Yann Le Bouar

We demonstrate the use of quantum annealing for the selection of multiple martensite variants in a microstructure with long-range coherency stresses and external mechanical load. The general approach is illustrated for martensites with four different variants based on the minimization of the linear elastic energy. The equilibrium variant distribution is then analyzed under application of tensile and shear strains and for different values of the considered shear and tetragonal contributions of the different martensite variants. The interface orientations between different domains of variants can be explained using the perspective of the elastic energy anisotropy for regular stripe patterns. For random grain orientations, the response to an external elastic strain is weaker and variant changes can be interpreted based on the rotated eigenstrain tensor. Published by the American Physical Society 2024

The surfactant used during a colloidal synthesis is known to control the size and shape of metallic nanoparticles. However, its influence on the nanoparticle (NP) structure is still not well understood. In this study, we show that the surfactant can significantly modify the lattice parameter of a crystalline particle. First, our electron diffraction measurements reveals that NiPt nanoparticles around 4 nm in diameter covered by a mixture of oleylamine and oleic acid (50:50) display a lattice parameter expansion around 2% when compared to the same particles without surfactant. Using high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDX) techniques, we show that this expansion can not be explained by crystal defects, twinning, oxidation, or atoms insertion. Then, using covered NPs in the 4-22 nm size range, we show that the lattice parameter evolves linearly with the inverse of the NP size, as it is expected when a surface stress is present. Finally, the study is extended to pure nickel and pure platinum NPs, with different sizes, coated by different surfactants (oleylamine, trioctylphosphine, polyvinylpyrrolidone). The surfactants induce lattice parameter variations, whose magnitude could be related to the charge transfer between the surfactant and the particle surface.