Laura Pascual

Synthesizing nanocrystalline LiMn2O4 by a combustion route

Nanocrystalline samples of lithium manganese oxide with cubic spinel structure have been prepared by combustion of reaction mixtures containing Li(I) and Mn(II) nitrates that operate as oxidisers, and sucrose that acts as fuel. The samples were characterised by X-ray diffraction, transmission electron microscopy, thermal analysis, and impedance and electrochemical measurements. The effect of the fuel content on the purity and morphology of the products was analysed. The samples as prepared showed small amounts of Mn2O3 and Mn3O4 as impurities, depending on the amount of sucrose used in the synthesis. Annealing at 700 °C led to single-phase cubic spinels. In these phases, the smallest average particle size (ca. 30 nm) corresponded to the sample obtained with a hyperstoichiometric amount of fuel. This sample showed the Li1.05Mn1.95O4 composition as deduced from the thermal and electrochemical data. No variation in conductivity associated with the cubic⇔orthorhombic phase transition was observed. The electrochemical behaviour as positive electrode showed good cyclability at high current densities (reversible capacity of 73 mAh g−1 at 2.46 mA cm−2).

Nanosize LiNiyMn2 −yO4(0 < y≤ 0.5) spinels synthesized by a sucrose-aided combustion method. Characterization and electrochemical performance

Nanosize crystalline cathode materials of LiNiyMn2 − yO4 (0 < y ≤ 0.5) composition and spinel-type structure have been obtained by a single-step sucrose-aided self-combustion method. The as-prepared samples contained some amorphous organic impurities that were removed after a short period of heating at 500 °C. The pure single-phase spinels have been characterized by X-ray diffraction, transmission electron microscopy, chemical analysis, and nitrogen sorption isotherms. The samples consist of particles (ca. 24 nm size) that are aggregated in clusters (ca. 1 µm size) in which mesopores (10–80 nm size) appear among the particles. Additional heating at 800° and 1000 °C produces a slight increase in the cubic lattice parameter and a pronounced increase in particle size (>100 nm). Electrical conductivity decreases as the Ni content increases in accordance with an electron hopping mechanism between Mn3+ and Mn4+ ions. The 500 °C- and 800 °C-heated LiNi0.5Mn1.5O4 samples show good electrochemical behaviour at 4.7 V as cathode materials. The capacity (132.7 mA h g−1) found is close to the nominal capacity (146.7 mA h g−1) and remains constant for current densities in the range C/24–2C (where C = 2.6 mA cm−2). At higher current densities (2C–10C) the capacity decreases progressively. The cyclability at the C current density is ca. 99.7% for both samples.

Transparent Oxyfluoride Nano-Glass Ceramics Doped with Pr3+ and Pr3+–Yb3+ for NIR Emission

Pr3+-Yb3+ co-doped oxyfluoride glasses and glass-ceramics (GC) containing LaF3 nanocrystals have been prepared to obtain NIR emission of Yb3+ ions upon Pr3+ excitation in the blue region of the visible spectrum. Two different compositions have been tested 0.1-0.5 Pr-Yb and 0.5-1 Pr-Yb, in addition to Pr3+ singly doped samples. The crystallization mechanism of the nano-glass-ceramics was studied by DTA revealing that it occurs from a constant number of nuclei, the crystal growth being limited by diffusion. HR-TEM demonstrated that phase separation acts as precursor for LaF3 crystallization and a detailed analysis of the chemical composition (EDXS) revealed the enrichment in RE3+ ions inside the initial phase separated droplets, from which the LaF3 crystals are formed. The RE3+ ions incorporation inside LaF3 crystals was also proved by photoluminescence measurements showing Stark splitting of the RE3+ ions energy levels in the glass-ceramic samples. Lifetimes measurements showed the existence of a better energy transfer process between Pr3+ and Yb3+ ions in the glass-ceramics compared to the as made glass, and the highest value of energy transfer efficiency is 59% and the highest theoretical quantum efficiency is 159%, obtained for glass-ceramics GC0.1-0.5 Pr-Yb treated at 620 oC-40 h.

Oxyfluoride glass–ceramic fibers doped with Nd3+: structural and optical characterization

Transparent oxyfluoride glass–ceramic fibers containing LaF3 nanocrystals have been drawn using a single crucible method and crystallization after an appropriate heat treatment. Optical fibers have been obtained a posteriori through the deposition of SiO2 cladding prepared by sol–gel and deposited by dip-coating. Detailed thermal and structural characterization performed by DTA, XRD, HRTEM and SAXS showed the good reproducibility of the technology. Phase separation, due to fluorine immiscibility in an oxide glass matrix, initiates the crystallization. The crystallization mechanism is a diffusion-controlled process and the local compositional changes of the glass matrix around the nanocrystals limit the crystal size to 10–20 nm depending on the treatment conditions. The optical characterization demonstrated the light propagation into the glass–ceramic core and the possibility to selectively excite Nd3+ ions in the fluoride nanocrystals with a corresponding increase of the luminescence efficiency.

Transcriptomic profiling of Melon necrotic spot virus -infected melon plants revealed virus strain and plant cultivar-specific alterations

BackgroundViruses are among the most destructive and difficult to control plant pathogens. Melon (Cucumis melo L.) has become the model species for the agriculturally important Cucurbitaceae family. Approaches that take advantage of recently developed genomic tools in melon have been extremely useful for understanding viral pathogenesis and can contribute to the identification of target genes for breeding new resistant cultivars. In this work, we have used a recently described melon microarray for transcriptome profiling of two melon cultivars infected with two strains of Melon necrotic spot virus (MNSV) that only differ on their 3′-untranslated regions.ResultsMelon plant tissues from the cultivars Tendral or Planters Jumbo were locally infected with either MNSV-Mα5 or MNSV-Mα5/3’264 and analysed in a time-course experiment. Principal component and hierarchical clustering analyses identified treatment (healthy vs. infected) and sampling date (3 vs. 5 dpi) as the primary and secondary variables, respectively. Out of 7566 and 7074 genes deregulated by MNSV-Mα5 and MNSV-Mα5/3’264, 1851 and 1356, respectively, were strain-specific. Likewise, MNSV-Mα5/3’264 specifically deregulated 2925 and 1618 genes in Tendral and Planters Jumbo, respectively. The GO categories that were significantly affected were clearly different for the different virus/host combinations. Grouping genes according to their patterns of expression allowed for the identification of two groups that were specifically deregulated by MNSV-Mα5/3’264 with respect to MNSV-Mα5 in Tendral, and one group that was antagonistically regulated in Planters Jumbo vs. Tendral after MNSV-Mα5/3’264 infection. Genes in these three groups belonged to diverse functional classes, and no obvious regulatory commonalities were identified. When data on MNSV-Mα5/Tendral infections were compared to equivalent data on cucumber mosaic virus or watermelon mosaic virus infections, cytokinin-O-glucosyltransferase2 was identified as the only gene that was deregulated by all three viruses, with infection dynamics correlating with the amplitude of transcriptome remodeling.ConclusionsStrain-specific changes, as well as cultivar-specific changes, were identified by profiling the transcriptomes of plants from two melon cultivars infected with two MNSV strains. No obvious regulatory features shared among deregulated genes have been identified, pointing toward regulation through differential functional pathways.

Transparent SiO2-GdF3 sol–gel nano-glass ceramics for optical applications

AbstractTransparent oxyfluoride nano-glass-ceramics (GCs) containing GdF3 nanocrystals undoped and doped with 0.5 Eu3+ (mol%) were obtained by a novel sol–gel method after sintering at temperatures such low as 550 °C. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) show the precipitation of GdF3 nanocrystals with size between 7 and 10 nm, depending on the crystalline phase (hexagonal or orthorhombic) and the heating time. Fourier transform infrared spectroscopy (FTIR) analysis allows following the system evolution during the heat treatment showing the decomposition of trifluoroacetic acid (TFA), used as fluorine precursor, together with the formation of fluoride lattice bonding. Energy dispersive X-ray (EDX) analysis confirms the incorporation of the RE ions in the fluoride nanocrystals in the GCs. The ions incorporation on the GdF3 crystals is also supported by optical characterisation. Photoluminescence measurements result in a well resolved structure together with a narrowing of the Eu3+ emission and excitation spectra in the GCs compared to the xerogel. Moreover, the asymmetry ratio between the electric dipole transition (5D0→7F2) to the magnetic dipole transition (5D0→7F1) is reduced in GCs, indicating that Eu3+ ions are incorporated in the GdF3 crystalline phases. Moreover, Gd3+→Eu3+ energy transfer with enhancement of the energy transfer efficiency was observed in the GCs, further supported by fluorescence decay curves. HighlightsEu3+ doped SiO2-GdF3 GCs with 20 mol% of crystalline phase has been successfully obtained by sol–gel method.The use of methyl triethoxysilane allows obtaining crack-free GCs samples and reduces the hydroxyl groups.Energy transfer with enhancement of efficiency was observed from Gd3+ to Eu3+ in the nanocrystals.