M. A. Hefni

Optical investigations on InxSe1−x thin films (II)

Abstract Thin films of In0.10Se90 of thickness ∾200 A are prepared by vacuum evaporation. The optical gaps (Eoptg) and the high-frequency dielectric constant (eϵ∞) are determined from the absorption spectrum of the In0.10Se0.90 films heat-treated at different temperatures. The effect of the temperature of heat treatment on the optical gap (Eoptg) and the high-frequency dielectric constant (eϵ∞) of the films is interpreted in terms of the density of state model of Mott and Davis and explained as being due to the saturation of bonds in the amorphous solid. It is shown that in the case of In0.10Se0.90 a transition from the amorphous to the crystalline state takes place at ∾373 K. The structural analysis of In0.10Se0.90 films by using XRD is reported.

Spectroscopic studies and electrical conductivity behavior of γ-irradiated Li2SO4—Na2SO4 mixed system

Abstract The Li2SO4—Na2SO4 mixed system was prepared by the precipitation technique. Electron paramagnetic resonance (EPR) spectra of the γ-irradiated Li2SO4—Na2SO4 mixed system were measured at room temperature. Two types of centers, A and B, identified as SO− 3 and SO− 4, respectively were studied. The SO− 3 center is characterized by an intense isotropic signal with a g-value ≈ 2.0029, while the SO− 4 center appears as a weak and broad signal with a g-value of 2.02. Infrared spectra were recorded for unirradiated and γ-irradiated samples. A decrease in the intensity of the IR spectra was observed after irradiation. The electrical conductivity, σ, was measured for the Li2SO4—Na2SO4 system before and after γ-irradiation in the temperature range from 30 up to 430°C. A considerable decrease in the conductivity value accompanied by an increase in the activation energy was observed after gamma irradiation. The energy of formation of Frenkel defects was estimated to be 3.2eV. The current-voltage characteristics were measured at different temperatures in order to estimate the type of conduction in the samples. Isothermal annealing kinetics were investigated at different temperatures before and after γ-irradiation.

Applications of the three points analysis method for obtaining the trap parameters and the separation of thermoluminescence glow curve into its components

Here, we apply a recently developed technique to separate a composite thermoluminescence (TL) glow curve into its individual components and to evaluate the trap parameters of the individual TL glow peaks. These parameters include the order of kinetics b, the activation energy E (eV) and the frequency factor S (s−1) or the pre-exponential factor S″ (s−1). Recently, a general equation was developed to estimate the order of kinetics b. The characteristic point of this equation is that any set of three data points in a TL glow curve can yield b. Using this characteristic, an improved procedure was suggested to separate a composite glow curve, which includes several overlapping peaks, into its individual components and to obtain the trap parameters of the individual glow peaks. The method was applied here to analyze and determine the trap parameters of the TL glow curve of the promising TL dosimetric material, double potassium yttrium fluoride (K2YF5) doped with praseodymium ions (Pr3+), in response to γ-irradiation.

D.C. conduction phenomenon and spectrum of a novel bis(7-formyl-8-hydroxyquinoline) zinc complex

A novel bis(7-formyl-8-hydroxyquinoline)zinc complex was prepared from 7-formyl-8-hydroxyquinoline. This compound was characterized on the basis of elemental analysis, i.r., 1H nuclear magnetic resonance, magnetic moment and conductivity measurements. The compound was a non-conductor in dimethylformamide. A tentative structure for this compound is suggested. The electrical conductivity at various temperatures for an annealing time of 1 h has been measured. The activation energy of this compound is found to be 0.68 eV. Conduction parameters including the Schottky coefficient (βs), Schottky electrode barrier (φs), jump distance (d) and dielectric constant (ɛ) have been determined. The aim of this study is also to understand the mechanism of conduction of this zinc(II) complex.

Short and intermediate range order of Ge20Se80−xTex glasses

The total structure factor, S(K), have been obtained for the chalcogenide Ge20Se80−xTex (where x=0, 10, 20, and 30 at. %) glasses using x-ray diffraction in the wave vector interval 0.28≤K≤6.87 A−1. The appearance of the first sharp diffraction peak in the structure factor indicates the presence of the intermediate range order. The radii of the first- and second-coordination shells (r1,r2) are increased linearly with Te addition. The large covalent radius of Te atom in compare with that of Se atom was behind the above linear increase. The first coordination number shows insignificant changes with Te content. The obtained values of r1/r2 ratio and the corresponding bond angle (Θ) indicate that the structural units inside the present alloys are Ge(Se1/2)4 tetrahedra connected by chains of the chalcogen atoms. Raman spectra confirm the above conclusion and in the same time exclude the existence of Ge(Te1/2)4 tetrahedra. Based on the chemical ordered network mode, Te–Te bonds are responsible for the different...

Electron paramagnetic resonance, infrared, and electrical conductivity studies of γ-ray irradiated Li2SO4-K2SO4 mixed system

Abstract Electron paramagnetic resonance spectra of 7-irradiated Li:2SO4-K2SO4 mixed system are measured at X-band and 300 K. Two types of centers, A and B, identified as LiOH+ 2 and SO− 3 are studied. The EPR spectrum of LiOH+ 2 has a well-resolved hyperfine structure. The effective g-value and the hyperfine structure constant of it are calculated. On the other hand, the SO− 3 center is characterized by an intense isotropic signal at a g-value ≈ 2. 0035. Mechanisms of center formation are proposed. Infrared transmittance spectra were recorded for unirradiated and γ-ray irradiated samples. A decrease in the transmittance spectra was observed after irradiation. The ionic conductivity, σ, has been measured for the Li2SO4-K2SO4 system before and after irradiation in the temperature range 30–400°C. The activation energy was found to be 1. 1 eV. A considerable decrease in the conductivity value accompanied by an increase in the activation energy was observed after γ-irradiation.

γ-irradiation effect on the spectroscopic and electrical properties of K2SO4—Na2SO4 mixed system

Abstract Measurements of electron paramagnetic resonance, infrared and electrical properties were carried out for the K2SO4—Na2SO4 mixed system before and after γ-irradiation. EPR measurements revealed the presence of a quartet of lines characterized by an isotropic g-value of 2.0034. These lines are mainly attributed to the formation of a SO− 3 center which results from the interaction of γ-rays with the sulfate ion. A decrease in the absorption intensity of the Infrared radiation was observed after γ-irradiation due to radiation damage in the sulfate group. The electrical conductivity, σ, was measured for the K2SO4—Na2SO4 system before and after γ-irradiation in the temperature range from 30 up to 430°C. A considerable decrease in the conductivity value accompanied by an increase in the activation energy was observed after γ-irradiation. The energy of formation of Frenkel defects was estimated to be 2.94eV. The current-voltage characteristics were measured at different temperatures in order to estimate the type of conduction in the samples. Isothermal annealing kinetics was investigated at different temperatures before and after γ-irradiation. The electrical conductivity decreases with increasing time of annealing and the annealing process is dominated by a unique rate process.

DSC and electrical conductivity studies of (Li1-xKx)2SO4 mixed crystals

Abstract (Li1−Kx)2SO4 mixed crystals were prepared by the precipitation technique where x = 0.5, 0.7, 0.9 and 0.99. The phase transformations of the mixed crystals have been analyzed by the DSC technique. The DSC curves of (Li1−xKx)2SO4 mixed crystals reveal that as the potassium content increases the first high temperature phase of the intermediate LiKSO4 phase at T = 436°C disappears and a two- phase mixture of LiKSO4 and K2SO4 is found for x = 0.7 and 0.9. It is observed from the electrical conductivity measurements of (Li1−xKx)2SO4 mixed crystals that the electrical conductivity increases as the K2SO4 concentration increases with average activation energy of 1.04 eV. The enhancement in the electrical conductivity is primarily a result of the presence of two ionically conducting constituents and the formation of a diffuse space charge layer at the interface region between these two phases.

EPR Studies of the Low-Tempehature Phase Transitions in LiKSO4 by Cu2+ Ions

Abstract Electron paramagnetic resonance (EPR) spectra of Cu2+ doped lithium potassium sulphate (LP3) have been studied at different temperatures. The spin-Hamiltonian g and A parameters have been evaluated. Phase transitions in LP3 were observed at low temperature. The measured g-values indicate a rhombic field for Cu2+ in the lattice at the temperature range 300–215 K. Between 215 K and 123 K an orthorhombic field suggested. The bonding parameter (∞2), Fermi-contact term (K) and the free ion dipolar term (P) are evaluated using the principal g and A values. The ground state were runction for Cu2+ ion in (LPS) is determined. ∗Present address: Physics Department, Faculty of Science, Sana1 a University, Sana1 a P.O. Box 15764 Yemen.