Hisham Widatallah | Sultan Qaboos University (original) (raw)
Papers by Hisham Widatallah
We study the effect of hydrogen on the electronic, magnetic and hyperfine structures of an iron-v... more We study the effect of hydrogen on the electronic, magnetic and hyperfine structures of an iron-vanadium superlattice consisting of three Fe monolayers and nine V monolayers. The contact charge density (ρ), the contact hyperfine field (B hf) and the electronic field gradient (EFG) at the Fe sites for different H locations and H fillings are calculated using the first principle full-potential linear-augmented-plane-wave (FP-LAPW) method.
Abstract Spinel-related aluminum-substituted Li0. 5Fe2. 5O4 has been synthesized by heating a mix... more Abstract Spinel-related aluminum-substituted Li0. 5Fe2. 5O4 has been synthesized by heating a mixture of aluminum-substituted corundum-related α-Fe2O3 with Li2CO3 at 700 C which is ca. 450-500 C lower than temperatures at which the material is normally prepared with conventional ceramic methods. Rietveld structural refinement of the X-ray diffraction data is in favour of a model in which Al3+ ions exclusively occupy octahedral sites replacing Fe3+ and Li+ with some replaced Li+ ions substituting for Fe3+ at tetrahedral sites.
Abstract Spinel-related titanium-substituted Li0. 5Fe2. 5O4 has been synthesised by heating a mix... more Abstract Spinel-related titanium-substituted Li0. 5Fe2. 5O4 has been synthesised by heating a mixture of titaniumdoped corundum-related α-Fe2O3 with Li2CO3 at 850 C which is ca. 250-350 C lower than temperatures at which the material is normally prepared conventionally. Mössabuer and magnetic measurements imply that the Ti4+ ions substitute for octahedral Fe3+ ions. Interatomic potential calculations support this substitution with the charge balance being maintained by Li+ vacancies.
Spinel-related magnesium-doped Li0. 5Fe2. 5O4 has been synthesised by heating magnesium-substitut... more Spinel-related magnesium-doped Li0. 5Fe2. 5O4 has been synthesised by heating magnesium-substituted corundum-related α-Fe2O3 with Li2CO3 at 600° C which is ca. 600° C lower than the temperature normally used to prepare metal-doped Li0. 5Fe2. 5O4 by conventional sintering methods. Rietveld structure refinement of the X-ray powder diffraction data shows that the Mg2+ ions substitute for Fe3+ ions on the tetrahedral sites whilst the Li+ ions are located on the octahedral sites.
The defect structure of lithiated tin-and titanium-doped α-Fe2O3 has been assessed using interato... more The defect structure of lithiated tin-and titanium-doped α-Fe2O3 has been assessed using interatomic potential calculations. Of the models considered for lithiation, a model in which Li+ occupies an interstitial site balanced by the reduction of Fe3+ to Fe2+ on an Fe3+ site was found to be more favourable than the substitution of Li+ on an Fe3+ octahedral site balanced by an O2− vacancy. Insertion of lithium into the interstitial site between two adjacent M4+ ions was particularly favourable.
Abstract The influence of mechanical alloying and subsequent sintering of a 1: 1 molar mixture of... more Abstract The influence of mechanical alloying and subsequent sintering of a 1: 1 molar mixture of Eu2O3 and Cr2O3 on the formation of EuCrO3 perovskite-related nanocrystalline particles is investigated. Pre-milling the mixture for (75 h) has led to the formation of nanocrystalline EuCrO3 particles (~ 25 nm) at 900oC (12 h). This temperature is~ 300ºC-400ºC lower than those at which the material is prepared via the conventional solid state routes.
There has been considerable interest in the insertion of lithium into iron oxides of the type LiF... more There has been considerable interest in the insertion of lithium into iron oxides of the type LiFeO 2 [1] and [2] and Fe 3 O 4 [3] because of the potential for Li + ion mobility within the rigid three-dimensional host such that the materials might be suitable as electrodes in battery applications. We have recently prepared materials of the type α-Fe 2−x M x O 3 (M=Ti, Sn, Mg) [4] and [5].
Abstract A quaternionic mass defining longitudinal mass () and transverse mass () of a particle i... more Abstract A quaternionic mass defining longitudinal mass () and transverse mass () of a particle is introduced. The longitudinal and transverse masses represent the mass of the particle and matter wave accompanying it, respectively. A massive particle is found to have a bigger longitudinal mass than transverse mass. The particle nature due to the transverse mass of a particle is described by a scalar wave satisfying the Klein-Gordon equation. The transverse mass vector is found to be along the direction of the particle's velocity ().
Abstract—A newly fallen Sudanese meteorite named Al Zarnkh was investigated using room and liquid... more Abstract—A newly fallen Sudanese meteorite named Al Zarnkh was investigated using room and liquid nitrogen temperature Mössbauer measurements, X-ray diffraction (XRD), and electron probe microanalysis (EPMA) in conjunction with energy dispersive X-ray microscopy. The Mössbauer spectra exhibited strong paramagnetic doublets with magnetic sextets. The doublets are assigned to olivine and pyroxene, while the magnetic sextets are assigned to troilite and kamacite.
Chromium and manganese co-substituted spinel magnesioferrites of the composition Mg 1− x Mn x Fe2... more Chromium and manganese co-substituted spinel magnesioferrites of the composition Mg 1− x Mn x Fe2− 2 x Cr 2x O 4 (x= OO, 0.1, 0.2, 0.3, and 0.5) were investigated with X-ray diffraction (XRD), Mössbauer spectroscopy and magnetic measurements. The cation distribution inferred suggests that Mn 2+ and Cr 3+ ions dominantly occupy the A-and Bsites respectively. The gradual decrease of the hyperfine fields and Curie temperatures with increasing x reflects a gradual weakening in the AB exchange interaction.
Abstract The crystal structure and magnetic properties of the spinel system MgFe 2− x Cr x O 4 (w... more Abstract The crystal structure and magnetic properties of the spinel system MgFe 2− x Cr x O 4 (with x= 0, 0.2, 0.4, 0.6, 0.8, 1.0) have been investigated by means of X-ray diffraction (XRD), and Mössbauer spectroscopy. The XRD patterns showed the samples were single-phase cubic spinels. The 295 K Mössbauer spectra of the studied samples showed a continuous collapse of the internal magnetic field for both tetrahedral (A) and octahedral [B] sites with increasing Cr contents.
Abstract Single-phased spinel-related titanium-substituted Li 0.5 Fe 2.5 O 4 has been synthesized... more Abstract Single-phased spinel-related titanium-substituted Li 0.5 Fe 2.5 O 4 has been synthesized by sintering in air a mechanically pre-milled mixture of lithium carbonate, corundum-related iron (III) oxide and the rutile polymorph of titanium (IV) oxide at 700 C (12 h). This temperature is ca. 450–500 C less than the temperatures at which the material is normally prepared by conventional ceramic techniques.
Abstract A structural and Mössbauer study of mechanosynthesized EuCr 1− x Fe x O 3 nanocrystallin... more Abstract A structural and Mössbauer study of mechanosynthesized EuCr 1− x Fe x O 3 nanocrystalline particles (∼ 20–30 nm) is presented. The lattice parameters increase with increasing x-value leading to an increasingly distorted structure. The crystallite sizes range between 20 nm and 30 nm. Magnetic and 57 Fe Mössbauer measurements show the samples with x< 0.7 to be paramagnetic and those with x≥ 0.7 to be partially superparamagnetic at 298 K.
Solid state …, Jan 1, 2002
Tin-and titanium-doped α-Cr2O3 have been prepared by the calcination of precipitates. Rietveld st... more Tin-and titanium-doped α-Cr2O3 have been prepared by the calcination of precipitates. Rietveld structure refinement of the X-ray powder diffraction patterns shows that the dopant metals occupy interstitial sites and partially substitute on octahedral chromium sites in the corundum-related α-Cr2O3 structure. Interatomic potential calculations show that such defects are energetically more favourable than the exclusive substitution of chromium or the occupation by the dopant of interstitial sites in α-Cr2O3 with charge balance being ...
Solid state communications, Jan 1, 2001
A study of the crystallographic structure and magnetic properties of the double perovskites Ba 2 ... more A study of the crystallographic structure and magnetic properties of the double perovskites Ba 2 MnMoO 6 and Sr 2 MnMoO 6 in polycrystalline form has been carried out by means of neutron powder diffraction (NPD) and magnetization measurements. The Rietveld analysis of room temperature data shows that the Mn 2+ and Mo 6+ ions are B-site ordered, i.e. the structure is a NaCl-type ordered double perovskite. Ba 2 MnMoO 6 crystallizes in the cubic space group Fm3m (a = 8.1680(1)) and Sr 2 MnMoO 6 crystallizes in the space group P4 2 /n (a = 7.9575(5), c = 7.9583(9)). Bond valence sum (BVS) calculation revealed that these compounds have the valency pair of {Mn 2+ (3d 5 ;t 3 2g e 2 g ), Mo 6+ (4d 0 )}. The magnetic measurements suggest that these compounds transform to an antiferromagnetic state below 10 K.
Journal of Physics: …, Jan 1, 2010
Single-phased spinel-related Ti 4+ -substituted Li 0.5 Fe 2.5 O 4 has been synthesized by the hea... more Single-phased spinel-related Ti 4+ -substituted Li 0.5 Fe 2.5 O 4 has been synthesized by the heating mixture of hydrothermally prepared Ti 4+ -substituted α-Fe 2 O 3 and Li 2 CO 3 at 850°C (12 h). This temperature is ca. 250-350°C lower than those at which the material is conventionally prepared by the ceramic techniques. X-ray diffraction was used to analyze the evolution of the formation process and, in conjunction with Mössbauer and magnetization measurements, to determine the cation distribution of the resulting ferrite. The results imply that the Ti 4+ ions substitute for Fe 3+ ones at the octahedral (B) sites whilst the excess Li + ions, required for balancing the charge in the spinel-related structure, replace Fe 3+ ions at the tetrahedral (A) sites.
Journal of Solid State Chemistry, Jan 1, 2002
Solid state …, Jan 1, 2002
Chinese Physics Letters, Jan 1, 2010
A generalized continuity equation extending the ordinary continuity equation has been found using... more A generalized continuity equation extending the ordinary continuity equation has been found using quanternions. It is shown to be compatible with Dirac, Schrodinger, Klein-Gordon and diffusion equations. This generalized equation is Lorentz invariant. The transport properties of electrons are found to be governed by Schrodinger-like equation and not by the diffusion equation.
Journal of Physics and Chemistry of …, Jan 1, 2002
The defect structure of lithiated tin-and titanium-doped α-Fe2O3 has been assessed using interato... more The defect structure of lithiated tin-and titanium-doped α-Fe2O3 has been assessed using interatomic potential calculations. Of the models considered for lithiation, a model in which Li+ occupies an interstitial site balanced by the reduction of Fe3+ to Fe2+ on an Fe3+ site was found to be more favourable than the substitution of Li+ on an Fe3+ octahedral site balanced by an O2− vacancy. Insertion of lithium into the interstitial site between two adjacent M4+ ions was particularly favourable. The calculated lattice parameters ...
We study the effect of hydrogen on the electronic, magnetic and hyperfine structures of an iron-v... more We study the effect of hydrogen on the electronic, magnetic and hyperfine structures of an iron-vanadium superlattice consisting of three Fe monolayers and nine V monolayers. The contact charge density (ρ), the contact hyperfine field (B hf) and the electronic field gradient (EFG) at the Fe sites for different H locations and H fillings are calculated using the first principle full-potential linear-augmented-plane-wave (FP-LAPW) method.
Abstract Spinel-related aluminum-substituted Li0. 5Fe2. 5O4 has been synthesized by heating a mix... more Abstract Spinel-related aluminum-substituted Li0. 5Fe2. 5O4 has been synthesized by heating a mixture of aluminum-substituted corundum-related α-Fe2O3 with Li2CO3 at 700 C which is ca. 450-500 C lower than temperatures at which the material is normally prepared with conventional ceramic methods. Rietveld structural refinement of the X-ray diffraction data is in favour of a model in which Al3+ ions exclusively occupy octahedral sites replacing Fe3+ and Li+ with some replaced Li+ ions substituting for Fe3+ at tetrahedral sites.
Abstract Spinel-related titanium-substituted Li0. 5Fe2. 5O4 has been synthesised by heating a mix... more Abstract Spinel-related titanium-substituted Li0. 5Fe2. 5O4 has been synthesised by heating a mixture of titaniumdoped corundum-related α-Fe2O3 with Li2CO3 at 850 C which is ca. 250-350 C lower than temperatures at which the material is normally prepared conventionally. Mössabuer and magnetic measurements imply that the Ti4+ ions substitute for octahedral Fe3+ ions. Interatomic potential calculations support this substitution with the charge balance being maintained by Li+ vacancies.
Spinel-related magnesium-doped Li0. 5Fe2. 5O4 has been synthesised by heating magnesium-substitut... more Spinel-related magnesium-doped Li0. 5Fe2. 5O4 has been synthesised by heating magnesium-substituted corundum-related α-Fe2O3 with Li2CO3 at 600° C which is ca. 600° C lower than the temperature normally used to prepare metal-doped Li0. 5Fe2. 5O4 by conventional sintering methods. Rietveld structure refinement of the X-ray powder diffraction data shows that the Mg2+ ions substitute for Fe3+ ions on the tetrahedral sites whilst the Li+ ions are located on the octahedral sites.
The defect structure of lithiated tin-and titanium-doped α-Fe2O3 has been assessed using interato... more The defect structure of lithiated tin-and titanium-doped α-Fe2O3 has been assessed using interatomic potential calculations. Of the models considered for lithiation, a model in which Li+ occupies an interstitial site balanced by the reduction of Fe3+ to Fe2+ on an Fe3+ site was found to be more favourable than the substitution of Li+ on an Fe3+ octahedral site balanced by an O2− vacancy. Insertion of lithium into the interstitial site between two adjacent M4+ ions was particularly favourable.
Abstract The influence of mechanical alloying and subsequent sintering of a 1: 1 molar mixture of... more Abstract The influence of mechanical alloying and subsequent sintering of a 1: 1 molar mixture of Eu2O3 and Cr2O3 on the formation of EuCrO3 perovskite-related nanocrystalline particles is investigated. Pre-milling the mixture for (75 h) has led to the formation of nanocrystalline EuCrO3 particles (~ 25 nm) at 900oC (12 h). This temperature is~ 300ºC-400ºC lower than those at which the material is prepared via the conventional solid state routes.
There has been considerable interest in the insertion of lithium into iron oxides of the type LiF... more There has been considerable interest in the insertion of lithium into iron oxides of the type LiFeO 2 [1] and [2] and Fe 3 O 4 [3] because of the potential for Li + ion mobility within the rigid three-dimensional host such that the materials might be suitable as electrodes in battery applications. We have recently prepared materials of the type α-Fe 2−x M x O 3 (M=Ti, Sn, Mg) [4] and [5].
Abstract A quaternionic mass defining longitudinal mass () and transverse mass () of a particle i... more Abstract A quaternionic mass defining longitudinal mass () and transverse mass () of a particle is introduced. The longitudinal and transverse masses represent the mass of the particle and matter wave accompanying it, respectively. A massive particle is found to have a bigger longitudinal mass than transverse mass. The particle nature due to the transverse mass of a particle is described by a scalar wave satisfying the Klein-Gordon equation. The transverse mass vector is found to be along the direction of the particle's velocity ().
Abstract—A newly fallen Sudanese meteorite named Al Zarnkh was investigated using room and liquid... more Abstract—A newly fallen Sudanese meteorite named Al Zarnkh was investigated using room and liquid nitrogen temperature Mössbauer measurements, X-ray diffraction (XRD), and electron probe microanalysis (EPMA) in conjunction with energy dispersive X-ray microscopy. The Mössbauer spectra exhibited strong paramagnetic doublets with magnetic sextets. The doublets are assigned to olivine and pyroxene, while the magnetic sextets are assigned to troilite and kamacite.
Chromium and manganese co-substituted spinel magnesioferrites of the composition Mg 1− x Mn x Fe2... more Chromium and manganese co-substituted spinel magnesioferrites of the composition Mg 1− x Mn x Fe2− 2 x Cr 2x O 4 (x= OO, 0.1, 0.2, 0.3, and 0.5) were investigated with X-ray diffraction (XRD), Mössbauer spectroscopy and magnetic measurements. The cation distribution inferred suggests that Mn 2+ and Cr 3+ ions dominantly occupy the A-and Bsites respectively. The gradual decrease of the hyperfine fields and Curie temperatures with increasing x reflects a gradual weakening in the AB exchange interaction.
Abstract The crystal structure and magnetic properties of the spinel system MgFe 2− x Cr x O 4 (w... more Abstract The crystal structure and magnetic properties of the spinel system MgFe 2− x Cr x O 4 (with x= 0, 0.2, 0.4, 0.6, 0.8, 1.0) have been investigated by means of X-ray diffraction (XRD), and Mössbauer spectroscopy. The XRD patterns showed the samples were single-phase cubic spinels. The 295 K Mössbauer spectra of the studied samples showed a continuous collapse of the internal magnetic field for both tetrahedral (A) and octahedral [B] sites with increasing Cr contents.
Abstract Single-phased spinel-related titanium-substituted Li 0.5 Fe 2.5 O 4 has been synthesized... more Abstract Single-phased spinel-related titanium-substituted Li 0.5 Fe 2.5 O 4 has been synthesized by sintering in air a mechanically pre-milled mixture of lithium carbonate, corundum-related iron (III) oxide and the rutile polymorph of titanium (IV) oxide at 700 C (12 h). This temperature is ca. 450–500 C less than the temperatures at which the material is normally prepared by conventional ceramic techniques.
Abstract A structural and Mössbauer study of mechanosynthesized EuCr 1− x Fe x O 3 nanocrystallin... more Abstract A structural and Mössbauer study of mechanosynthesized EuCr 1− x Fe x O 3 nanocrystalline particles (∼ 20–30 nm) is presented. The lattice parameters increase with increasing x-value leading to an increasingly distorted structure. The crystallite sizes range between 20 nm and 30 nm. Magnetic and 57 Fe Mössbauer measurements show the samples with x< 0.7 to be paramagnetic and those with x≥ 0.7 to be partially superparamagnetic at 298 K.
Solid state …, Jan 1, 2002
Tin-and titanium-doped α-Cr2O3 have been prepared by the calcination of precipitates. Rietveld st... more Tin-and titanium-doped α-Cr2O3 have been prepared by the calcination of precipitates. Rietveld structure refinement of the X-ray powder diffraction patterns shows that the dopant metals occupy interstitial sites and partially substitute on octahedral chromium sites in the corundum-related α-Cr2O3 structure. Interatomic potential calculations show that such defects are energetically more favourable than the exclusive substitution of chromium or the occupation by the dopant of interstitial sites in α-Cr2O3 with charge balance being ...
Solid state communications, Jan 1, 2001
A study of the crystallographic structure and magnetic properties of the double perovskites Ba 2 ... more A study of the crystallographic structure and magnetic properties of the double perovskites Ba 2 MnMoO 6 and Sr 2 MnMoO 6 in polycrystalline form has been carried out by means of neutron powder diffraction (NPD) and magnetization measurements. The Rietveld analysis of room temperature data shows that the Mn 2+ and Mo 6+ ions are B-site ordered, i.e. the structure is a NaCl-type ordered double perovskite. Ba 2 MnMoO 6 crystallizes in the cubic space group Fm3m (a = 8.1680(1)) and Sr 2 MnMoO 6 crystallizes in the space group P4 2 /n (a = 7.9575(5), c = 7.9583(9)). Bond valence sum (BVS) calculation revealed that these compounds have the valency pair of {Mn 2+ (3d 5 ;t 3 2g e 2 g ), Mo 6+ (4d 0 )}. The magnetic measurements suggest that these compounds transform to an antiferromagnetic state below 10 K.
Journal of Physics: …, Jan 1, 2010
Single-phased spinel-related Ti 4+ -substituted Li 0.5 Fe 2.5 O 4 has been synthesized by the hea... more Single-phased spinel-related Ti 4+ -substituted Li 0.5 Fe 2.5 O 4 has been synthesized by the heating mixture of hydrothermally prepared Ti 4+ -substituted α-Fe 2 O 3 and Li 2 CO 3 at 850°C (12 h). This temperature is ca. 250-350°C lower than those at which the material is conventionally prepared by the ceramic techniques. X-ray diffraction was used to analyze the evolution of the formation process and, in conjunction with Mössbauer and magnetization measurements, to determine the cation distribution of the resulting ferrite. The results imply that the Ti 4+ ions substitute for Fe 3+ ones at the octahedral (B) sites whilst the excess Li + ions, required for balancing the charge in the spinel-related structure, replace Fe 3+ ions at the tetrahedral (A) sites.
Journal of Solid State Chemistry, Jan 1, 2002
Solid state …, Jan 1, 2002
Chinese Physics Letters, Jan 1, 2010
A generalized continuity equation extending the ordinary continuity equation has been found using... more A generalized continuity equation extending the ordinary continuity equation has been found using quanternions. It is shown to be compatible with Dirac, Schrodinger, Klein-Gordon and diffusion equations. This generalized equation is Lorentz invariant. The transport properties of electrons are found to be governed by Schrodinger-like equation and not by the diffusion equation.
Journal of Physics and Chemistry of …, Jan 1, 2002
The defect structure of lithiated tin-and titanium-doped α-Fe2O3 has been assessed using interato... more The defect structure of lithiated tin-and titanium-doped α-Fe2O3 has been assessed using interatomic potential calculations. Of the models considered for lithiation, a model in which Li+ occupies an interstitial site balanced by the reduction of Fe3+ to Fe2+ on an Fe3+ site was found to be more favourable than the substitution of Li+ on an Fe3+ octahedral site balanced by an O2− vacancy. Insertion of lithium into the interstitial site between two adjacent M4+ ions was particularly favourable. The calculated lattice parameters ...