm and 200 nm). It is found that the particle size of ZnO does not influence the hexagonal wurtzite structure of ZnO, while the lattice parameters, crystalline diameter, grain size and Zn-O bond length are affected. The nonlinear coefficient, breakdown field and barrier height are decreased from 18.6, 1580 V/cm and 1.153 eV for ZnO micro to 410 V/cm, 7.26 and 0.692 eV for ZnO nano. While, residual voltage and electrical conductivity of upturn region are increased from 2.08 and 2.38x10-5 (Ω.cm)-1 to 4.55 and 3.03x10-5 (Ω.cm)-1. The electrical conductivity increases by increasing temperature for both varistors, and it is higher for ZnO nano than that of ZnO micro. The character of electrical conductivity against temperature is divided into three different regions over the temperature intervals as follows; (300 K ≤ T ≤ 420 K), (420 K ≤ T ≤ 580 K) and (580 K ≤ T ≤ 620 K), respectively. The activation energy is increased in the first region from 0.141 eV for ZnO micro to 0.183 eV for ZnO nano and it is kept nearly constant in the other two regions. On the other hand, the average conductivity deduced through dielectric measurements is increased from 2.54x10-7 (Ω.cm)-1 for ZnO micro to 49x10-7 (Ω.cm)-1. Similar behavior is obtained for the conductivities of grains and grain boundaries. The dielectric constant decreases as the frequency increases for both varistors, and it is higher for ZnO nano than that of ZnO micro. These results are discussed in terms of free excited energy and strength of link between grains of these varistors.
This paper reports the optical properties of prepared samarium oxide Sm2O3 thin films nanoparticles using RF sputtering technique. X-ray diffraction is used to examine and characterize the prepared films. Optical measurements are carried out by employing U-V-Visible spectroscopy to study optoelectronic properties of Sm2O3 thin films. These films are highly transparent in the visible range. The average value of the optical gap belonging to the thin films deposited under different pressure of the gas is 4.33 eV. The refractive index (n) behaves as normal dispersion and decreases with increasing the pressure of the gas. The dispersion energy and single oscillator energy increase with increasing the pressure of the gas whereas the optical conductivity decreases with increasing the power on Sb target.
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