arXiv subjects

Pierre Hirel

Publications and source records attributed to Pierre Hirel.

6 recordsLinked to original sources

arXiv2026

Ferroelectric switching at edge dislocations in BaTiO$_3$ modelled at the atomic scale

Ferroelectric switching governs the functional properties of ferroelectric perovskites. It is widely accepted that this switching depends on domain nucleation and pinning and that these processes can be controlled by the defect structure. However, an atomistic picture of the influence of one important class of defects - dislocations on ferroelectric switching is missing. This is an important gap in knowledge as dislocations cannot be avoided at interfaces and can also be engineered by plastic deformation at high temperatures. Using atomistic simulations, we show how the cores of $\langle100\rangle$ edge dislocations in BaTiO$_3$ can either act as nucleation centers for ferroelectric switching or pin walls depending on the direction of the applied field. The coupling between electric field and polarization is strongest when the field is applied parallel to the Burgers vector of the dislocation.

cond-mat.mtrl-sci↗

arXiv2025

Coupled electromigration-nanoindentation study on dislocation nucleation in SrTiO3

Modern functional oxides are mainly engineered by doping, essentially by tuning the defect chemistry. Recent studies suggest that dislocations offer a new perspective for enhancing the mechanical and physical properties of ceramic oxides. This raises the question regarding the interaction between dislocations and point defects in ceramics. Here, we report the impact of defect chemistry on the mechanical response of single-crystal strontium titanate, a prototype perovskite oxide. We demonstrate that electric field-induced stoichiometry polarization alters the defect chemistry, primarily by tuning oxygen vacancies, resulting in a distinct difference in the maximum shear stresses for dislocation nucleation, as experimentally observed and corroborated by molecular dynamic simulation. The impact of indenter tip size and geometry on the dislocation nucleation behavior in samples with different point defect concentrations in ceramics is further elucidated. Similar to the electromigration findings, acceptor-doped SrTiO3 tends to promote dislocation nucleation due to the abundance of oxygen vacancies. These findings shed new light on the interaction between dislocations and point defects in oxides. They may pave the road for assessing the stability of the next-generation functional ceramics engineered by dislocations.

cond-mat.mtrl-sci↗

arXiv2025

Dislocations and plasticity of KTaO$_3$ perovskite modeled with a new interatomic potential

Potassium tantalate KTaO3 is a cubic, paraelectric perovskite ceramic that exhibits surprising ductility at room temperature as most recently reported. Much like strontium titanate (SrTiO3), plastic deformation is accommodated by dislocations gliding in {110} planes. In this work we propose a new interatomic potential for KTaO3, and apply it to model dislocations with <110> Burgers vector. We demonstrate that dislocations dissociate, and finely characterize their core structure and Peierls potential. Dislocations of edge character can carry a positive or negative electric charge, but we show that charge-neutral configurations are energetically more favorable. We also perform high-resolution electron microscopy to validate our simulation methodology. Comparing our results with other ductile perovskites, we confirm KTaO3 to be ductile, but stiffer than SrTiO3.

cond-mat.mtrl-sci↗

arXiv2022

Pinning of domain walls by strontium layer in BaTiO3 perovskite: an atomic-scale study

We use atomistic simulations to study the interactions between two-dimensional domain walls and Sr inclusions in the prototypical ferroelectric BaTiO$_3$. Based on nudged elastic band calculations we predict that the energy barrier for domain wall movement increases in the vicinity of small planar Sr inclusions which may act as pinning centers. We link this observation to the local increase in polarization by larger oxygen off-centering and validate our predictions by molecular dynamics simulations of field-driven domain walls at finite temperatures.

cond-mat.mtrl-sci↗

arXiv2015

Effects of sublattice symmetry and frustration on ionic transport in garnet solid electrolytes

We use rigorous group-theoretic techniques and molecular dynamics to investigate the connection between structural symmetry and ionic conductivity in the garnet family of solid Li-ion electrolytes. We identify new ordered phases and order-disorder phase transitions that are relevant for conductivity optimization. Ionic transport in this materials family is controlled by the frustration of the Li sublattice caused by incommensurability with the host structure at non-integer Li concentrations, while ordered phases explain regions of sharply lower conductivity. Disorder is therefore predicted to be optimal for ionic transport in this and other conductor families with strong Li interaction.

cond-mat.mtrl-sci↗

arXiv2007

Effects of temperature and surface step on the incipient plasticity in strained aluminium studied by atomistic simulations

Atomistic simulations using an EAM potential are carried out to investigate the first stages of plasticity in aluminum slabs, in particular the effect of both temperature and step geometry on the nucleation of dislocations from surface steps. Temperature is shown to significantly reduce the elastic limit, and to activate the nucleation of dislocation half-loops. Twinning occurs by successive nucleations in adjacent glide planes. The presence of a kinked step is shown to have no influence on the nucleation mechanisms.

cond-mat.other↗