No abstract

In the present work, we show how exposure to electric fields during a high-temperature treatment can be used to manipulate surface properties of donor-doped ceramics and thus improve their reactivity. La 0.1 Sr 0.9 TiO 3 (LSTO) nanoparticles, prepared by hydrothermal synthesis, were consolidated under air with and without external electric fields. Although neither approaches caused grain growth upon consolidation, the treatment under the influence of the electric field (i.e., flash sintering) remarkably enhanced the segregation of Sr on the material's surface. In addition, a high concentration of O − defects both in bulk as well as on the material surface was demonstrated by spectroscopic methods. This enhanced defect concentration along with the nanoscopic grain size of the field-consolidated materials is probably one of the triggering factors of their improved charge carrier mobility, as observed by impedance spectroscopy. The effect of such a perturbed defect structure on the reactivity of the materials was evaluated by the total oxidation of methane. For materials treated under the influence of electric fields, the catalytic reaction rate improved by a factor of 3 with respect to that of conventionally treated LSTO, along with a remarkable decrease of the activation energy. Thus, electric-field-assisted processes, usually known for their energy-saving character, can also be deemed as an attractive, forward-looking strategy for improving functional properties of ceramics.

In the present work the effect of electric field assisted treatments, i. e. flash sintering, on the physicochemical properties and surface reactivity of SrTiO3 nanoparticles is investigated. The materials were prepared by a hydrothermal approach and consolidated at high temperatures by conventional and electric field assisted procedures. The exposure to an electric field from 300 to 900 V/cm allowed rapid consolidation with progressive reduction of the grain growth and the shrinkage of the specific surface area to 22% and 43%, respectively. XPS analyses evidenced increasing Sr segregation at the surface if voltage was applied during the treatment. The corresponding presence of Sr vacancies in the perovskite lattice was demonstrated by ESR spectroscopy. Both techniques pointed out the appearance of highly oxidative O− species in all ceramics. The materials reactivity was investigated by methane oxidation, chosen as model high temperature catalytic reaction. With respect to conventionally treated SrTiO3, the surface area normalized reaction rate significantly improved for the ceramics exposed to electric field, until a maximum of three times for the material treated at 900 V/cm. Such enhanced properties were ascribed to the larger extent of Sr enrichment and in particular to the correlated field‐induced defect structure perturbation.

In the present work, nanostructured perovskite oxides with improved reactivity, tunable morphology, and different forms (powder, thin films) were prepared using acrylic molecules such as acrylamide, acrylic acid, and methacrylic acid as novel chelating agents in a straightforward fashion. The approach, developed for LaCoO3, was also applied to oxides of the type LaMO3 (M = Fe, Ni), SrTiO3, and solid solutions thereof. The polymer-to-oxide evolution followed by XRD and IR showed merely a minimal amount of carbonate residuals even at temperatures as low as 600 °C. The different cross-linking degree of the polymeric compounds influenced the material crystallization leading to oxides with different grain sizes at the same calcination temperature. Among the prepared perovskites, acrylamide-derived LaCoO3 exhibited the highest oxygen surface reactivity as demonstrated by XPS and TPD measurements. As a result, the materials showed enhanced catalytic performance, leading to complete oxidation of CO at approximately 200 °C, which was almost 100 °C lower than for citric-acid-based samples. Finally, by exploiting the UV photopolymerization of the acrylic group, homogeneous, crystalline perovskite thin films of optical quality were successfully prepared through a straightforward spin-coating approach. The findings of this work demonstrate that this novel synthesis route is a better alternative to state-of-the-art citrate-based methods for the preparation of prospective catalysis, sensing, and energy conversion materials of high purity, activity, and tunable form.