Different dopant strategies are currently under investigation in order to overcome the many problems that limit the commercial viability of BiFeO 3-based ceramic devices. Neodymium substitution onto the A site of the perovskite lattice provokes significant changes in the crystal structure of the parent material which can derive in enhanced multiferroic properties, but the conductivity in the bulk system is still too high. Titanium doping on the other hand generates a distinctive micro-nanostructure in the consolidated ceramics which can largely increase the dc resistivity of the whole material. A combination of these two effects is here attempted in a co-doping approach which evidences that the microstructural effect caused upon Ti-doping, provoking a reduction of the leakage currents, eventually allows the co-doped material to capitalize on the unique piezoelectric and magnetic properties structurally triggered by the Nddoping.
In the search of multiferroic materials with enhanced magnetoelectric response, the BiFeO 3 -Bi 4 Ti 3 O 12 composite system has been proposed as a promising candidate. However, in order to ensure an effective coupling between the antiferromagnetic and the ferroelectric order parameters, a high structural quality of the oxide heterostructure (well-matched interface) must be attained. This implies the absence of any interdiffusion process across the interface during the consolidation of the composite assembly. In this contribution we have analysed the different diffusion scenarios that could be established in this nominal BiFeO 3 -Bi 4 Ti 3 O 12 system as a function of the specific reactivity of the involved compounds. The obtained results clearly identify how and when that diffusion is produced, so now it can be controlled to ensure the maximum exploitation of the potential multiferroic properties of this candidate system.
This paper highlights the contribution of transmission electron microscopy (TEM) when combined with scanning electron microscopy and energy-dispersive X-ray microanalysis (SEM/XEDS) to characterize objects in archaeology. The application of TEM in archaeology is not yet a common tool, but it may provide data that are significant to understanding pre-Columbian gold metallurgy, specifically the gilding and silvering methods. Two gilded rods were studied using a combination of TEM and SEM/XEDS techniques. The objects were found at the Atacames archaeological site, in the Esmeraldas region, Ecuador, which was occupied between AD 750 and 1526 by the Atacames culture. The microchemical and structural results of the inner and the external gilded part of the artefacts support the hypothesis of a gold diffusion to the surface enhanced by chemical treatment with chloride-rich solutions, heating and successive annealing processes. The present study reveals that microstructural investigation by TEM provides useful information with which to investigate the techniques used to modify the chemical surface composition of pre-Columbian artefacts.
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