We present the experimental phase function, degree of linear polarization (DLP), and linear depol... more We present the experimental phase function, degree of linear polarization (DLP), and linear depolarization (δ L ) curves of a set of forsterite samples representative of low-absorbing cosmic dust particles. The samples are prepared using state-of-the-art size-segregating techniques to obtain narrow size distributions spanning a broad range of the scattering size parameter domain. We conclude that the behavior of the phase function at the side- and back-scattering regions provides information on the size regime, the position and magnitude of the maximum of the DLP curve are strongly dependent on particle size, the negative polarization branch is mainly produced by particles with size parameters in the ∼6 to ∼20 range, and the δ L is strongly dependent on particle size at all measured phase angles except for the exact backward direction. From a direct comparison of the experimental data with computations for spherical particles, it becomes clear that the use of the spherical model for...
<p>The atmosphere of Mars is driven by different cycles – seasonal cy... more <p>The atmosphere of Mars is driven by different cycles – seasonal cycles of temperature, dust, ice, water vapour, CO2, etc. – which are coupled through transport: dust is blown from the surface by winds, carried aloft where it absorbs solar radiation and heats the atmosphere, impacting temperature, composition and winds. Formation of water ice crystals scavenges dust back from the surface. Water, being involved in the creation processes of clouds, is one of the most important species in the atmosphere. It controls the stability of the atmosphere, dominates its chemistry, and has a radiative impact through the formation of clouds.</p> <p>Dust is present everywhere on Mars, yet its abundance, physical properties, size distribution as well as impact on the composition, structure and dynamics of the atmosphere has today only barely been addressed and understood. However, knowledge of the characteristics of aerosols (such as dust, ices, clouds and haze) is crucial for the interpretation of the IR and UV spectra because they absorb in these spectral regions, and their absorption signature overlaps the absorption features of other species (such as O3 in the UV), and they regulate the travelling path of light in the atmosphere through absorption and (multiple) scattering. Their impact is difficult to accurately estimate because their spectral characteristics are not known with enough accuracy.</p> <p>The goal of the ROADMAP project (ROle and impAct of Dust and clouds in the Martian AtmosPhere)<strong> </strong>is to better characterize the Martian dust and clouds in terms of size, shape and loading within the atmosphere, but also to provide laboratory reference data which will be used to improve our knowledge on the genesis, transport and impact of dust and clouds on the Martian atmosphere.</p> <p>The team behind the RoadMap project brings together the laboratory community, scientists involved in space missions and numerical modellers to promote synergies through their different perspectives and experiences: laboratory scientists understand the reference data and know-how to extract the most value from their experiments; mission scientists know the intricacies and potential of the instruments and the details of their calibration; numerical modellers know what data, information and parameters are most pertinent to their simulations and how best to interpret the results.</p> <p>We will describe the methodology behind the project and show how we intend to improve space exploration (observation and modelling of the atmosphere) using new laboratory results (dust resuspension induced by saltation, scattering properties, etc).</p> <p> </p> <p><strong>The RoadMap (ROle and impAct of Dust and clouds in the Martian AtmosPhere) </strong>project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101004052.</p> <div id="ConnectiveDocSignExtentionInstalled" data-extension-version="1.0.4"></div>
In recent decades, the demand for biomedical imaging tools has grown very rapidly as a key featur... more In recent decades, the demand for biomedical imaging tools has grown very rapidly as a key feature for biomedical research and diagnostic applications. Particularly, fluorescence imaging has gained increased attention as a non-invasive, inexpensive technique that allows real-time imaging. However, tissue auto-fluorescence under external illumination, together with a weak tissue penetration of low wavelength excitation light, largely restricts the application of the technique. Accordingly, new types of fluorescent labels are currently being investigated and, in this search, phosphorescent nanoparticles promise great potential, as they combine the interesting size-dependent properties of nanoscale materials with a long-lasting phosphorescence-type emission that allows optical imaging well after excitation (so avoiding autofluorescence). In this work, core-shell structures consisting of SrAlO:Eu,Dy luminescent cores encapsulated within a biocompatible silica shell were prepared, showin...
Ca0.5Zr2(PO4)3 and Ca0.45Eu0.05Zr2(PO4)3 nanophosphors have been synthesized by a sol–gel process... more Ca0.5Zr2(PO4)3 and Ca0.45Eu0.05Zr2(PO4)3 nanophosphors have been synthesized by a sol–gel process under acid and basic conditions. In order to achieve the reduction of Eu3+ to Eu2+, europium-doped samples were treated in a reducing atmosphere flow. The effects of the different synthesis conditions and the partial substitution of calcium by europium ions on the structure of the samples were analyzed by x-ray diffraction (XRD) transmission electron microscopy (TEM) and micro-Raman spectroscopy. Luminescence and magnetic properties were investigated by photoluminescence (PL) spectroscopy and magnetic susceptibility measurements. XRD patterns can be indexed to a rhombohedral symmetry of space group R-3 with Z = 6, consistent with a NASICON-type structure. A higher crystallinity was found in the samples prepared under basic conditions. TEM images of all the synthesized samples show spherically shaped particles. A broadening of the Raman bands as a result of non-equivalent vibrations of the orthophosphate groups is observed for samples prepared under acid conditions. The same effect was found when calcium is substituted by europium into the Ca0.5Zr2(PO4)3 host. PL spectra exhibit strong emission in the blue-green spectral range due to Eu2+ 4f65d1-4f7 transitions and no evidence of Eu3+ emission. Magnetic measurements confirm the 2+ oxidation state of europium ions in all samples.
Boletín de la Sociedad Española de Cerámica y Vidrio, 2015
Resumen Muestras de composicion Ca 0,45 Eu 0,05 Zr 2 (PO 4 ) 3 se sintetizaron utilizando un meto... more Resumen Muestras de composicion Ca 0,45 Eu 0,05 Zr 2 (PO 4 ) 3 se sintetizaron utilizando un metodo de preparacion que transcurre en 2 etapas: uso de un proceso sol-gel empleando medios de reaccion acido (pH ≈ 2) y basico (pH ≈ 10) y un calentamiento posterior de los polvos precursores en corriente de N 2 :H 2 (90:10) con el objeto de estabilizar el estado de oxidacion 2+ en el europio. Los perfiles de difraccion de rayos X obtenidos muestran reflexiones caracteristicas de una estructura tipo NASICON de simetria romboedrica y grupo espacial R-3. Se aprecian maximos de reflexion mas intensos para las muestras que se preparan usando un medio de reaccion basico. Las medidas magneticas confirman el estado de oxidacion 2+ del europio en las muestras sintetizadas. Las imagenes de microscopia hacen visibles particulas de morfologia esferica y tamano nanometrico, en buen acuerdo con los resultados de difraccion de rayos X, lo que indica que estas muestras pueden resultar de utilidad en ciertos dispositivos luminiscentes.
The present contribution deals with the development of an empirical approach that will describe t... more The present contribution deals with the development of an empirical approach that will describe the evolution of the breakdown voltage in ZnO-based varistors as a function of the sintering variables. This relationship is described through the kinetic analysis of the grain growth process. It is found that for a certain range of sintering conditions the varistor breakdown voltage could be
Emission of dust up to a few microns in size by impacts of sand grains during saltation is though... more Emission of dust up to a few microns in size by impacts of sand grains during saltation is thought to be one source of dust within the Martian atmosphere. To study this dust fraction, we carried out laboratory impact experiments. Small numbers of particles of about 200 μm in diameter impacted a simulated Martian soil (bimodal Mars Global Simulant). Impacts occurred at angles of ∼18° in vacuum with an impact speed of ∼1 m s−1. Ejected dust was captured on adjacent microscope slides and the emitted particle size distribution (PSD) was found to be related to the soil PSD. We find that the ejection of clay-sized dust gets increasingly harder the smaller these grains are. However, in spite of strong cohesive forces, individual impacts emit dust of 1 μm and less, i.e., dust in the size range that can be suspended in the Martian atmosphere. More generally, the probability of ejecting dust of a given size can be characterized by a power law in the size range between 0.5 and 5 μm (diameter).
ABSTRACT Ceramic composites of the mixed system (BaTiO3)x(NiFe2O4)1−x (x = 1, 0.8, 0.65, 0.6, 0.5... more ABSTRACT Ceramic composites of the mixed system (BaTiO3)x(NiFe2O4)1−x (x = 1, 0.8, 0.65, 0.6, 0.5, 0.2, 0) have been prepared by hydrothermal synthesis and characterized through dielectric and magnetic measurements. It is shown that, when compared with the first-order phase transition of pure BaTiO3, the ferroelectric response of this mixed system is dramatically smeared by the presence of ferrite and eventually disappears around x ≈ 0.65. The peak of the dielectric constant becomes increasingly smoothed with composition, also diminishing its maximum value as the frequency increases. Moreover, the magnetic behavior is not suppressed by the presence of the ferroelectric perovskite and just qualitative changes occur in the hysteresis parameters on the whole compositional range.
BiFeO3 single-phase thin films with an effective and tuneable multiferroic response are obtained ... more BiFeO3 single-phase thin films with an effective and tuneable multiferroic response are obtained in aqueous media by using mild processing conditions.
Anatase TiO2 has become a material of great interest for photocatalytic production of hydrogen, e... more Anatase TiO2 has become a material of great interest for photocatalytic production of hydrogen, environmental purification and solar energy conversion. Among the key parameters boosting the photocatalytic efficiency of the anatase nanoparticles, an increased light absorption to expand its optical response to the visible region, together with an improved charge separation of the photo-generated electrons and holes, can be enumerated. In this work, yellow-coloured, single-phase anatase nanoparticles have been obtained using a simple two-step solvothermal routine which requires no external addition of dopants, nor the use of a harassing/aggressive synthesis atmosphere. The obtained powders display a lowered bandgap (<3.0 eV) and significantly reduce the recombination processes, eventually leading to an improved photocatalytic performance under visible light, as exemplified by an enhanced degradation of phenol. This exceptional response is linked to the presence of intrinsic defects in the yellowish particles and, hence, the specific conditions of the proposed methodology become crucial to produce a propitious TiO2-defective nanomaterial capable of photo-degrade the phenol molecule, in contrast with the lack of photocatalytic activity currently exhibited by commercial photocatalysts under visible light.
Boletín de la Sociedad Española de Cerámica y Vidrio
The conventional solid state processing of bulk Ti,Sm co-doped BiFeO 3 ceramics typically produce... more The conventional solid state processing of bulk Ti,Sm co-doped BiFeO 3 ceramics typically produces a complex micro-nanostructure which exhibits an effective decrease of the leakage conductivity. This same nanostructured configuration however confines the mobility of the ferroelectric domains and in this way the potential piezoelectric response of the formulated composition remains restrained. Hereby, a two-step doping strategy based on a simple surface modification approach is proposed which eventually allows for suitably engineering the microstructural development of the material, leading to a coarsened configuration where the conductivity is kept in low levels while the piezoelectric response is satisfactorily released for practical purposes.
We present the experimental phase function, degree of linear polarization (DLP), and linear depol... more We present the experimental phase function, degree of linear polarization (DLP), and linear depolarization (δ L ) curves of a set of forsterite samples representative of low-absorbing cosmic dust particles. The samples are prepared using state-of-the-art size-segregating techniques to obtain narrow size distributions spanning a broad range of the scattering size parameter domain. We conclude that the behavior of the phase function at the side- and back-scattering regions provides information on the size regime, the position and magnitude of the maximum of the DLP curve are strongly dependent on particle size, the negative polarization branch is mainly produced by particles with size parameters in the ∼6 to ∼20 range, and the δ L is strongly dependent on particle size at all measured phase angles except for the exact backward direction. From a direct comparison of the experimental data with computations for spherical particles, it becomes clear that the use of the spherical model for...
<p>The atmosphere of Mars is driven by different cycles – seasonal cy... more <p>The atmosphere of Mars is driven by different cycles – seasonal cycles of temperature, dust, ice, water vapour, CO2, etc. – which are coupled through transport: dust is blown from the surface by winds, carried aloft where it absorbs solar radiation and heats the atmosphere, impacting temperature, composition and winds. Formation of water ice crystals scavenges dust back from the surface. Water, being involved in the creation processes of clouds, is one of the most important species in the atmosphere. It controls the stability of the atmosphere, dominates its chemistry, and has a radiative impact through the formation of clouds.</p> <p>Dust is present everywhere on Mars, yet its abundance, physical properties, size distribution as well as impact on the composition, structure and dynamics of the atmosphere has today only barely been addressed and understood. However, knowledge of the characteristics of aerosols (such as dust, ices, clouds and haze) is crucial for the interpretation of the IR and UV spectra because they absorb in these spectral regions, and their absorption signature overlaps the absorption features of other species (such as O3 in the UV), and they regulate the travelling path of light in the atmosphere through absorption and (multiple) scattering. Their impact is difficult to accurately estimate because their spectral characteristics are not known with enough accuracy.</p> <p>The goal of the ROADMAP project (ROle and impAct of Dust and clouds in the Martian AtmosPhere)<strong> </strong>is to better characterize the Martian dust and clouds in terms of size, shape and loading within the atmosphere, but also to provide laboratory reference data which will be used to improve our knowledge on the genesis, transport and impact of dust and clouds on the Martian atmosphere.</p> <p>The team behind the RoadMap project brings together the laboratory community, scientists involved in space missions and numerical modellers to promote synergies through their different perspectives and experiences: laboratory scientists understand the reference data and know-how to extract the most value from their experiments; mission scientists know the intricacies and potential of the instruments and the details of their calibration; numerical modellers know what data, information and parameters are most pertinent to their simulations and how best to interpret the results.</p> <p>We will describe the methodology behind the project and show how we intend to improve space exploration (observation and modelling of the atmosphere) using new laboratory results (dust resuspension induced by saltation, scattering properties, etc).</p> <p> </p> <p><strong>The RoadMap (ROle and impAct of Dust and clouds in the Martian AtmosPhere) </strong>project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101004052.</p> <div id="ConnectiveDocSignExtentionInstalled" data-extension-version="1.0.4"></div>
In recent decades, the demand for biomedical imaging tools has grown very rapidly as a key featur... more In recent decades, the demand for biomedical imaging tools has grown very rapidly as a key feature for biomedical research and diagnostic applications. Particularly, fluorescence imaging has gained increased attention as a non-invasive, inexpensive technique that allows real-time imaging. However, tissue auto-fluorescence under external illumination, together with a weak tissue penetration of low wavelength excitation light, largely restricts the application of the technique. Accordingly, new types of fluorescent labels are currently being investigated and, in this search, phosphorescent nanoparticles promise great potential, as they combine the interesting size-dependent properties of nanoscale materials with a long-lasting phosphorescence-type emission that allows optical imaging well after excitation (so avoiding autofluorescence). In this work, core-shell structures consisting of SrAlO:Eu,Dy luminescent cores encapsulated within a biocompatible silica shell were prepared, showin...
Ca0.5Zr2(PO4)3 and Ca0.45Eu0.05Zr2(PO4)3 nanophosphors have been synthesized by a sol–gel process... more Ca0.5Zr2(PO4)3 and Ca0.45Eu0.05Zr2(PO4)3 nanophosphors have been synthesized by a sol–gel process under acid and basic conditions. In order to achieve the reduction of Eu3+ to Eu2+, europium-doped samples were treated in a reducing atmosphere flow. The effects of the different synthesis conditions and the partial substitution of calcium by europium ions on the structure of the samples were analyzed by x-ray diffraction (XRD) transmission electron microscopy (TEM) and micro-Raman spectroscopy. Luminescence and magnetic properties were investigated by photoluminescence (PL) spectroscopy and magnetic susceptibility measurements. XRD patterns can be indexed to a rhombohedral symmetry of space group R-3 with Z = 6, consistent with a NASICON-type structure. A higher crystallinity was found in the samples prepared under basic conditions. TEM images of all the synthesized samples show spherically shaped particles. A broadening of the Raman bands as a result of non-equivalent vibrations of the orthophosphate groups is observed for samples prepared under acid conditions. The same effect was found when calcium is substituted by europium into the Ca0.5Zr2(PO4)3 host. PL spectra exhibit strong emission in the blue-green spectral range due to Eu2+ 4f65d1-4f7 transitions and no evidence of Eu3+ emission. Magnetic measurements confirm the 2+ oxidation state of europium ions in all samples.
Boletín de la Sociedad Española de Cerámica y Vidrio, 2015
Resumen Muestras de composicion Ca 0,45 Eu 0,05 Zr 2 (PO 4 ) 3 se sintetizaron utilizando un meto... more Resumen Muestras de composicion Ca 0,45 Eu 0,05 Zr 2 (PO 4 ) 3 se sintetizaron utilizando un metodo de preparacion que transcurre en 2 etapas: uso de un proceso sol-gel empleando medios de reaccion acido (pH ≈ 2) y basico (pH ≈ 10) y un calentamiento posterior de los polvos precursores en corriente de N 2 :H 2 (90:10) con el objeto de estabilizar el estado de oxidacion 2+ en el europio. Los perfiles de difraccion de rayos X obtenidos muestran reflexiones caracteristicas de una estructura tipo NASICON de simetria romboedrica y grupo espacial R-3. Se aprecian maximos de reflexion mas intensos para las muestras que se preparan usando un medio de reaccion basico. Las medidas magneticas confirman el estado de oxidacion 2+ del europio en las muestras sintetizadas. Las imagenes de microscopia hacen visibles particulas de morfologia esferica y tamano nanometrico, en buen acuerdo con los resultados de difraccion de rayos X, lo que indica que estas muestras pueden resultar de utilidad en ciertos dispositivos luminiscentes.
The present contribution deals with the development of an empirical approach that will describe t... more The present contribution deals with the development of an empirical approach that will describe the evolution of the breakdown voltage in ZnO-based varistors as a function of the sintering variables. This relationship is described through the kinetic analysis of the grain growth process. It is found that for a certain range of sintering conditions the varistor breakdown voltage could be
Emission of dust up to a few microns in size by impacts of sand grains during saltation is though... more Emission of dust up to a few microns in size by impacts of sand grains during saltation is thought to be one source of dust within the Martian atmosphere. To study this dust fraction, we carried out laboratory impact experiments. Small numbers of particles of about 200 μm in diameter impacted a simulated Martian soil (bimodal Mars Global Simulant). Impacts occurred at angles of ∼18° in vacuum with an impact speed of ∼1 m s−1. Ejected dust was captured on adjacent microscope slides and the emitted particle size distribution (PSD) was found to be related to the soil PSD. We find that the ejection of clay-sized dust gets increasingly harder the smaller these grains are. However, in spite of strong cohesive forces, individual impacts emit dust of 1 μm and less, i.e., dust in the size range that can be suspended in the Martian atmosphere. More generally, the probability of ejecting dust of a given size can be characterized by a power law in the size range between 0.5 and 5 μm (diameter).
ABSTRACT Ceramic composites of the mixed system (BaTiO3)x(NiFe2O4)1−x (x = 1, 0.8, 0.65, 0.6, 0.5... more ABSTRACT Ceramic composites of the mixed system (BaTiO3)x(NiFe2O4)1−x (x = 1, 0.8, 0.65, 0.6, 0.5, 0.2, 0) have been prepared by hydrothermal synthesis and characterized through dielectric and magnetic measurements. It is shown that, when compared with the first-order phase transition of pure BaTiO3, the ferroelectric response of this mixed system is dramatically smeared by the presence of ferrite and eventually disappears around x ≈ 0.65. The peak of the dielectric constant becomes increasingly smoothed with composition, also diminishing its maximum value as the frequency increases. Moreover, the magnetic behavior is not suppressed by the presence of the ferroelectric perovskite and just qualitative changes occur in the hysteresis parameters on the whole compositional range.
BiFeO3 single-phase thin films with an effective and tuneable multiferroic response are obtained ... more BiFeO3 single-phase thin films with an effective and tuneable multiferroic response are obtained in aqueous media by using mild processing conditions.
Anatase TiO2 has become a material of great interest for photocatalytic production of hydrogen, e... more Anatase TiO2 has become a material of great interest for photocatalytic production of hydrogen, environmental purification and solar energy conversion. Among the key parameters boosting the photocatalytic efficiency of the anatase nanoparticles, an increased light absorption to expand its optical response to the visible region, together with an improved charge separation of the photo-generated electrons and holes, can be enumerated. In this work, yellow-coloured, single-phase anatase nanoparticles have been obtained using a simple two-step solvothermal routine which requires no external addition of dopants, nor the use of a harassing/aggressive synthesis atmosphere. The obtained powders display a lowered bandgap (<3.0 eV) and significantly reduce the recombination processes, eventually leading to an improved photocatalytic performance under visible light, as exemplified by an enhanced degradation of phenol. This exceptional response is linked to the presence of intrinsic defects in the yellowish particles and, hence, the specific conditions of the proposed methodology become crucial to produce a propitious TiO2-defective nanomaterial capable of photo-degrade the phenol molecule, in contrast with the lack of photocatalytic activity currently exhibited by commercial photocatalysts under visible light.
Boletín de la Sociedad Española de Cerámica y Vidrio
The conventional solid state processing of bulk Ti,Sm co-doped BiFeO 3 ceramics typically produce... more The conventional solid state processing of bulk Ti,Sm co-doped BiFeO 3 ceramics typically produces a complex micro-nanostructure which exhibits an effective decrease of the leakage conductivity. This same nanostructured configuration however confines the mobility of the ferroelectric domains and in this way the potential piezoelectric response of the formulated composition remains restrained. Hereby, a two-step doping strategy based on a simple surface modification approach is proposed which eventually allows for suitably engineering the microstructural development of the material, leading to a coarsened configuration where the conductivity is kept in low levels while the piezoelectric response is satisfactorily released for practical purposes.
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