Experimental evidence of charged domain walls in lead-free ferroelectric ceramics: Light-driven nanodomain switching

The control of ferroelectric domain walls at the nanometric level leads to novel interfacial properties and functionalities. In particular, the comprehension of charged domain walls, CDWs, lies at the frontier of future nanoelectronic research. Whereas many of the effects have been demonstrated for ideal archetypes, such as single crystals, and/or thin films, a similar control of CDWs on polycrystalline ferroelectrics has not been achieved. Here, we unambiguously show the presence of charged domain walls on a lead-free (K,Na)NbO 3 polycrystalline system. The appearance of CDWs is observed in situ by confocal Raman microscopy and second harmonic generation microscopy. CDWs produce an internal strain gradient within each domain. Specifically, the anisotropic strain develops a crucial piece in the ferroelectric domain switching due to the coupling between the polarization of light and the ferroelectric polarization of the nanodomain in the (K,Na)NbO 3 ceramic. This effect leads to the tuning of the ferroelectric domain switching by means of the light polarization angle. Our results will help to understand the relevance of charged domain walls on the ferroelectric domain switching process and may facilitate the development of domain wall nanoelectronics by remote light control utilizing polycrystalline ferroelectricsThis work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under the projects MAT201348009-C4-1-P, MAT2013-43301-R and MAT2016-76106-R, the Spanish National Research Council (CSIC) under the project NANOMIND CSIC 201560E068 and the Comunidad de Madrid under the grant S2013/MIT-274

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

Unraveling grain growth of metallic tungsten: Investigating the nanoscale realm of hydrogen reduction of tungsten oxides

peer reviewedThis paper focuses on the experimental observation of tungsten grain evolution during the process of hydrogen reduction of tungsten trioxide. The objective is to gain insights into the grain size distribution (GSD) evolution and morphology changes of metallic tungsten. The study employs an amalgamation of conventional characterization techniques —such as TGA, SEM-EDS, TEM and XRD— alongside cutting-edge techniques like phase contrast nano-tomography from synchrotron sources. Conducted as a quasi in-situ study, this research offers the opportunity to observe the transient evolution of the formed metallic tungsten phase within its precursor WO2 particles. The paper presents and discusses quantitative results concerning the evolution of GSD and morphological changes, encompassing growth rates of both crystallites and grains of the synthesized metallic phase. Additionally, the quasi in-situ study highlights the dependence of grain size on water concentration during the reduction process. The qualitative and quantitative findings contribute to a more nuanced understanding of the kinetics of grain growth of metallic tungsten and offer insights into the intricate interplay between reduction parameters, GSD evolution and morphological changes. Gaining a deeper understanding of the underlying mechanisms driving the changes in GSD establishes a foundation for predictive theory with immediate academic and industrial impact.R-AGR-3749 - C19/MS/13564670/TuCaNG - ESTUPINAN DONOSO Alvar

Combining X-Ray Whole Powder Pattern Modeling, Rietveld and Pair Distribution Function Analyses as a Novel Bulk Approach to Study Interfaces in Heteronanostructures : Oxidation Front in FeO/Fe3O4 Core/Shell Nanoparticles as a Case Study

Altres ajuts: Beatriu de Pinos Program (2011 BPB 00209)Understanding the microstructure in heterostructured nanoparticles is crucial to harnessing their properties. Although microscopy is ideal for this purpose, it allows for the analysis of only a few nanoparticles. Thus, there is a need for structural methods that take the whole sample into account. Here, a novel bulk-approach based on the combined analysis of synchrotron X-ray powder diffraction with whole powder pattern modeling, Rietveld and pair distribution function is presented. The microstructural temporal evolution of FeO/FeO core/shell nanocubes is studied at different time intervals. The results indicate that a two-phase approach (FeO and FeO) is not sufficient to successfully fit the data and two additional interface phases (FeO and FeO) are needed to obtain satisfactory fits, i.e., an onion-type structure. The analysis shows that the FeO phases grow to some extent (≈1 nm) at the expense of the FeO core. Moreover, the FeO core progressively changes its stoichiometry to accommodate more oxygen. The temporal evolution of the parameters indicates that the structure of the FeO/FeO nanocubes is rather stable, although the exact interface structure slightly evolves with time. This approach paves the way for average studies of interfaces in different kinds of heterostructured nanoparticles, particularly in cases where spectroscopic methods have some limitations

Combining X-ray whole powder pattern modeling, rietveld and pair distribution function analyses as a novel bulk approach to study interfaces in heteronanostructures: Oxidation front in FeO/Fe3O4 core/shell nanoparticles as a case study

Understanding the microstructure in heterostructured nanoparticles is crucial to harnessing their properties. Although microscopy is ideal for this purpose, it allows for the analysis of only a few nanoparticles. Thus, there is a need for structural methods that take the whole sample into account. Here, a novel bulk‐approach based on the combined analysis of synchrotron X‐ray powder diffraction with whole powder pattern modeling, Rietveld and pair distribution function is presented. The microstructural temporal evolution of FeO/Fe3O4 core/shell nanocubes is studied at different time intervals. The results indicate that a two‐phase approach (FeO and Fe3O4) is not sufficient to successfully fit the data and two additional interface phases (FeO and Fe3O4) are needed to obtain satisfactory fits, i.e., an onion‐type structure. The analysis shows that the Fe3O4 phases grow to some extent (≈1 nm) at the expense of the FeO core. Moreover, the FeO core progressively changes its stoichiometry to accommodate more oxygen. The temporal evolution of the parameters indicates that the structure of the FeO/Fe3O4 nanocubes is rather stable, although the exact interface structure slightly evolves with time. This approach paves the way for average studies of interfaces in different kinds of heterostructured nanoparticles, particularly in cases where spectroscopic methods have some limitations.R.U.I. acknowledges CAPES and CNPq (No. 206983/2014‐0) Brazilian agencies. A.G.R. and J.N. thanks the support of the Generalitat de Catalunya through the 2017‐SGR‐292 project and the Beatriu de Pinos Program (2011 BPB 00209) and the Spanish Ministerio de Economía y Competitividad (MINECO) through the MAT2016‐77391‐R project. I.P. was supported by the National Research Fund of Luxembourg (Grant No. FNR‐Inter2015/LRSF). A.L.‐O. acknowledges the MINECO through the Juan de la Cierva Program (IJCI‐2014‐21530). X.T. would like to acknowledge the financial support from the MINECO projects MAT2015‐67593‐P and BIA2014‐57658‐C2‐1‐R. The ALBA Synchrotron is acknowledged for the provision of beamtime and the MSPD beamline staff is for their help during the XRD measurements. Dr. Luis G. Martinez from IPEN/CNEN is acknowledged for useful discussions about XRD techniques. Dr. Paolo Scardi from Università degli Studi di Trento is acknowledged for the helpful discussions about WPPM and for providing PM2K v.3 software. ICN2 is funded by the CERCA Programme/Generalitat de Catalunya. ICN2 also acknowledges support from the Severo Ochoa Program (MINECO, Grant No. SEV‐2013‐0295).Peer reviewe

Cation distribution of Mn-Zn ferrite nanoparticles using pair distribution function analysis and resonant X-ray scattering

Mn-Zn ferrite nanoparticles were synthesized by chemical co-precipitation method and analysed using X-ray synchrotron diffraction data. Pair distribution function (PDF) analysis was used to probe the local structure and revealed that the first-neighbour distances of Fe-Fe and Mn-Zn in the 3.0 up to 3.5 Å range are different from the ones usually reported in the literature. For the sample with the best magnetic behaviour, resonant X-ray scattering (RXS) using three energies close to the absorption edges of Mn, Zn and Fe was applied to determine the cation distribution which explained the previous result from PDF analysis

Cation distribution of Mn-Zn ferrite nanoparticles using pair distribution function analysis and resonant X-ray scattering

Mn-Zn ferrite nanoparticles were synthesized by chemical co-precipitation method and analysed using X-ray synchrotron diffraction data. Pair distribution function (PDF) analysis was used to probe the local structure and revealed that the first-neighbour distances of Fe-Fe and Mn-Zn in the 3.0 up to 3.5 Å range are different from the ones usually reported in the literature. For the sample with the best magnetic behaviour, resonant X-ray scattering (RXS) using three energies close to the absorption edges of Mn, Zn and Fe was applied to determine the cation distribution which explained the previous result from PDF analysis

Aluminum Hydroxide Gel Characterization within a Calcium Aluminate Cement Paste by Combined Pair Distribution Function and Rietveld Analyses

There are many commercially important multiphase materials which contain amorphous phases, such as cement pastes, porcelains, glass-ceramics or pharmaceutical compounds. However, the analysis of amorphous phase(s) within cement matrices that contain high amounts of crystalline phase(s) is a challenge. Here, we report measurements of total scattering data quantitatively analyzed by Pair Distribution Function (PDF) minimization and Rietveld methodology to determine phase compositions including both amorphous and nanocrystalline phase contents in cement-related samples. Furthermore, laboratory techniques were used to complement the sample characterization. In addition to five reference materials, the main phase of calcium aluminate cements, CaAl2O4 hydrated at 50 °C to yield crystalline hydrogarnet, Ca3Al2(OH)12, (43wt%) and nanocrystalline aluminum hydroxide gel, Al(OH)3·0.1H2O (50wt%) was also investigated. The PDF analyses revealed that the hydroxide gel has a gibbsite local structurewith an average particle size close to 5nm. PDF and Rietveld quantitative phase analysis results fully agree.This work has been supported by Spanish MINECO through BIA2014-57658-C2-1-R and BIA2014-57658-C2-2-R, which is cofunded by FEDER, research grants. R.U.I. acknowledges funding of CNPQ, grant no. 206983/2014-0/SWE. We also thank CELLS-ALBA (Barcelona, Spain) for providing synchrotron beamtime at BL04-MSPDand Dr. Oriol Vallcorba for his assistance during the synchrotron experiment.2018-07-0