Sonia Buffière

Bio: Sonia Buffière is an academic researcher from University of Bordeaux. The author has contributed to research in topics: Sintering & Electrochromism. The author has an hindex of 6, co-authored 16 publications receiving 118 citations. Previous affiliations of Sonia Buffière include Centre national de la recherche scientifique.

Anisotropic Metal Deposition on TiO2 Particles by Electric-Field-Induced Charge Separation

Abstract: Deposition of metals on TiO2 semiconductor particles (M-TiO2) results in hybrid Janus objects combining the properties of both materials. One of the techniques proposed to generate Janus particles is bipolar electrochemistry (BPE). The concept can be applied in a straightforward way for the site-selective modification of conducting particles, but is much less obvious to use for semiconductors. Herein we report the bulk synthesis of anisotropic M-TiO2 particles based on the synergy of BPE and photochemistry, allowing the intrinsic limitations, when they are used separately, to be overcome. When applying electric fields during irradiation, electrons and holes can be efficiently separated, thus breaking the symmetry of particles by modifying them selectively and in a wireless way on one side with either gold or platinum. Such hybrid materials are an important first step towards high-performance designer catalyst particles, for example for photosplitting of water.

From core–shell BaTiO3@MgO to nanostructured low dielectric loss ceramics by spark plasma sintering

Abstract: We report a quite general way to design materials with tailored properties by combining thermolysis and fast sintering approaches. Submicrometric-sized BaTiO3 particles have been directly coated in a continuous nanocrystalline MgO shell through a thermal decomposition process. The electron microscopy study has evidenced a shell composed of randomly oriented MgO nanocrystallites. The final nanostructured composite, made of sub-micrometric MgO and BaTiO3 grains uniformly distributed, is obtained in situ during the SPS process. Such a rearrangement can be explained by the initial core–shell architecture, the weak cohesion of the MgO nanocrystallites and their soft plastic behavior under SPS conditions. The composite effect leads to significant modifications in both the dielectric properties and Curie–Weiss parameters compared to uncoated BaTiO3, especially a decrease and thermal stabilization of both the permittivity and the dielectric losses. We ascribe such changes to the stress generated during SPS through the extended interfaces between the two components.

The versatile Co2+/Co3+ oxidation states in cobalt alumina spinel: how to design strong blue nanometric pigments for color electrophoretic display

Abstract: Blue cobalt inorganic pigments with spinel-type structure have been revisited in order to understand the origin of blackening at low temperatures and to design strong blue nanosized materials. Starting from a sol–gel process, the so-called Pechini route, the correlation between the structural features (inversion rate, Co over-stoichiometry, Co valence states) of the spinel network and its thermal history under air up to high temperatures (T = 1400 °C) allows concluding that the stabilization of CoIII in octahedral sites is at the origin of the blackening of the pigment annealed at low and medium temperatures. EELS coupled with TEM analyses (occurrence of multiple phases with various Al/Co atomic ratios) lead to us to conclude definitively about the variation of Co valence states. A top-down (mechanical grinding) and a bottom-up approach lead to the definition of a synthesis route (co-precipitation in basic medium followed by annealing at medium temperatures under Ar) allowing the design of strong blue pure nano-sized pigments to be incorporated in inks. Hybrid blue positively charged particles were mixed with white negatively charged particles to formulate dual-colour inks. A dual-colour display was filled with the as-prepared inks and tested under ±150 V.

The Interplay between Surface Plasmon Resonance and Switching Properties in Gold@Spin Crossover Nanocomposites

Abstract: Rod-like gold nanoparticles are directly embedded in a 1D-polymeric spin crossover (SCO) material leading to singular Au@SCO nanohybrid architectures. The resulting architectures are designed to promote a synergetic effect between ultrafast spin-state photoswitching and photothermal properties of plasmonic nanoparticles. This synergy is evidenced by the strong modulation of the surface plasmon resonance of the gold nanorods through the spin-state switching of the SCO component and also the strong enhancement of the photoswitching efficiency compared to pure SCO particles. This remarkable synergy results from the large modulation of the dielectric properties of the SCO polymer upon its thermal switching and the enhancement of the heating of these hybrid nanostructures upon excitation of the surface plasmon resonance of the gold nanorods.

Intermediate-spin state and properties of LaCoO_3

Abstract: The electronic structure of the perovskite LaCoO$_3$ for different spin states of Co ions was calculated in the LDA+U approach. The ground state was found to be a nonmagnetic insulator with Co ions in a low-spin state. Somewhat higher in energy we found two intermediate-spin states followed by a high-spin state at significantly higher energy. The calculation results show that Co 3$d$ states of $t_{2g}$ symmetry form narrow bands which could easily localize whilst $e_g$ orbitals, due to their strong hybridization with the oxygen 2$p$ states, form a broad $\sigma^*$ band. With the increase of temperature which is simulated by the corresponding increase of the lattice parameter, the transition from the low- to intermediate-spin states occurs. This intermediate-spin (occupation $t_{2g}^5e_g^1$) can develop an orbital ordering which can account for the nonmetallic nature of LaCoO$_3$ at 90 K$<$T$<$500 K. Possible explanations of the magnetic behavior and gradual insulating-metal transition are suggested.

Heterojunction Architecture of N-Doped WO3 Nanobundles with Ce2S3 Nanodots Hybridized on a Carbon Textile Enables a Highly Efficient Flexible Photocatalyst

Abstract: The availability of robust, versatile, and efficient photocatalysts is the main bottleneck in practical applications of photocatalytic degradation of organic pollutants. Herein, N‐WO3/Ce2S3 nanotube bundles (NBs) are synthesized and successfully immobilized on a carbon textile, resulting in a flexible and conducting photocatalyst. Due to the large interfacial area between N‐WO3 and Ce2S3, the interwoven 3D carbon architecture and, more importantly, the establishment of a heterojunction between N‐WO3 and Ce2S3, the resultant photocatalyst exhibits excellent light absorption capacity and superior ability to separate photoinduced electron–hole pairs for the photocatalytic degradation of organic compounds in air and water media. Theoretical calculations confirm that the strong electronic interaction between N‐WO3 and Ce2S3 can be beneficial to the enhancement of the charge carrier transfer dynamics of the as‐prepared photocatalyst. This work provides a new protocol for constructing efficient flexible photocatalysts for application in environmental remediation.

Photocatalysis Enhanced by External Fields.

Abstract: The efficient conversion of solar energy by means of photocatalysis shows huge potential to relieve the ongoing energy crisis and increasing environmental pollution. However, unsatisfactory conversion efficiency still hinders its practical application. The introduction of external fields can remarkably enhance the photocatalytic performance of semiconductors from the inside out. This review focuses on recent advances in the application of diverse external fields, including microwaves, mechanical stress, temperature gradient, electric field, magnetic field, and coupled fields, to boost photocatalytic reactions, for applications in, for example, contaminant degradation, water splitting, CO2 reduction, and bacterial inactivation. The relevant reinforcement mechanisms of photoabsorption, the transport and separation of photoinduced charges, and adsorption of reagents by the external fields are highlighted. Finally, the challenges and outlook for the development of external-field-enhanced photocatalysis are presented.

Ultrahigh enhancement rate of the energy density of flexible polymer nanocomposites using core–shell BaTiO3@MgO structures as the filler

Abstract: Dielectric energy storage capacitors are critical components widely used in electronic equipment and power systems due to their advantages of ultrahigh power density and high voltage. Herein, a novel core–shell BaTiO3@MgO (BT@MO) nanostructure was fabricated, in which highly insulating MgO was directly coated on a continuous ferroelectric nanoparticle BaTiO3 shell through a chemical precipitation method to improve the breakdown strength and electric displacement under high electric field. A large electric displacement (D ≈ 9.8 μC cm−2 under 571.4 MV m−1) was observed along with a high discharge energy density (Ud ≈ 19.0 J cm−3) for BT@MO/P(VDF-HFP) composites, which was 187% higher than that for a P(VDF-HFP) film when the filler content was 3 wt%. The enhancement rate of Ud in this study achieved the highest level among the reported results. It was revealed that the highly insulating MgO shell can enhance the breakdown strength by preventing charge injection from electrodes and impeding the development of electrical stress during the breakdown process, as confirmed by the leakage current measurements and the finite element simulations. The core–shell BT@MO structured filler provided an effective way to improve the energy storage properties of the polymer-based dielectrics.