S. Cottenier

A new ab initio equation of state of hcp-Fe and its implication on the interior structure and mass-radius relations of rocky super-Earths

K. Hakim, A. Rivoldini, T. Van Hoolst, S. Cottenier, J. Jaeken, T. Chust, G. Steinle-Neuman, G. Steinle-Neumann
Icarus
Volume 313, pages 61-78
2018
A1

Abstract 

More than a third of all exoplanets can be classified as super-Earths based on radius (1-2 R-circle plus)) and mass (

Alternative approach to populate and study the Th-229 nuclear clock isomer

M. Verlinde, S. Kraemer, J. Moens, K. Chrysalidis, J.G. Correia, S. Cottenier, H. De Witte, D.V. Fedorov, V.N. Fedosseev, R. Ferrer, L.M. Fraile, S. Geldhof, C.A. Granados, M. Laatiaoui, T.A.L. Lima, P.-C. Lin, V. Manea, B.A. Marsh, I. Moore, L.M.C. Pereira, S. Raeder, P. Van den Bergh, P. Van Druppen, A. Vantomme, E. Verstraelen, U. Wahl, S.G. Wilkins
Physical Review C
100, 2
2019
A1

Abstract 

A new approach to observe the radiative decay of the Th-229 nuclear isomer, and to determine its energy and radiative lifetime, is presented. Situated at a uniquely low excitation energy, this nuclear state might be a key ingredient for the development of a nuclear clock or a nuclear laser and, the search for time variations of fundamental constants like the fine structure constant. The isomer's gamma decay towards the ground state will be studied with a high-resolution vacuum ultraviolet (VUV) spectrometer after its production by the beta decay of Ac-229. The novel production method presents a number of advantages asserting its competitive nature with respect to the commonly used U-233 alpha-decay recoil source. In this paper, a feasibility analysis of this new concept, and an experimental investigation of its key ingredients, using a pure Ac-229 ion beam produced at the ISOLDE radioactive beam facility, is reported.

Structural and electrochemical trends in mixed manganese oxides Na-x(M0.44Mn0.56)O-2 (M = Mn, Fe, Co, Ni) for sodium-ion battery cathode

C.-J. Yu, Y.-C. Pak, C.-H. Kim, J.-S. Kim, K.-C. Ri, K.-H. Ri, S.H. Choe, S. Cottenier
Journal of Power Sources
511, article number: 230395
2021
A1

Abstract 

Developing cost-effective and high performance sodium-ion batteries (SIBs) relies mostly on advanced cathode materials with high electrode voltage, high capacity and fast sodium-ion diffusion. Here, we propose mixed sodium manganese oxides Nax(M0.44Mn0.56)O-2 (M = Mn, Fe, Co, Ni) as improved potential cathode materials for SIBs based on first-principles calculations. Our calculations reveal that these materials have relatively low volume expansion rates below 5%, and are thermodynamically stable. We find that the binding strength between the host and inserted Na atom gradually decreases as increasing the Na content x from 0.11 to 0.67 for each mixed compound, whereas it increases as going Mn -> Fe -> Co -> Ni at each value of Na content. Identifying the intermediate phases during Na insertion/extraction, we find a slight increase of electrode voltage with remarkably higher specific capacities by mixing due to extending the lower limit of Na content. We also investigate the sodium-ion diffusion by identifying plausible pathways , determining the activation barriers and diffusion coefficients , find fast migration within the S-shaped tunnel and moderate one within the small-sized tunnel. Through analysis of density of states, we find that these compounds exhibit half-metallic behaviour, demonstrating an enhancement of metallicity by mixing with higher valent transition metal atoms. Our calculation results show that these mixed compounds can be advanced cathode materials for high performance SIBs.

Metal phosphide CuP2 as a promising thermoelectric material: an insight from a first-principles study

U.-G. Jong, C.-H. Ri, C.-J. Pak, C.-H. Kim, S. Cottenier, C.-J. Yu
New Journal of Chemistry
45, 46, 21569-21576
2021
A1

Abstract 

In the search for better thermoelectric materials, metal phosphides have not been considered to be viable candidates so far, due to their large lattice thermal conductivity. Here we study the thermoelectric properties of metal phosphide CuP2 in the monoclinic phase using first-principles calculations based on self-consistent phonon theory and electron Boltzmann transport theory. Our lattice dynamics calculations reveal that CuP2 exhibits Cu-dimer rattling modes, which strongly scatter the heat-carrying acoustic and low-lying optical phonons, resulting in an unusually low lattice thermal conductivity below 3.6 W m(-1) K-1, being about a half of the conventional thermoelectrics GeTe. We predict Seebeck coefficients, the value of which at 300 K is in good accordance with the experiment, and power factors that are superior to the conventional thermoelectrics GeTe, possibly due to flat- and dispersive-band structures with high orbital degeneracy. Finally, we assess its thermoelectric performance by evaluating the figure of merit ZT, finding that upon p-type doping ZT can reach over 1.3 at a high temperature of 700 K by optimizing the hole concentration. Our results highlight the potential of using metal phosphide CuP2 as a promising material for thermoelectric applications with practical performance and low cost.

The electric field gradient as a signature of the binding and the local structure of adatoms on graphene

A.S. Fenta, C.O.Amorim, J.N.Goncalves, N. Fortunato, M.B. Barbosa, S. Cottenier, J.G. Correia, L.M.C. Pereira, V.S. Amaral
Applied Physics A-Materials Science & Processing
127, 8, artice number: 573
2021
A1

Abstract 

We examined the interaction between adatoms and graphene for Ag, Cd, In and Hg by density functional theory. We establish a relation between the binding energy and the electric-field gradient tensor (EFG) for each atom, which indicates that hyperfine interactions can be used to probe the binding and stability of adatoms on graphene. The EFG is also shown to be a fingerprint for the local configuration, even at the sub-Angstrom scale. This work demonstrates how suitable hyperfine methods, such as perturbed angular correlation spectroscopy, can be used to experimentally unravel details of atomic adsorption on graphene, and by extension on two-dimensional materials in general.

Reactivity of Single Transition Metal Atoms on a Hydroxylated Amorphous Silica Surface: A Periodic Conceptual DFT Investigation

X. Deraet, J. Turek, M. Alonso, F. Tielens, S. Cottenier, P.W. Ayers, B.M. Weckhuysen, F. De Proft
Chemistry - A European Journal
27, 19 , 6050-6063
2021
A1

Abstract 

The drive to develop maximal atom-efficient catalysts coupled to the continuous striving for more sustainable reactions has led to an ever-increasing interest in single-atom catalysis. Based on a periodic conceptual density functional theory (cDFT) approach, fundamental insights into the reactivity and adsorption of single late transition metal atoms supported on a fully hydroxylated amorphous silica surface have been acquired. In particular, this investigation revealed that the influence of van der Waals dispersion forces is especially significant for a silver (98 %) or gold (78 %) atom, whereas the oxophilicity of the Group 8-10 transition metals plays a major role in the interaction strength of these atoms on the irreducible SiO2 support. The adsorption energies for the less-electronegative row 4 elements (Fe, Co, Ni) ranged from -1.40 to -1.92 eV, whereas for the heavier row 5 and 6 metals, with the exception of Pd, these values are between -2.20 and -2.92 eV. The deviating behavior of Pd can be attributed to a fully filled d-shell and, hence, the absence of the hybridization effects. Through a systematic analysis of cDFT descriptors determined by using three different theoretical schemes, the Fermi weighted density of states approach was identified as the most suitable for describing the reactivity of the studied systems. The main advantage of this scheme is the fact that it is not influenced by fictitious Coulomb interactions between successive, charged reciprocal cells. Moreover, the contribution of the energy levels to the reactivity is simultaneously scaled based on their position relative to the Fermi level. Finally, the obtained Fermi weighted density of states reactivity trends show a good agreement with the chemical characteristics of the investigated metal atoms as well as the experimental data.

Hg adatoms on graphene: A first-principles study

A.S. Fenta, C.O. Amorim, J.N. Goncalvez, N. Fortunato, M.B. Barbosa, J.P. Araujo, M. Houssa, S. Cottenier, M.J. Van Bael, J.G. Correia, V.S. Amaral, L.M.C. Pereira
Journal of Physics-Materials
Volume 4 Issue1
2021
A1

Abstract 

The interest in understanding the interaction between graphene and atoms that are adsorbed on its surface (adatoms) spans a wide range of research fields and applications, for example, to controllably change the properties of graphene in electronic devices or to detect those changes in graphene-based sensors. We present a density functional theory study of the interaction between graphene and Hg adatoms. Binding energy, electronic structure and electric field gradient (EFG) were calculated for various high-symmetry atomic configurations, from isolated adatoms to a continuous Hg monolayer. Hg as isolated adatom was found to be the most stable configuration, with a binding energy of 188 meV. Whereas isolated adatoms have a minor effect on the electronic structure of graphene (small acceptor effect), Hg monolayer configurations induce a metallic state, with the Fermi level moving well above the Dirac point (donor behavior). Based on the EFG calculated for the various configurations, we discuss how hyperfine techniques (perturbed angular correlation spectroscopy, in particular) can be used to experimentally study Hg adsorption on graphene.

Race against the Machine: can deep learning recognize microstructures as well as the trained human eye?

M. Larmuseau, M. Sluydts, K. Theuwissen, L. Duprez, T. Dhaene, S. Cottenier
Scripta Materialia
193, 33-37
2021
A1

Abstract 

The promising results of deep learning in image recognition suggest a huge potential for microscopic analyses in materials science. One major challenge for its adoption in the study of materials is the limited number of images that are available to train models on. Herein, we present a methodology to create accurate image recognition models with small datasets. By explicitly taking into account the magnification and by introducing appropriate transformations, we incorporate as many insights from material science in the model as possible. This allows for a highly data-efficient training of complex deep learning models. Our results indicate that a model trained with the presented methodology is able to outperform human experts.

Compact representations of microstructure images using triplet networks

M. Larmuseau, M. Sluydts, K. Theuwissen, L. Duprez, T. Dhaene, S. Cottenier
npj Computational Materials
6, 156
2020
A1

Abstract 

The microstructure of a material, typically characterized through a set of microscopy images of two-dimensional cross-sections, is a valuable source of information about the material and its properties. Every pixel of the image is a degree of freedom causing the dimensionality of the information space to be extremely high. This makes it difficult to recognize and extract all relevant information from the images. Human experts circumvent this by manually creating a lower-dimensional representation of the microstructure. However, the question of how a microstructure image can be best represented remains open. From the field of deep learning, we present triplet networks as a method to build highly compact representations of the microstructure, condensing the relevant information into a much smaller number of dimensions. We demonstrate that these representations can be created even with a limited amount of example images, and that they are able to distinguish between visually very similar microstructures. We discuss the interpretability and generalization of the representations. Having compact microstructure representations, it becomes easier to establish processing–structure–property links that are key to rational materials design.

Open Access version available at UGent repository

Pages

Subscribe to RSS - S. Cottenier