Laboratoire Léon Brillouin

UMR12 CEA-CNRS

Bât. 563 CEA Saclay

91191 Gif sur Yvette Cedex

France

llb-sec@cea.fr

PhD subjects

5 sujets IRAMIS//LLB

Dernière mise à jour : 18-03-2019


• Radiation-matter interactions

• Soft matter and complex fluids

• Solid state physics, surfaces and interfaces

 

Quantum fragmentation in frustrated magnets

SL-DRF-19-0538

Research field : Radiation-matter interactions
Location :

Laboratoire Léon Brillouin

Groupe 3 Axes

Saclay

Contact :

SYLVAIN PETIT

ELSA LHOTEL

Starting date : 01-10-2018

Contact :

SYLVAIN PETIT

CEA - DRF/IRAMIS

01 69 08 60 39

Thesis supervisor :

ELSA LHOTEL

CNRS - Insitut Néel

04 76 88 12 63

Personal web page : http://iramis.cea.fr/Phocea/Membres/Annuaire/index.php?uid=spetit

Laboratory link : http://www-llb.cea.fr/

Magnetic frustration is one of the modern routes in condensed matter physics leading to the discovery of new states of matter. The “spin ice” and more generally, the “Coulomb phases” are celebrated examples of this physics. In contrast with classical magnetically ordered phases, these states remain disordered down to the lowest temperatures, yet form a correlated paramagnet with specific spin-spin correlations. In this context, a new concept has been recently proposed, called “magnetic fragmentation” [PRX 4, 011007 (2014)]. This is an original state where the magnetic moment fragments into two sub-fragments: one of them forms an antiferromagnetic phase with a reduced ordered moment, while the other keeps fluctuating and forms a Coulomb phase.



In combining magnetization measurements, elastic and inelastic neutron scattering experiments, we have shown that the pyrochlore compound Nd2Zr2O7 could be a realization of this theory [1,2], even if experimental evidences suggest that still not understood quantum phenomena are at play.



This thesis work aims at understanding the origin of fragmentation in this system. We especially plan to determine its stability range by studying doped samples. Actually, replacing part of the Zirconium (Zr) by Titanium (Ti), or Neodymium (Nd) by Lanthanum (La), magnetic interactions can be modified. Varying the substitution, we will explore the phase diagram and probe the possible existence of a quantum critical point predicted by theory. The complementarity between macroscopic and neutron scattering measurements is one of the key points to determine the quantum Hamiltonian and beyond, understand the microscopic mechanisms of magnetic fragmentation, along with the nature of the spin dynamics that emerge from this peculiar ground state.



The thesis work will take place in France both at the Institut Néel (Grenoble) and at LLB (Saclay). It consists in measuring both the magnetization and specific heat down to base temperature (100 mK) (Institut Néel) and to finely determine the magnetic structures as well as the spin excitations spectrum by the different neutron techniques. The latter will be carried out at LLB (Saclay) and at ILL (Grenoble). A large part of the data analysis will be based on numerical simulation tools. Most of them exist today but may be further developed.

“Smart” Composite Membranes for Lithium-Metal-Polymer Batteries.

SL-DRF-19-0850

Research field : Soft matter and complex fluids
Location :

Laboratoire Léon Brillouin

Groupe Biologie et Systèmes Désordonnés

Saclay

Contact :

Quentin BERROD

Jean-Marc ZANOTTI

Starting date : 01-10-2019

Contact :

Quentin BERROD

CNRS - DRF/INAC/SyMMES/STEP

(+33)(0)438786425

Thesis supervisor :

Jean-Marc ZANOTTI

CEA - DRF/IRAMIS/LLB/GBSD

+33(0)476207582

Personal web page : http://iramis.cea.fr/Pisp/jean-marc.zanotti/

Laboratory link : http://www-llb.cea.fr/

More : https://icr-amu.cnrs.fr/

At the present stage, in the electrochemical device landscape, solid-state polymer lithium batteries offer an interesting compromise in terms of specific stored energy and power. Nevertheless, to achieve practical conduction they need to operate at relatively high temperature (80°C). This condition significantly hampers the performances of the system. The top-one priority of manufacturers in the field is to decrease the working temperature of their products. This project proposes a fundamental science approach targeting the delivery of a “proof of concept” polymer based lithium metal battery working at room temperature.



This ambitious goal will be achieved by taking advantage of i) the confinement of the electrolyte within composite Carbon NanoTube (CNT) membranes (Gibbs-Thomson effect), ii) one-dimensional (1D) ionic conductivity, and iii) the use of low molecular mass PEO (high mobility). The reduction of dimensionality will be obtained by using the quasi-perfect 1D topology offered by vertically aligned CNT forests.



The suppression of the electrical conductivity of the CNT is a critical aspect to use 1D CNT membranes as battery separators. Short PEO chains will be therefore grafted onto the CNT caps to achieve at once good ionic conduction at the CNT pore entrance and ensure electrical insulation of the CNT/electrode contact. Depending on the physico-chemical conditions on one side of the membrane (pH, temperature…), one can expect drastic changes in the conformation of the CNT-tips-grafted-polymer layer: from extended to mushroom conformation. Therefore, beyond the present project, such smart membranes could be turned into “nano-valves”, able to gate the flow between different media.

Single-ion hybrid polymer electrolytes for Li-metal battery

SL-DRF-19-0554

Research field : Soft matter and complex fluids
Location :

Laboratoire Léon Brillouin

Groupe de Diffusion Neutron Petits Angles

Saclay

Contact :

Jacques JESTIN

Starting date : 01-10-2019

Contact :

Jacques JESTIN

CNRS - LLB01/Laboratoire de Diffusion Neutronique

0661476825

Thesis supervisor :

Jacques JESTIN

CNRS - LLB01/Laboratoire de Diffusion Neutronique

0661476825

Lithium metal polymer" Batteries: towards operation at ambient temperature

SL-DRF-19-0563

Research field : Soft matter and complex fluids
Location :

Laboratoire Léon Brillouin

Groupe Biologie et Systèmes Désordonnés

Saclay

Contact :

Jean-Marc ZANOTTI

Starting date : 01-10-2019

Contact :

Jean-Marc ZANOTTI

CEA - DRF/IRAMIS/LLB/GBSD

+33(0)476207582

Thesis supervisor :

Jean-Marc ZANOTTI

CEA - DRF/IRAMIS/LLB/GBSD

+33(0)476207582

Personal web page : http://iramis.cea.fr/Pisp/jean-marc.zanotti/

Laboratory link : http://www-llb.cea.fr/

More : http://liten.cea.fr/cea-tech/liten/Pages/Accueil.aspx

This PhD subject proposes an original way to allow the use of "lithium metal polymer" batteries at room temperature. This objective will be achieved by combining three effects:

i) The nanometric confinement of the electrolyte in membranes based on vertically aligned Carbon NanoTubes (VA-CNT),

ii) The use of low molecular weight polymer (here Poly(Ethylene Oxide (PEO))

iii) One-dimensional ionic conduction.



The conduction of the CNT confined Lithium will be driven by two characteristic distances: the pore diameter (1-4 nm) and the total VA-CNT length (from 10 to 500 micrometers). Rational modeling of the transport properties over distances differing by orders of magnitude naturally calls for a multiscale approach.

Therefore, as for its fundamental Science aspect, the primary goal is to develop an experimental multi-scale approach to bridge the broad time and spatial scales (eight orders of magnitude) relevant to the high-mobility-in-tight-1D-spaces we are seeking.

The applied research fold of the study is to prove the validity of the concept.

Linear magnetoelectric and multiferroic properties in A4A’2O9 antiferromagnets

SL-DRF-19-0539

Research field : Solid state physics, surfaces and interfaces
Location :

Laboratoire Léon Brillouin

Groupe Diffraction Poudres

Saclay

Contact :

Françoise Damay

Starting date : 01-10-2019

Contact :

Françoise Damay

CEA - DRF/IRAMIS/LLB/GDP

0169084954

Thesis supervisor :

Françoise Damay

CEA - DRF/IRAMIS/LLB/GDP

0169084954

Personal web page : http://iramis.cea.fr/Pisp/francoise.damay/

Laboratory link : http://www-llb.cea.fr/

The general context of this PhD work is the search for new multiferroics, compounds in which magnetisation and electric polarization are coupled, allowing for instance a magnetic field to modify the polarization, of an electric field to change magnetization.



In the proposed work, a new family of promising multiferroics will be investigated, namely niobiates and tantalates of general formula A4A'O9 with A a divalent transition metal. In work published in 2018, it was shown that in particular Fe4Ta2O9 exhibits both multiferroic and linear magneto-electric properties, depending on the temperature range. This suggests different spin/charge couplings that remain to be explored and understood. Experimental techniques will be devoted to the understanding of the relations ships between crystal and magnetic structures and physical properties: for the most part, the student will deal with magnetization, dielectric constant and polarization measurements, coupled with X-ray and neutron diffraction experiments versus temperature.

 

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