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Due to environmental concerns, extensive research has been carried out to develop high-performance lead-free piezoceramics capable of replacing commercial lead-based materials. The lead-free (Ba0.7Ca0.3)TiO3 -Ba(Zr0.2Ti0.8)O3 system has emerged as a candidate for room temperature transducer applications because a high piezoelectric charge coefficient is achieved in this system for compositions at the morphotropic phase boundary. However, conventional ceramic processing of these eco-friendly piezoceramics demands high energy consumption because long-lasting, high-temperature heat treatments are needed, which often lead to microstructural degradation that compromises the material reliability. Field-assisted flash sintering has started to be explored since the application of an adequate electric field was shown to significantly reduce the sintering time and temperature, thereby controlling grain growth. In this work, Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics are obtained by current-controlled flash sintering of mechanosynthesized nanopowders. Exhaustive control of the sintering parameters allows tailoring of the microstructure, which allows dense fine-grained flash-sintered ceramics exhibiting a high electric field-induced strain response to be obtained., This work was supported by the Agencia Estatal de Investigación (AEI), Spain, projects PGC2018-099158-B-I00 and PID2021–122708OB-C33. S. L-B. thanks Agència de Gestió d′Ajuts Universitaris i de Recerca (AGAUR), Catalonia, Spain, for the FI-SDUR contract (2020 FISDU 00489). The authors acknowledge the ESRF (The European Synchrotron) for provision of synchrotron radiation facilities, and we would like to thank the BM25 (SpLine) staff for assistance in using the beamline., Peer Reviewed, Postprint (published version)

Psidium guajava L. and Psidium friedrichsthalianum Nied are part of the Psidium species native to America. Nowadays, it is essential to study the phenolic compound (PC) profile and their changes during digestion and the fractions available for absorption. This study aimed to characterize the PC profile in some Psidium species and their bioaccessibility (BA). Fifty-seven compounds were identified, and forty-six belonged to ten different phenolic classes. PC profiles showed significant differences between the species and the intestinal fraction P. friedrichsthalianum Nied. showed the highest PC content, although it mostly belonged to non-extractable polyphenols. This leads to the lowest BA (37%); P. guajava L. ‘Morada’ showed the highest (47%). Hydroxycinnamic acids were the most stable PC after gastrointestinal digestion. This study showed relevant differences in the PC content and profile of different Psidium species and changes between the PC in the original matrix and those released in the different stages of gastrointestinal digestion.

[EN] Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) stands out among lead-free ferroelectric oxides under consideration to replace state-of-the-art high-sensitivity piezoelectric Pb(Zr,Ti)O3, for a range of energy conversion ceramic technologies. However, the best performances have been reported for very coarse-grained materials, and attempts to refine microstructure below 10 µm grain size consistently result in significant property degradation. Here a comprehensive study of the grain size effects on the properties of BCZT across the micron scale is reported, down to the verge of the submicron one. Results show a distinctive early evolution of properties for grain sizes between 1 and 5 µm. For the larger sizes in this range, an opposite effect is found for the piezoelectric charge coefficient and electric field-induced strain with respect to the very coarse-grained material, while very good overall performance is maintained. For the lower sizes, relaxor features appear, yet materials can still be poled indicating their ferroelectric nature. This strongly resembles size effects in the Pb(Mg1/3Nb2/3)O3-PbTiO3 system, driven by the slowing down of the relaxor to ferroelectric transition with size reduction, though kinetics seem to slow down across much larger grain sizes for BCZT. Concomitant changes in the polymorphic phase coexistence are described and discussed by synchrotron X-ray diffraction.

[EN] Due to environmental concerns, extensive research has been carried out to develop high-performance lead-free piezoceramics capable of replacing commercial lead-based materials. The lead-free (BaCa)TiO −Ba(ZrTi)O system has emerged as a candidate for room temperature transducer applications because a high piezoelectric charge coefficient is achieved in this system for compositions at the morphotropic phase boundary. However, conventional ceramic processing of these eco-friendly piezoceramics demands high energy consumption because long-lasting, high-temperature heat treatments are needed, which often lead to microstructural degradation that compromises the material reliability. Field-assisted flash sintering has started to be explored since the application of an adequate electric field was shown to significantly reduce the sintering time and temperature, thereby controlling grain growth. In this work, BaCaZrTiO ceramics are obtained by current-controlled flash sintering of mechanosynthesized nanopowders. Exhaustive control of the sintering parameters allows tailoring of the microstructure, which allows dense fine-grained flash-sintered ceramics exhibiting a high electric field-induced strain response to be obtained.

[EN] Aurivillius layered oxides with general formula (Bi2O2)(Am-1BmO3m+1) stand out among room-temperature magnetoelectric multiferroics for their large magnetization. However, despite extensive research, there is an obvious lack of understanding of their magnetism. The chemical design strategy for obtaining multiferroism involves the incorporation of M3+ magnetic cations at the B-site of well-known ferroelectric compounds such as Bi4Ti3O12 (m = 3). We report here a study of the magnetism and dielectric properties of Aurivillius Bi4Ti3 - 2xNbxFexO12 phases with x ≥ 1 up to 1.2, which correspond to magnetic cation fractions at the B site between 0.33 and 0.4 above the threshold for percolation. This is a three-layer system, less prone to the formation of intergrowths, which nominally contains Fe3+ as single magnetic species. Despite that, a rich phenomenology is uncovered. Coexisting magnetic orders are present in the Aurivillius compounds, and a Morin-like transition takes place at low temperatures. The dielectric characterization does not show any associated anomaly that could indicate a polymorphic phase transition but the appearance of relaxor-like characteristics. Possible scenarios are discussed, which involve the presence of Fe2+, cation partitioning between nonequivalent B-sites, and the development of polar nanodomains within a ferroelectric phase at a spin reorientation transition.

Lead-free ferroelectric Ba0.85Ca0.15Zr0.1Ti0.9O3 stands out among environmentally friendly alternatives to commercial Pb(Zr,Ti)O3 piezoceramics for its large piezoelectric coefficients, and it is especially suitable for applications in which thermal depoling is not an issue like bio-implanted devices. However, ceramic processing by conventional means consistently results in exaggerated grain growth, which compromises reliability and has prevented its transfer to industry. We report here the application of high-energy milling for the mechanosynthesis of nanocrystalline Ba0.85Ca0.15Zr0.1Ti0.9O3 powders with enhanced reactivity, and to the control of grain growth during ceramic processing to obtain materials with tailored microstructures and decreasing grain sizes down to the sub-10 µm range. Characterization of the electrical and electromechanical properties was accomplished and uncovered triggering of a new mechanism for very large strain under electric field in fine-grained ceramics. Process optimization by precursor selection and preliminary up-scaling studies are also presented.