... Fig. 5. The effect of creep temperature on the average particle size (4 after creep deformati... more ... Fig. 5. The effect of creep temperature on the average particle size (4 after creep deformation, the average growth rate (d) after creep test, and X-ray linewidth of a and grains for a ) Zn-40 wt% A1 and b) Zn-0.5 wt% A1 Page 6. 566 MS SAKR, A. EE ABDEL-RAHIEM, and A. A. EL ...
The electronic structure and magnetic properties of Fe 3 O 4 have been studied by density functio... more The electronic structure and magnetic properties of Fe 3 O 4 have been studied by density functional method in the frame of local density approximation. Gradually reducing the symmetry has been used to establish different cation distribution of the studied compound. This symmetry cracking introduces some evidences for the half-metallicity of Fe 3 O 4. Different experimental distributions, of cations Fe +2 and Fe +3 between tetrahedral A-site and octahedral B-site for spinel structure, have been calculated. The magnetic anisotropy through the spin-orbit coupling (SOC) has been calculated, where the results revealed a pronounced agreement with the experimental results. These SOC calculations have been conducted for different directions of the magnetization, where semiconductor and metallic behavior for majority and minority channels, respectively, are still found respectively. As for Fe in B-site, the spin orbital angular momentum coupling component of the magnetic momentis considerably larger than that for Fe in A-site. This urges some states of Fe-3d electrons on B-siteto have higher energy states than the Fermi energy.
Applied Physics A Materials Science & Processing, 1995
... r/ne. (2) The mobility was calculated over a wide range of temper-atures (300-773 K) forCul-~... more ... r/ne. (2) The mobility was calculated over a wide range of temper-atures (300-773 K) forCul-~TixFe204 with 0 ~< x ~< 0.5. ... References 1. NF Mott: Metal-Insulator Transitions (Taylor &Francis, London 1990) 2. TE Whall, KK Yeung, YG Proykova, VAM Brabers: Philos. Mag. ...
Numerically large Hall and magnetoresistance coefficients are reported for very dilute alloys of ... more Numerically large Hall and magnetoresistance coefficients are reported for very dilute alloys of A£ containing the 3d impurities Ti and V. The Hall results are unexpected for substitutional impurities. The giant magnetoresistance coefficients are shown to result from strong electron scattering anisotropy, not between second zone holes and third zone electrons, but from strong interaction between plane wave states on the free electron portion of the Fermi surface and the 3d virtual bound state.
A problem for an infinite thermoelastic solid weakened by an internal penny-shaped crack has been... more A problem for an infinite thermoelastic solid weakened by an internal penny-shaped crack has been solved. The solid that is assumed to be homogeneous and isotropic is subjected to temperature and stress distributions. A cylindrical system of coordinates is used, in which the plane z = 0 is that of the crack and the z-axis is normal to it at the centre. In addition, the crack occupies the region z = 0, 0 < r < a that is subjected to prescribed temperature and stress distributions which vary with the radial distance r. The problem is solved using the Hankel transform. The boundary conditions of the problem give a set of two dual integral equations, which are solved analytically. The inversion of the transform is then obtained analytically. Numerical results for the temperature, stress and displacements distributions are shown graphically and then discussed. All the definite integrals involved were calculated using Romberg technique of numerical integration with the aid of a Fort...
ABSTRACT A two-dimensional problem for an infinite space weakened by a finite linear opening Mode... more ABSTRACT A two-dimensional problem for an infinite space weakened by a finite linear opening Mode-I crack is solved. The solid material is assumed to be homogeneous and isotropic. The crack is subjected to prescribed temperature and stress distributions. A rectangular system of Cartesian coordinates is used. The Fourier transform technique is applied to solve the problem. The boundary conditions of the problem are then reduced to a system of two dual integral equations, which are solved analytically. Numerical values for the temperature, stress and displacements are obtained and represented graphically then discussed. All the definite integrals involved were calculated using Romberg technique of numerical integration with the aid of a Fortran program compiled with Visual Fortran v.6.1 on a Pentium-IV pc with processor speed 2.0 GHz.
Thin films of different thicknesses of Se 90 S 10-x Cd x , (x=0 and 5) were deposited by thermal ... more Thin films of different thicknesses of Se 90 S 10-x Cd x , (x=0 and 5) were deposited by thermal evaporation technique onto glass substrates. X-ray diffraction patterns (XRD), differential thermal analysis (DTA) and energy dispersive X-ray spectroscopy (EDX) studies were carried out for samples in powder and thin film forms. XRD indicates that all the deposited thin films have an amorphous structure. The transmittance at normal incidence for these films was measured in the wavelength range 350-2500 nm. Applying Swanepoel's method successfully enabled to determine, with high accuracy, the film thickness, the real index of refraction and imaginary part of index of refraction. Regarding the optical absorption measurements; the type of optical transition and optical band gap were estimated as a function of photon energy. The effect of Cd addition on the refractive index, absorption coefficient and the optical band gap were investigated. The high frequency dielectric constant, the single oscillator energy, the dispersion energy and refractive index dispersion parameter were evaluated. Solar cell criterions have been considered. The results are interpreted in terms of concentration of localized states.
ABSTRACT Thin films of HgTe were thermally, flash, evaporated onto glass substrates at room tempe... more ABSTRACT Thin films of HgTe were thermally, flash, evaporated onto glass substrates at room temperature. The structural investigations showed that stoichiometric and amorphous films were produced. The electrical resistivity, thermoelectric power and space charge characteristics were also studied at room and elevated temperatures. The measurements indicated that HgTe thin films behave as a p-type semiconductor with current carrier concentration between 1021 and 1025m−3. Two conduction mechanisms were applied to interpret the obtained results.
... Fig. 5. The effect of creep temperature on the average particle size (4 after creep deformati... more ... Fig. 5. The effect of creep temperature on the average particle size (4 after creep deformation, the average growth rate (d) after creep test, and X-ray linewidth of a and grains for a ) Zn-40 wt% A1 and b) Zn-0.5 wt% A1 Page 6. 566 MS SAKR, A. EE ABDEL-RAHIEM, and A. A. EL ...
... acceptors. Moamen S. Refat a , b , Corresponding Author Contact Information , E-mail The Corr... more ... acceptors. Moamen S. Refat a , b , Corresponding Author Contact Information , E-mail The Corresponding Author , A. Elfalaky c and Eman Elesh d. a Department of Chemistry, Faculty of Science, Port Said University, Port Said, Egypt. ...
Generalized gradient approximation (GGA) and GGA + U (U is the Hubbard parameter) were applied to... more Generalized gradient approximation (GGA) and GGA + U (U is the Hubbard parameter) were applied to scrutinize the electronic structure and magnetic properties of the spinel ferrite MnFe 2 O 4 . Compression between GGA and GGA + U calculations were carried out. Oxygen position (z), total unit crystal spin magnetic moment, and lattice parameters were optimized. The optimized structure parameters are in good agreement with the experimental values. The experimental results described by the GGA + U calculations are better than the normal frame work. A new method for calculating U has been introduced. The calculations show that Mn ferrite has cubic structure with ordered spins. The compound should experience insulating behaviors which is experimentally observed. Such insulating behavior and spin ordering increase the ability of using Mn ferrite in high frequency applications. The moments are predominantly due to the ionic model behaviors for this compound. High spin state is favorable for the two cations Mn and Fe. From the anomalous explanation of DOS it is observed that, a ferrimagnetic spin current between Fe-3d and Mn-3d through O-2p is yielded. The flat bands, which are the more atomic-like lead to a high density of states and magnetic instability of local moment character. The effect of decreasing octahedral point group from O h to D 4h , C 4v and C 3v were carried out. The octahedral deformation has not been found in Mn ferrite. Total picture study for Hubbard parameter U has been carried out where accurate value for U was determined by comparing the energy gap with that obtained experimentally. Correlated behavior was proved for Manganese ferrite. j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j a l c o m
The European Physical Journal Applied Physics, 2001
ABSTRACT Stoichiometric In2S3 films were prepared by thermal evaporation technique onto clean gla... more ABSTRACT Stoichiometric In2S3 films were prepared by thermal evaporation technique onto clean glass substrates. According to X-ray investigations, the as-deposited films were in amorphous state. Both the ac conductivity and dielectric constants were measured in the frequency range 100 Hz-100 kHz at different temperatures. Different parameters such as the frequency exponent parameter s, the density of states near the Fermi level N(E_F), the activation energy (Delta E) and the optical band gap E_g of In2S3 amorphous thin films were estimated. The hopping conduction was recognized as the conduction mechanism for the investigated films.
The deviation from Matthiessen's rule has been investigated. The calculations were based upon thr... more The deviation from Matthiessen's rule has been investigated. The calculations were based upon three group model, in which the Fermi surface is split up into three regions. The mean free paths over the three major regions are denoted by L1, Lz and L3. Besides the Fermi surface anisotropy, the anisotr0py of electron scattering with phonons and impurities have also been employed in the calculations.
The mixed ferrites Cul+~TixFe2_2~O4 with x = 0, 0.1, 0.2, 0.3 and 0.4 were prepared by standard c... more The mixed ferrites Cul+~TixFe2_2~O4 with x = 0, 0.1, 0.2, 0.3 and 0.4 were prepared by standard ceramic techniques. Both structural and IR investigations were carried out. The X-ray diffraction pattern showed that the prepared samples are pure spinels. It is also indicated that the system exists in two crystallographic forms, the tetragonal structure (for x = 0, 0.1) and the cubic structure (for the rest of x).
... Fig. 5. The effect of creep temperature on the average particle size (4 after creep deformati... more ... Fig. 5. The effect of creep temperature on the average particle size (4 after creep deformation, the average growth rate (d) after creep test, and X-ray linewidth of a and grains for a ) Zn-40 wt% A1 and b) Zn-0.5 wt% A1 Page 6. 566 MS SAKR, A. EE ABDEL-RAHIEM, and A. A. EL ...
The electronic structure and magnetic properties of Fe 3 O 4 have been studied by density functio... more The electronic structure and magnetic properties of Fe 3 O 4 have been studied by density functional method in the frame of local density approximation. Gradually reducing the symmetry has been used to establish different cation distribution of the studied compound. This symmetry cracking introduces some evidences for the half-metallicity of Fe 3 O 4. Different experimental distributions, of cations Fe +2 and Fe +3 between tetrahedral A-site and octahedral B-site for spinel structure, have been calculated. The magnetic anisotropy through the spin-orbit coupling (SOC) has been calculated, where the results revealed a pronounced agreement with the experimental results. These SOC calculations have been conducted for different directions of the magnetization, where semiconductor and metallic behavior for majority and minority channels, respectively, are still found respectively. As for Fe in B-site, the spin orbital angular momentum coupling component of the magnetic momentis considerably larger than that for Fe in A-site. This urges some states of Fe-3d electrons on B-siteto have higher energy states than the Fermi energy.
Applied Physics A Materials Science & Processing, 1995
... r/ne. (2) The mobility was calculated over a wide range of temper-atures (300-773 K) forCul-~... more ... r/ne. (2) The mobility was calculated over a wide range of temper-atures (300-773 K) forCul-~TixFe204 with 0 ~< x ~< 0.5. ... References 1. NF Mott: Metal-Insulator Transitions (Taylor &Francis, London 1990) 2. TE Whall, KK Yeung, YG Proykova, VAM Brabers: Philos. Mag. ...
Numerically large Hall and magnetoresistance coefficients are reported for very dilute alloys of ... more Numerically large Hall and magnetoresistance coefficients are reported for very dilute alloys of A£ containing the 3d impurities Ti and V. The Hall results are unexpected for substitutional impurities. The giant magnetoresistance coefficients are shown to result from strong electron scattering anisotropy, not between second zone holes and third zone electrons, but from strong interaction between plane wave states on the free electron portion of the Fermi surface and the 3d virtual bound state.
A problem for an infinite thermoelastic solid weakened by an internal penny-shaped crack has been... more A problem for an infinite thermoelastic solid weakened by an internal penny-shaped crack has been solved. The solid that is assumed to be homogeneous and isotropic is subjected to temperature and stress distributions. A cylindrical system of coordinates is used, in which the plane z = 0 is that of the crack and the z-axis is normal to it at the centre. In addition, the crack occupies the region z = 0, 0 < r < a that is subjected to prescribed temperature and stress distributions which vary with the radial distance r. The problem is solved using the Hankel transform. The boundary conditions of the problem give a set of two dual integral equations, which are solved analytically. The inversion of the transform is then obtained analytically. Numerical results for the temperature, stress and displacements distributions are shown graphically and then discussed. All the definite integrals involved were calculated using Romberg technique of numerical integration with the aid of a Fort...
ABSTRACT A two-dimensional problem for an infinite space weakened by a finite linear opening Mode... more ABSTRACT A two-dimensional problem for an infinite space weakened by a finite linear opening Mode-I crack is solved. The solid material is assumed to be homogeneous and isotropic. The crack is subjected to prescribed temperature and stress distributions. A rectangular system of Cartesian coordinates is used. The Fourier transform technique is applied to solve the problem. The boundary conditions of the problem are then reduced to a system of two dual integral equations, which are solved analytically. Numerical values for the temperature, stress and displacements are obtained and represented graphically then discussed. All the definite integrals involved were calculated using Romberg technique of numerical integration with the aid of a Fortran program compiled with Visual Fortran v.6.1 on a Pentium-IV pc with processor speed 2.0 GHz.
Thin films of different thicknesses of Se 90 S 10-x Cd x , (x=0 and 5) were deposited by thermal ... more Thin films of different thicknesses of Se 90 S 10-x Cd x , (x=0 and 5) were deposited by thermal evaporation technique onto glass substrates. X-ray diffraction patterns (XRD), differential thermal analysis (DTA) and energy dispersive X-ray spectroscopy (EDX) studies were carried out for samples in powder and thin film forms. XRD indicates that all the deposited thin films have an amorphous structure. The transmittance at normal incidence for these films was measured in the wavelength range 350-2500 nm. Applying Swanepoel's method successfully enabled to determine, with high accuracy, the film thickness, the real index of refraction and imaginary part of index of refraction. Regarding the optical absorption measurements; the type of optical transition and optical band gap were estimated as a function of photon energy. The effect of Cd addition on the refractive index, absorption coefficient and the optical band gap were investigated. The high frequency dielectric constant, the single oscillator energy, the dispersion energy and refractive index dispersion parameter were evaluated. Solar cell criterions have been considered. The results are interpreted in terms of concentration of localized states.
ABSTRACT Thin films of HgTe were thermally, flash, evaporated onto glass substrates at room tempe... more ABSTRACT Thin films of HgTe were thermally, flash, evaporated onto glass substrates at room temperature. The structural investigations showed that stoichiometric and amorphous films were produced. The electrical resistivity, thermoelectric power and space charge characteristics were also studied at room and elevated temperatures. The measurements indicated that HgTe thin films behave as a p-type semiconductor with current carrier concentration between 1021 and 1025m−3. Two conduction mechanisms were applied to interpret the obtained results.
... Fig. 5. The effect of creep temperature on the average particle size (4 after creep deformati... more ... Fig. 5. The effect of creep temperature on the average particle size (4 after creep deformation, the average growth rate (d) after creep test, and X-ray linewidth of a and grains for a ) Zn-40 wt% A1 and b) Zn-0.5 wt% A1 Page 6. 566 MS SAKR, A. EE ABDEL-RAHIEM, and A. A. EL ...
... acceptors. Moamen S. Refat a , b , Corresponding Author Contact Information , E-mail The Corr... more ... acceptors. Moamen S. Refat a , b , Corresponding Author Contact Information , E-mail The Corresponding Author , A. Elfalaky c and Eman Elesh d. a Department of Chemistry, Faculty of Science, Port Said University, Port Said, Egypt. ...
Generalized gradient approximation (GGA) and GGA + U (U is the Hubbard parameter) were applied to... more Generalized gradient approximation (GGA) and GGA + U (U is the Hubbard parameter) were applied to scrutinize the electronic structure and magnetic properties of the spinel ferrite MnFe 2 O 4 . Compression between GGA and GGA + U calculations were carried out. Oxygen position (z), total unit crystal spin magnetic moment, and lattice parameters were optimized. The optimized structure parameters are in good agreement with the experimental values. The experimental results described by the GGA + U calculations are better than the normal frame work. A new method for calculating U has been introduced. The calculations show that Mn ferrite has cubic structure with ordered spins. The compound should experience insulating behaviors which is experimentally observed. Such insulating behavior and spin ordering increase the ability of using Mn ferrite in high frequency applications. The moments are predominantly due to the ionic model behaviors for this compound. High spin state is favorable for the two cations Mn and Fe. From the anomalous explanation of DOS it is observed that, a ferrimagnetic spin current between Fe-3d and Mn-3d through O-2p is yielded. The flat bands, which are the more atomic-like lead to a high density of states and magnetic instability of local moment character. The effect of decreasing octahedral point group from O h to D 4h , C 4v and C 3v were carried out. The octahedral deformation has not been found in Mn ferrite. Total picture study for Hubbard parameter U has been carried out where accurate value for U was determined by comparing the energy gap with that obtained experimentally. Correlated behavior was proved for Manganese ferrite. j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j a l c o m
The European Physical Journal Applied Physics, 2001
ABSTRACT Stoichiometric In2S3 films were prepared by thermal evaporation technique onto clean gla... more ABSTRACT Stoichiometric In2S3 films were prepared by thermal evaporation technique onto clean glass substrates. According to X-ray investigations, the as-deposited films were in amorphous state. Both the ac conductivity and dielectric constants were measured in the frequency range 100 Hz-100 kHz at different temperatures. Different parameters such as the frequency exponent parameter s, the density of states near the Fermi level N(E_F), the activation energy (Delta E) and the optical band gap E_g of In2S3 amorphous thin films were estimated. The hopping conduction was recognized as the conduction mechanism for the investigated films.
The deviation from Matthiessen's rule has been investigated. The calculations were based upon thr... more The deviation from Matthiessen's rule has been investigated. The calculations were based upon three group model, in which the Fermi surface is split up into three regions. The mean free paths over the three major regions are denoted by L1, Lz and L3. Besides the Fermi surface anisotropy, the anisotr0py of electron scattering with phonons and impurities have also been employed in the calculations.
The mixed ferrites Cul+~TixFe2_2~O4 with x = 0, 0.1, 0.2, 0.3 and 0.4 were prepared by standard c... more The mixed ferrites Cul+~TixFe2_2~O4 with x = 0, 0.1, 0.2, 0.3 and 0.4 were prepared by standard ceramic techniques. Both structural and IR investigations were carried out. The X-ray diffraction pattern showed that the prepared samples are pure spinels. It is also indicated that the system exists in two crystallographic forms, the tetragonal structure (for x = 0, 0.1) and the cubic structure (for the rest of x).
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Papers by Ahmed Elfalaky