S. Cottenier

Hyperfine properties at Zr sites of Zr-based compounds. A DFT FP-LAPW and GIPAW study

A. V. Gil Rebaza, A. M. Mudarra Navarro, M. A. Taylor, A. Errico, S. Cottenier
Physica B: Condensed Matter
Volume 657, article number 414757
2023
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Abstract 

We report Density Functional Theory calculations for the atomic positions and the electric-field gradients (EFG) at Zr sites in a series of Zr compounds, with the FP-LAPW and the GIPAW methods. These data are used to obtain a value for the nuclear quadrupole moments of 90Zr and 91Zr, of which the precision and reliability with respect to tabulated values is discussed. An error bar on our suggested values is provided. Good agreement is obtained between the (faster) GIPAW method and (slower yet established) FP-LAPW method, especially when identical atomic positions are imposed. This increases the confidence in GIPAW calculations for electric-field gradient and nuclear quadrupole moment determination.

On the feasibility of online terbium extraction at ISOL@MYRRHA

B. Leenders, A. Aerts, T. E. Cocolios, S. Cottenier, D. Houngbo, L. Popescu
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Volume 541, Page 249-252
2023
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Abstract 

Terbium is an element that has four isotopes with interesting properties for medical applications, 149, 152, 155, 161Tb. These radioisotopes are however far from being sufficiently accessible, thereby hindering the pursuit of research on radiolabelling as well as clinical or preclinical investigations. Their lack of market availability is explained by difficulties in producing these radioisotopes with high purity and specific activity. While 161Tb can be produced using neutron capture in nuclear reactors, for 149, 152, 155Tb, a production route involving the ISOL technique is under study within the Tb-IRMA-V project. The ongoing R&D towards the production and extraction of these isotopes from an ISOL target at the ISOL@MYRRHA facility is reported in this contribution.

How to verify the precision of density-functional-theory implementations via reproducible and universal workflows

E. Bosoni, L. Beal, M. Bercx, P. Blaha, S. Blügel, J. Bröder, M. Callsen, S. Cottenier, A. Degomme, V. Dikan, K. Eimre, E. Flage-Larsen, M. Fornari, A. Garcia, L. Genovese, M. Giantomassi, S. P. Huber, H. Janssen, G. Kastlunger, M. Krack, G. Kresse, T. D. Kühne, K. Lejaeghere, G. K. H. Madsen, M. Marsman, N. Marzari, G. Michalicek, H. Mirhosseini, T. M. A. Müller, G. Petretto, C. J. Pickard, S. Poncé, G.-M. Rignanese, O. Rubel, T. Ruh, M. Sluydts, D. E. P. Vanpoucke, S. Vijay, M. Wolloch, D. Wortmann, A. V. Yakutovich, J. Yu, A. Zadoks, B. Zhu, G. Pizzi
Nature Reviews Physics
2023
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Abstract 

 

Twofold rattling mode-induced ultralow thermal conductivity in vacancy-ordered double perovskite Cs2SnI6

U.-G. Jong, Y.-S.Kim, C.-H. Ri, Y.-H. Kye, C.-J. Pak, S. Cottenier, C.-J. Yu
Chemical Communications
Volume 58, Issue 26, Page 4223-4226
2022
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Abstract 

We report a first-principles study of lattice vibrations and thermal transport in Cs2SnI6, the vacancy-ordered double perovskite. Twofold rattlers of Cs atoms and SnI6 clusters in Cs2SnI6, being different from CsSnI3 with only Cs atom rattlers, largely scatter heat-carrying acoustic phonons strongly coupled with low-lying optical phonons and lower phonon group velocity. Using renormalized phonon dispersions at finite temperatures, we reveal that anharmonicity and twofold rattling modes induce an ultralow thermal conductivity at room temperature.

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
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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
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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
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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
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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
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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.

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