Person: Isasi Marín, Josefa
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First Name
Josefa
Last Name
Isasi Marín
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Química Inorgánica
Area
Química Inorgánica
Identifiers
6 results
Search Results
Now showing 1 - 6 of 6
Item Influence of chromium content on the optical and electrical properties of Li1+xCrxTi2-x(PO4)3(Solid State Ionics, 2013) Pérez Estébanez, Marta; Isasi Marín, Josefa; Díaz-Guerra Viejo, Carlos; Rivera Calzada, Alberto Carlos; León Yebra, Carlos; Santamaría Sánchez-Barriga, JacoboOptical and electrical properties of samples with Li1 + xCrxTi2 − x(PO4)3 composition (x = 0, 0.05 and 0.1) prepared by a low temperature sol-gel method have been investigated. XRD and Raman spectroscopy measurements respectively reveal the rhombohedral-Nasicon structure of the grown samples and a disorder of Li+ ions with increasing chromium content. Electrical properties were studied by impedance spectroscopy and both dc and grain boundary ionic conductivity increase with Cr content. A high ionic conductivity value of 1.4·10−4 S cm−1 at room temperature and an activation energy of 0.31 eV have been obtained for x = 0.1, which are comparable to those measured in the best ionic conductors reported to date. Photoluminescence and cathodoluminescence spectra indicate that self-trapped excitons and oxygen defects related to the TiO6 octahedra structural units are responsible for the observed luminescence in the visible spectral range, explaining the possible electronic origin of a residual conductivity measured in all the samples. Cr incorporation gives rise to infrared emission bands, attributed to different Cr3+ and Ti3+ intraionic transitions, that may be related to the better grain connectivity achieved by Cr doping.Item A systematic study of Nasicon-type Li1+xMxTi2-x(PO4)3 (M:Cr, Al, Fe) by neutron diffraction and impedance spectroscopy(Solid State Ionics, 2014) Pérez Estébanez, Marta; Isasi Marín, Josefa; Rivera Calzada, Alberto Carlos; Tobbens, Daniel; León Yebra, CarlosA systematic study of Li1+ xMxTi2 − x(PO4)3 with M=Al, Cr and Fe and 0 ≤ x ≤ 1 has been carried out by X-ray and neutron powder diffraction and by impedance spectroscopy. The analysis of the diffraction data allowed us to describe the disposition of the lithium atoms within the structure. They were found to occupy two different positions, the well-known M1 and a new position called M2′. The addition of trivalent metals into the LiTi2(PO4)3 compound, even in small amount, gives rise to the liberation of the M1 sites and simultaneous occupation of the M2′ sites. This situation becomes more pronounced as the substituent content increases, meaning a higher delocalization of lithium atoms within the structure.Moreover, rising temperature also provokes the movement of lithium fromM1 to M2′. The impedance spectroscopy measurements allowed us to relate the electrical properties to the observations of the crystal structure. Both dc bulk and grain boundary ionic conductivity showa thermally activated behavior, and their values increase with substituent content until compositions of x= 0.2–0.3. The activation energy for bulk dc conductivity hardly changes with the substitution, and the main factor affecting the variation of the ionic conductivity is the pre-exponential factor. We find indeed a correlation between the pre-exponential factor and the degree of disorder of the lithium atoms in the structure as determined from neutron diffraction data. The highest conductivity was found in the sample Li1.3Al0.3Ti1.7(PO4)3 with a value of 6.2 × 10−3 S cm−1 at room temperature and activation energy of 0.30 eV, which is comparable with those measured in the best ionic conductors reported to date.Item Structural and cathodoluminiscent properties of Zr0.95Ce0.05O2 nanopowders prepared by sol–gel and template methods(Journal of Luminescence, 2011) Fernández Castillo, Jesús; Isasi Marín, Josefa; Pérez Estébanez, Marta; Aldama, Iván; Arévalo, Pablo; Díaz-Guerra Viejo, CarlosNanopowders of Zr0.95Ce0.05O2 composition have been prepared by a standard Pechini-type sol–gel process and by means of a colloidal crystal template approach. In the latter method, inverse opal Zr0.95Ce0.05O2 powders were fabricated employing poly(methylmethacrylate) (PMMA) colloidal crystals as a template.The effects of the two different synthesis routes on the structure and microstructural characteristics of the prepared nanopowders were evaluated by X-ray diffraction and scanning electron microscopy. For both preparation routes, the X-ray diffraction analysis has shown that a tetragonal fluorite structure is formed with a crystallite size of 35–40 nm. The scanning electron microscopy measurements indicate that the powder obtained by the sol–gel Pechini-type process is comprised of nanoparticles that are arranged in agglomerates with shape and size relatively uniform whereas the inverse opal Zr0.95Ce0.05O2 nanopowders exhibit the formation of macropores with a mean size of 100 nm. The cathodoluminescence spectra of the prepared Zr0.95Ce0.05O2 nanomaterials have been measured in the 300–800 nm wavelength range. The powder prepared by sol–gel method yields a broad emission band centered at 482nm whereas the emission from the inverse opal preparation is considerably less intense.Item Structural, magnetic and luminescent characteristics of Pr3+-doped ZrO2 powders synthesized by a sol–gel method(Journal of Physics D: Applied physics, 2009) Isasi Marín, Josefa; Pérez Estébanez, Marta; Díaz-Guerra Viejo, Carlos; Fernández Castillo, Jesús; Correcher, Virgilio; Cuervo Rodríguez, María RocíoThe structural, magnetic and luminescence properties of praseodymium-doped zirconia powders of compositions Pr0.03Zr0.97O2 and Pr0.05Zr0.95O2 synthesized by a sol–gel process have been investigated. X-ray diffraction patterns indicate that these materials crystallize in a tetragonal fluorite-type structure. Scanning electron microscopy shows that the powders exhibit an agglomerated microcrystalline structure and the grain size may be in the order of 5–20μm. The study of the magnetic properties of these doped metal oxides indicates a Curie–Weiss behaviour in the temperature range (100–300)K that allow us to estimate an effective magnetic moment of 3.51μB, which indicates the presence of Pr3+ in the grown samples. Cathodoluminescence spectra recorded at temperatures between 85 and 295K show emission peaks that can be attributed to transitions between different states within the 4f2 configuration of Pr3+ ions incorporated in the zirconia crystal lattice. Thermoluminescence measured at temperatures ranging from 373 to 773K and at 550 nm wavelength show an intense and broad peak around 653K for the Pr-doped zirconia which is not observed in the undoped material.Item Structural and luminescence characterization of synthetic Cr-doped Ni3(PO4)2(Journal of Physics and Chemistry of solids, 2013) Correcher, Virgilio; Isasi Marín, Josefa; Cubero, Ágata; Pérez Estébanez, Marta; Aldama, Iván; Arévalo, Pablo; Fernández Castillo, Jesús; García Guinea, JavierNi3–xCr2x/3(PO4)2 (x¼0 and 0.02) microcrystalline powders were obtained as single phases via a modified sol–gel Pechini-type in situ polymerizable complex method. The samples were characterized using scanning electron microscopy, X-ray diffraction, cathodoluminescence (CL), and thermoluminescence (TL) techniques. We found that Cr3+ doping modified the average particle and distribution. The mean particle size was 0.441 μm for Ni3(PO4)2 and 0.267 μm for Ni2.98Cr0.013(PO4)2. The results also reveal that Cr3+ doping notably enhanced the CL and TL UV-blue emission.Item Preparation and characterization of Ce0.95Zr0.05O2 nanopowders obtained by solegel and template methods(Materials Chemistry and Physics, 2012) Isasi Marín, Josefa; Pérez Estébanez, Marta; Fernández Castillo, Jesús; Correcher, Virgilio; Aldama, Iván; Arévalo, Pablo; Carbajo, María CarmenCe0.95Zr0.05O2 nanopowders have been prepared by a standard Pechini-type solegel process and by using polymethyl methacrylate (PMMA) colloidal crystals as template. The effects of these different synthesis routes, on the structure and microstructural features of the nanopowders, were evaluated by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and specific surface area measurements. For both preparation routes, the XRD analysis has shown that a cubic fluorite structure is formed with a crystallite size of w45e50 nm. The SEM images indicate that the powder obtained by the solegel Pechini-type process, is constituted by aggregated nanoparticles with relatively uniform shape and size, whereas the powder synthesized as inverse opal exhibits the formation of macropores with a mean size of w130 nm. The specific surface areas of the powder samples obtained by the Pechini-type solegel and inverse opal methods are w56 m2 g 1 and w90 m2 g 1 respectively. Additionally, the thermoluminescence (TL) signal of the synthetized samples has been measured in order to examine its potential application in the field of dosimetry of ionizing radiations.