ORCID Profile
0000-0002-9292-1223
Current Organisation
University of South Australia
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Publisher: Elsevier BV
Date: 02-2010
Publisher: Elsevier BV
Date: 04-2017
Publisher: Elsevier BV
Date: 2015
Publisher: Elsevier BV
Date: 04-2020
Publisher: InTech
Date: 28-02-2011
DOI: 10.5772/14892
Publisher: Springer Science and Business Media LLC
Date: 10-2009
Publisher: Elsevier BV
Date: 06-2019
Publisher: Elsevier BV
Date: 07-2022
Publisher: American Association for the Advancement of Science (AAAS)
Date: 04-06-2021
Abstract: Spinodal decomposition is discovered to be an effective way to strengthen magnesium alloy.
Publisher: MDPI AG
Date: 16-02-2022
Abstract: First principles calculations were carried out on six different grain boundaries with complex, non-symmetrical, crystallography’s. Solute species (Gd and Zn) were placed in multiple locations to investigate their effect on the boundary energetics. The grain boundaries were found to have an intrinsic grain boundary energy, and this energy was not markedly affected by the solute concentration at the boundary. However, the work of separation (WSEP) was very sensitive to grain boundary chemistry. Boundaries of higher disorder were found to be more sensitive to boundary chemistry and showed higher values of WSEP and in the case of Gd, were more sensitive to solute concentration at the boundary. No correlation between the boundary behaviour and crystallography could be found, apart from the over-riding conclusion that all six boundaries showed markedly different behaviours, and the effect of solute on each were unique.
Publisher: Elsevier BV
Date: 06-2017
Publisher: Elsevier BV
Date: 12-2016
Publisher: Elsevier BV
Date: 11-2017
Publisher: American Physical Society (APS)
Date: 02-11-2010
Publisher: American Physical Society (APS)
Date: 14-03-2017
Publisher: AIP Publishing
Date: 15-12-2008
DOI: 10.1063/1.3042222
Abstract: We investigate theoretically ferroelastic domain fractions in a heteroepitaxial bilayer consisting of (001) tetragonal PbZrxTi1−xO3 and (001) rhombohedral PbZr1−xTixO3 on a thick (001) passive substrate as a function of the lattice misfit strain between layers and the substrate. By considering the self-strain in each layer and the indirect elastic interaction between the layers, we provide a numerical analysis of the relative domain fractions in the tetragonal layer of a (001)PbZr0.2Ti0.8O3/(001)PbZr0.8Ti0.2O3 and (001)PbZr0.4Ti0.6O3/(001)PbZr0.6Ti0.4O3 bilayer structure as a function of the tetragonal layer thickness on (001)LaAlO3, (001)SrTiO3, and (001) MgO. It is found that the elastic coupling between the tetragonal and rhombohedral layers leads to an excess elastic energy in the tetragonal layer, resulting in a two to three times increase in the ferroelastic domain volume fraction of the tetragonal layer compared to single-layer films of similar thickness. These results show alternate ways of engineering ferroelastic domain structures in ferroelectric thin films.
Publisher: Mineralogical Society of America
Date: 05-2023
DOI: 10.2138/AM-2022-8415
Abstract: Arsenian pyrite is known to have a strong association with gold in most auriferous refractory deposits, and thus understanding the chemical speciation of arsenic in localized environments in arsenian pyrite provides an important basis for determining its reactivity and mobility. However, arsenic is fast-oxidizing among elements in the Fe-As-S system and hence it may exist in various chemical states, which renders it difficult to establish arsenic nature under pristine conditions, particularly in arsenian pyrite. Herein, arsenian pyrite s les were analyzed on a synchrotron soft X-ray spectroscopy beamline under ultrahigh vacuum conditions, and As-3d as well as S-2p spectra were collected. A comparison between the spectrum of bulk As-3d in the s les with its bulk counterpart in arsenopyrite revealed a 0.6 eV shift toward lower binding energies. This observation was similar to loellingite (FeAs2), where the binding energy shift was attributed to high electron density on As of the As-As dimer. Formation of As clusters resulting in comparable binding energy shifts was also proposed from the spectroscopic studies. The experiments were complemented by a series of first-principles calculations simulating four experimentally observed pyrite surfaces where surficial S atoms were randomly substituted by As. As such, six arsenian pyrite crystal surfaces were modeled, two of which constituted surficial As clusters replacing both S and Fe atoms. The surfaces were geometrically optimized, and surface energies were calculated along with the corresponding electronic structure providing a detailed distribution of partial charges for surficial atoms obtained from Löwdin population analysis. The calculated partial charges of atoms located at the surface arsenian pyrite indicated that while the electron density on the As atom of As-S dimers in arsenian pyrite is less negative than the As in bulk arsenopyrite, it is more negative for the As atom of As-As dimers, which were only seen in the surficial As clusters. This validated the description of As presence in arsenian pyrite as local clusters inducing localized lattice strain due to increased bond distances. Our findings offer a good background for future studies into the reactive sites in arsenian pyrite and how that compares with associated minerals, arsenopyrite, and pyrite.
Publisher: Wiley
Date: 18-03-2021
DOI: 10.1002/POL.20210095
Publisher: Elsevier BV
Date: 05-2013
Publisher: American Physical Society (APS)
Date: 19-09-2011
Publisher: AIP Publishing
Date: 22-12-2020
DOI: 10.1063/5.0031505
Abstract: First-principles calculations within the local density approximation were carried out to explain the ground state and electronic properties of a vacuum/PbTiO3/SrTiO3/PbTiO3/SrRuO3 multilayer in a monodomain phase. Open-circuit boundary conditions were assumed, considering the electric displacement field, D, as the fundamental electrical variable. The direction and the magnitude of D can be monitored by proper treatment of the PbO surface layer, introducing external fractional charges Q in the surface atomic layers by means of virtual crystal approximation. Different excess or deficit surface charges (from Q=±0.05 to Q=±0.15) were considered, corresponding to small values of the polarization (up to ±0.16C/m2) in both directions. The layer-by-layer electric polarization, tetragonality, and the profile of the electrostatic potential were computed, as well as the projected density of states, as a function of electric displacement field. The magnitude of D is preserved across the dielectric layers, which translates into a polarization of the SrTiO3 spacer layer. The tetragonality of the two PbTiO3 layers is different, in good agreement with experimental x-ray diffraction techniques, with the layer closer to the free surface exhibiting a smaller value. This is attributed to the interplay with surface effects that tend to contract the material in order to make the remaining bonds stronger. Our calculations show how the final structure in this complex oxide heterostructure comes from a delicate balance between electrical, mechanical, and chemical boundary conditions.
Publisher: Elsevier BV
Date: 10-2015
Publisher: Wiley
Date: 02-06-2010
Publisher: American Chemical Society (ACS)
Date: 06-07-2022
Publisher: Elsevier BV
Date: 10-2018
Publisher: Wiley
Date: 03-09-2009
Publisher: MDPI AG
Date: 23-11-2020
DOI: 10.3390/MET10111561
Abstract: Two groups of martensitic alloys were examined for changes induced by deep cryogenic treatment (DCT). The first group was a range of binary and ternary compositions with 0.6 wt % carbon, and the second group was a commercial AISI D2 tool steel. X-ray diffraction showed that DCT made two changes to the microstructure: retained austenite was transformed to martensite, and the dislocation density of the martensite was increased. This increase in dislocation density was consistent for all alloys, including those that did not undergo phase transformation during DCT. It is suggested that the increase in dislocation density may be caused by local differences in thermal expansion within the heterogeneous martensitic structure. Then, s les were tempered, and the cementite size distribution was examined using small angle neutron scattering (SANS) and atom probe tomography. First principles calculations confirmed that all magnetic scattering originated in cementite and not carbon clusters. Quantitative SANS analysis showed a measurable change in cementite size distribution for all alloys as a result of prior DCT. It is proposed that the increase in dislocation density that results from DCT modifies the cementite precipitation through enhanced diffusion rates and increased cementite nucleation sites.
Publisher: Springer Science and Business Media LLC
Date: 08-07-2021
DOI: 10.1038/S41598-021-93703-W
Abstract: Although magnesium alloys are lightweight, recyclable and relatively cheap, they suffer from poor ductility. This can be improved by the addition of rare earth (RE) elements, and this is now a well-established criterion for wrought alloy design. It is notable that this behavior is largely restricted to the lanthanides, but no hypothesis is yet available to explain why other elements do not have the same effect. To answer this question, ab initio simulations of crystallographically complex boundaries have been undertaken to examine the electronic origin of the RE effect. While the electronic structure provided strong bonding between the RE elements and their Mg surroundings, local disruption in atomic arrangement at the grain boundaries was found to modify this effect. This work shows quantifiable changes in electronic structure of solutes resulting from grain boundary crystallography, and is suggested to be a contributing factor to the RE texture effect.
Publisher: Springer Science and Business Media LLC
Date: 21-10-2016
DOI: 10.1038/NPJCOMPUMATS.2016.29
Abstract: The vibrational spectra of a series of MgZnCa amorphous alloys were computed using density functional theory and implementing the small displacement method. The atomic structures of the alloys were obtained by ab initio molecular dynamics simulations. The vibrational thermodynamic properties were calculated as a function of temperature and, in particular, the specific heat at low temperature was approximated by temperature cubed based on the Debye model. We computed the contribution of Mg vibrations to the specific heat and investigated the softening of Mg phonon spectra, where the maximum allowed vibrational frequency is lowered and highly collective diffusion processes are promoted. The statistical correlation between the reported critical casting thickness of the alloys and softening of Mg phonons was obtained. Similar calculations were performed for two distinctively different amorphous ZrTiCuAl alloys with large and small reported critical casting thickness, respectively. The findings were consistent with those of the MgZnCa alloys.
Publisher: Wiley
Date: 06-2023
Abstract: Smart materials that are energy efficient and take up less space are crucial in the development of new technologies. Electrochromic polymers (ECPs) are one such class of materials that actively change their optical behavior in both visible and infrared parts of the electromagnetic spectrum. They show promise in a wide range of applications, from active camouflage to smart displays/windows. The full capabilities of ECPs are still yet to be explored, for while their electrochromic properties are well established, their Infrared (IR) modulation is less reported on. This study addresses the potential of ECPs in active IR modulating devices by optimization of Vapor Phase Polymerized poly(3,4‐ethylenedioxythiophene) (PEDOT) thin films via the substitution of its dopant anion. Dynamic ranges denoting emissivity changes between reduced and oxidized states of PEDOT are found across dopants of tosylate, bromide, sulfate, chloride, perchlorate, and nitrate. Relative to the emissivity of reduced (neutral) PEDOT, a range of ±15% is achieved from the doped PEDOT films, and a maximum dynamic range of 0.11 across a 34% change is recorded for PEDOT doped with perchlorate.
No related grants have been discovered for Reza Mahjoub.