Etude des sollicitations mécaniques aux interfaces d'un empilement de couches minces - Application à la mesure d'adhérence par la technique de flexion 4 points

Le CEA-LITEN utilise une méthode de mesure d'énergie interfaciale basée sur la technique de flexion 4 points proposée par Charalambides. La valeur de mixité modale doit être connue pour exploiter les résultats de ces essais. Dans cette étude, la simulation par la Méthode des Eléments Finis a été mise en oeuvre pour préciser la mixité modale en fonction des propriétés mécaniques des matériaux et de la configuration des éprouvettes. Dans un second temps, le rôle des contraintes d'élaboration, importantes dans le cas des cellules de SOFC, a été étudié. Ces calculs permettent de dimensionner les éprouvettes

Hole polarons in LaFeO 3 and La1−x_{1−x}Srx_xFeO3−δ_{3−δ} : Stability, trapping, mobility, effect of Sr concentration, and oxygen vacancies

International audienceThe stability, trapping and mobility of electron holes are investigated in lanthanum ferrite LaFeO$_3$ , and in La$_{1−x}$Sr$_x$FeO$_{3−δ}$ ($x$ ≈ 0.1, 0.4 and 0.6) by hybrid-density-functional and densityfunctional-theory $+ U$ calculations. In pure LaFeO$_3$ , the electron hole is more stable under a localized (polaronic) form than under a delocalized form, the energy difference (self-trapping energy) lie between ≈-0.3 and-0.4 eV. This self-trapped hole polaron is not strictly localized on a single Fe atom: instead, it occupies a quantum state made of a 3d orbital of a Fe atom, strongly hybridized with 2$p$ orbitals of four neighboring oxygens. The hole polaron is thus localized on five atoms (among which one single Fe), which can be described as the Fe$^{3+}$ oxidation into Fe$^{4+}$. Electron hole transport results from the combination of onsite reorientations and hoppings, with energy barriers estimated at ≈0.01–0.20 eV and 0.3–0.4 eV, respectively. The aliovalent substitution of lanthanum by strontium in LaFeO$_3$ induces the presence of localized electron holes, preserving the insulating character of La$_{1−x}$Sr$_x$FeO$_3$, regardless of the studied Sr concentration. The formation energy of the oxygen vacancy in La$_{1−x}$Sr$_x$FeO$_3$ (x ≈ 0.1 and 0.4) is estimated at ≈ +0.8 eV. This value is here successfully use to quantify the evolution of defect concentration as a function of the oxygen partial pressur

Stochastic geometrical modeling of SOC electrode microstructures

International audienceDuring the last decades, advances in 3D characterization have been achieved to image the Solid Oxide Cells (SOC) electrode microstructure with a high spatial resolution by using different techniques (FIB-SEM, X-ray tomography…). These techniques enable to study the links between the electrode microstructural and physical properties. However, this approach is time consuming as it requires the manufacturing and the characterization of several cells. An alternative consists in generating representative synthetic microstructures by numerical means in order to increase the amount of data required to establish the correlations linking the electrode microstructure parameters. The proposed talk will then introduce different ways to model and simulate virtual SOC electrode microstructures, of both two-phase electrodes and three-phased composite electrodes, using stochastic geometry. The performance, representativeness and flexibility of such models will be demonstrated and validated on real 3D reconstructions. The author(s) acknowledge(s) the support of the French Agence Nationale de la Recherche (ANR), under grant ANR-18-CE05-0036 (project ECOREVE)

Stochastic geometrical modeling of SOC electrode microstructures

International audienceDuring the last decades, advances in 3D characterization have been achieved to image the Solid Oxide Cells (SOC) electrode microstructure with a high spatial resolution by using different techniques (FIB-SEM, X-ray tomography…). These techniques enable to study the links between the electrode microstructural and physical properties. However, this approach is time consuming as it requires the manufacturing and the characterization of several cells. An alternative consists in generating representative synthetic microstructures by numerical means in order to increase the amount of data required to establish the correlations linking the electrode microstructure parameters. The proposed talk will then introduce different ways to model and simulate virtual SOC electrode microstructures, of both two-phase electrodes and three-phased composite electrodes, using stochastic geometry. The performance, representativeness and flexibility of such models will be demonstrated and validated on real 3D reconstructions. The author(s) acknowledge(s) the support of the French Agence Nationale de la Recherche (ANR), under grant ANR-18-CE05-0036 (project ECOREVE)

Hole polarons in LaFeO 3 and La1−x_{1−x}Srx_xFeO3−δ_{3−δ} : Stability, trapping, mobility, effect of Sr concentration, and oxygen vacancies

International audienceThe stability, trapping and mobility of electron holes are investigated in lanthanum ferrite LaFeO$_3$ , and in La$_{1−x}$Sr$_x$FeO$_{3−δ}$ ($x$ ≈ 0.1, 0.4 and 0.6) by hybrid-density-functional and densityfunctional-theory $+ U$ calculations. In pure LaFeO$_3$ , the electron hole is more stable under a localized (polaronic) form than under a delocalized form, the energy difference (self-trapping energy) lie between ≈-0.3 and-0.4 eV. This self-trapped hole polaron is not strictly localized on a single Fe atom: instead, it occupies a quantum state made of a 3d orbital of a Fe atom, strongly hybridized with 2$p$ orbitals of four neighboring oxygens. The hole polaron is thus localized on five atoms (among which one single Fe), which can be described as the Fe$^{3+}$ oxidation into Fe$^{4+}$. Electron hole transport results from the combination of onsite reorientations and hoppings, with energy barriers estimated at ≈0.01–0.20 eV and 0.3–0.4 eV, respectively. The aliovalent substitution of lanthanum by strontium in LaFeO$_3$ induces the presence of localized electron holes, preserving the insulating character of La$_{1−x}$Sr$_x$FeO$_3$, regardless of the studied Sr concentration. The formation energy of the oxygen vacancy in La$_{1−x}$Sr$_x$FeO$_3$ (x ≈ 0.1 and 0.4) is estimated at ≈ +0.8 eV. This value is here successfully use to quantify the evolution of defect concentration as a function of the oxygen partial pressur

Stochastic geometrical modeling of SOC electrode microstructures

International audienceDuring the last decades, advances in 3D characterization have been achieved to image the Solid Oxide Cells (SOC) electrode microstructure with a high spatial resolution by using different techniques (FIB-SEM, X-ray tomography…). These techniques enable to study the links between the electrode microstructural and physical properties. However, this approach is time consuming as it requires the manufacturing and the characterization of several cells. An alternative consists in generating representative synthetic microstructures by numerical means in order to increase the amount of data required to establish the correlations linking the electrode microstructure parameters. The proposed talk will then introduce different ways to model and simulate virtual SOC electrode microstructures, of both two-phase electrodes and three-phased composite electrodes, using stochastic geometry. The performance, representativeness and flexibility of such models will be demonstrated and validated on real 3D reconstructions. The author(s) acknowledge(s) the support of the French Agence Nationale de la Recherche (ANR), under grant ANR-18-CE05-0036 (project ECOREVE)

Stochastic geometrical modeling of SOC electrode microstructures

International audienceDuring the last decades, advances in 3D characterization have been achieved to image the Solid Oxide Cells (SOC) electrode microstructure with a high spatial resolution by using different techniques (FIB-SEM, X-ray tomography…). These techniques enable to study the links between the electrode microstructural and physical properties. However, this approach is time consuming as it requires the manufacturing and the characterization of several cells. An alternative consists in generating representative synthetic microstructures by numerical means in order to increase the amount of data required to establish the correlations linking the electrode microstructure parameters. The proposed talk will then introduce different ways to model and simulate virtual SOC electrode microstructures, of both two-phase electrodes and three-phased composite electrodes, using stochastic geometry. The performance, representativeness and flexibility of such models will be demonstrated and validated on real 3D reconstructions. The author(s) acknowledge(s) the support of the French Agence Nationale de la Recherche (ANR), under grant ANR-18-CE05-0036 (project ECOREVE)

LaPrNiO4+δ as an innovative oxygen electrode for intermediate temperature solid oxide cells: improving the electrochemical properties by varying the architectural design

International audienc