Category: 2016
| Authors: |
S. A. Rounaghi, H. Eshghi, S. Scudino, A. Vyalikh, D. E. P. Vanpoucke, W. Gruner,
S. Oswald, A. R. Kiani Rashid, M. Samadi Khoshkhoo, U. Scheler and J. Eckert |
| Journal: |
Scientific Reports 6, 33375 (2016) |
| doi: |
10.1038/srep33375 |
| IF(2016): |
4.259 |
| export: |
bibtex |
| pdf: |
<Sci.Rep.> (open access) |
Hexagonal Aluminium nitride (h-AlN) is an important wide-bandgap semiconductor material which is conventionally fabricated by high temperature carbothermal reduction of alumina under toxic ammonia atmosphere. Here we report a simple, low cost and potentially scalable mechanochemical procedure for the green synthesis of nanostructured h-AlN from a powder mixture of Aluminium and melamine precursors. A combination of experimental and theoretical techniques has been employed to provide comprehensive mechanistic insights on the reactivity of melamine, solid state metalorganic interactions and the structural transformation of Al to h-AlN under non-equilibrium ball milling conditions. The results reveal that melamine is adsorbed through the amine groups on the Aluminium surface due to the long-range van der Waals forces. The high energy provided by milling leads to the deammoniation of melamine at the initial stages followed by the polymerization and formation of a carbon nitride network, by the decomposition of the amine groups and, finally, by the subsequent diffusion of nitrogen into the Aluminium structure to form h-AlN
Permanent link to this article: https://dannyvanpoucke.be/paper2016_scirepalnitride-en/
| Authors: |
Arthur De Vos, Kurt Lejaeghere, Danny E. P. Vanpoucke, Jonas J. Joos, Philippe F. Smet, and Karen Hemelsoet |
| Journal: |
Inorg. Chem. 55(5), 2402-2412 (2016) |
| doi: |
10.1021/acs.inorgchem.5b02805 |
| IF(2016): |
4.857 |
| export: |
bibtex |
| pdf: |
<Inorg.Chem> |
 |
| Graphical Abstract: First-principles simulations on zinc gallate solid phosphors (ZGO) containing a chromium dopant and antisite defects (left) rationalize the attractive interactions between the various elements. A large number of antisite pair configurations is investigated and compared with isolated antisite defects. Defect energies point out the stability of the antisite defects in ZGO. Local structural distortions are reported, and charge transfer mechanisms are analyzed based on theoretical density of states (right) and Hirshfeld-I charges. |
Zinc gallate doped with chromium is a recently developed near-infrared emitting persistent phosphor, which is now extensively studied for in vivo bioimaging and security applications. The precise mechanism of this persistent luminescence relies on defects, in particular, on antisite defects and antisite pairs. A theoretical model combining the solid host, the dopant, and/or antisite defects is constructed to elucidate the mutual interactions in these complex materials. Energies of formation as well as dopant, and defect energies are calculated through density-functional theory simulations of large periodic supercells. The calculations support the chromium substitution on the slightly distorted octahedrally coordinated gallium site, and additional energy levels are introduced in the band gap of the host. Antisite pairs are found to be energetically favored over isolated antisites due to significant charge compensation as shown by calculated Hirshfeld-I charges. Significant structural distortions are found around all antisite defects. The local Cr surrounding is mainly distorted due to a ZnGa antisite. The stability analysis reveals that the distance between both antisites dominates the overall stability picture of the material containing the Cr dopant and an antisite pair. The findings are further rationalized using calculated densities of states and Hirshfeld-I charges.
Permanent link to this article: https://dannyvanpoucke.be/paper2016_inorgchemzgodoping-en/
| Authors: |
Danny E. P. Vanpoucke, |
| Journal: |
Developments in Strategic Ceramic Materials:
Ceramic Engineering and Science Proceedings 36(8), 323-334 (2016)
(ICACC 2015 conference proceeding) |
| Editors: |
Waltraud M. Kriven, Jingyang Wang, Dongming Zhu,Thomas Fischer, Soshu Kirihara |
| ISBN: |
978-1-119-21173-0 |
| webpage: |
Wiley-VCH |
| export: |
bibtex |
| pdf: |
<preprint> |
In contemporary materials research, we are able to create and manipulate materials at ever smaller scales: the growth of wires with nanoscale dimensions and the deposition of layers with a thickness of only a few atoms are just two examples that have become common practice. At this small scale, quantum mechanical effects become important, and this is where computational materials research comes into play. Using clever approximations, it is possible to simulate systems with a scale relevant for experiments. The resulting theoretical models provide fundamental insights in the underlying physics and chemistry, essential for advancing modern materials research. As a result, the use of computational experiments is rapidly becoming an important tool in materials research both for predictive modeling of new materials and for gaining fundamental insights in the behavior of existing materials. Computer and lab experiments have complementary limitations and strengths; only by combining them can the deepest fundamental secrets of a material be revealed.
In this paper, we discuss the application of computational materials science for nanowires on semiconductor surfaces, ceramic materials and flexible metal-organic frameworks, and how direct comparison can advance insight in the structure and properties of these materials.
Permanent link to this article: https://dannyvanpoucke.be/paper2016_icacc_gyif-en/
| Authors: |
Danny E. P. Vanpoucke, |
| Journal: |
Developments in Strategic Ceramic Materials:
Ceramic Engineering and Science Proceedings 36(8), 169-177 (2016)
(ICACC 2015 conference proceeding) |
| Editors: |
Waltraud M. Kriven, Jingyang Wang, Dongming Zhu,Thomas Fischer, Soshu Kirihara |
| ISBN: |
978-1-119-21173-0 |
| webpage: |
Wiley-VCH |
| export: |
bibtex |
| pdf: |
<preprint> |
In layered ceramic superconductor architectures, CeO2 buffer layers are known to form micro cracks during the fabrication process. To prevent this crack formation, doping of the CeO2 layer has been suggested. In this theoretical study, the influence of dopants (both tetravalent and aliovalent) on the mechanical and structural properties of CeO2 is investigated by means of density functional theory. Group IVa and IVb dopants show clearly distinct stability, with the former favouring interface and surface doping, while the latter favour uniform bulk doping. This behaviour is linked to the dopant electronic structure. The presence of charge compensating vacancies is shown to complicate the mechanical and structural picture for aliovalent dopants. We find that the vacancies often counteract the dopant modifications of the host material. In contrast, all dopants show an inverse relation between the bulk modulus and thermal expansion coefficient, independent of their valency and the presence of oxygen vacancies. Based on the study of these idealized systems, new dopants are suggested for applications.
Permanent link to this article: https://dannyvanpoucke.be/paper2016_icacc_virtmater-en/
