Raman spectroscopy in Zinc Ferrites Nanoparticles

ZnFe2O4 ferrite nanoparticles are arousing a great interest in the biomedical field, thanks to their superparamagnetic behavior at room temperature. Functional properties depend on composition, size, nanoparticle architecture and, in turn, on the synthesis methods. Bulk ZnFe2O4 has the normal spinel structure (all Zn2+ ions in tetrahedral and all Fe3+ ions in octahedral positions), but at the nanometric size inversion takes place with a cationic mixing on divalent and trivalent sites. The sensitivity of the Raman probe to cation disorder favored the appearance of several works on a rich variety of nanosized zinc ferrites. An overview on these results is reported and discussed at variance with synthesis methods, grain dimensions, and dopants. We add to this landscape our results from new nanosized powder samples made by microwave-assisted combustion, with different dopants (Ca, Sr on Zn site and Al, Gd on Fe site). A detailed analysis of A1g, Eg, 3F2g Raman modes has been performed and Raman band parameters have been derived from best-fitting procedures and carefully compared to literature data. The vibrational results are discussed taking into account the characterization from X-ray powder diffraction raction, SEM-EDS probe, EPR spectroscopy and, of course, the magnetic responses

Role of non-magnetic dopants (Ca, Mg) in GdFeO 3 perovskite nanoparticles obtained by different synthetic methods: structural, morphological and magnetic properties

AbstractGdFeO3 perovskite attracted large interest in different fields thanks to peculiar magnetic and optical properties that are further tunable by means of doping processes and achievable on both Gd and Fe sites or by properly choosing the synthesis routes. In this paper, nanometric GdFeO3 compounds, undoped and doped with diamagnetic Ca2+ and Mg2+ ions, were synthesized by microwave assisted, sol–gel, and polyol syntheses and characterized by X-ray diffraction, showing solid solutions formation. Raman spectroscopy allowed us to confirm, from peak enlargements, the Ca and Mg substitution on Gd and Fe sites, respectively. The magnetic data showed the presence of magnetic domains as consequence of doping with diamagnetic ions, which seem to play a crucial role in the magnetic activity of the compounds. A superparamagnetic behaviour is evidenced; nevertheless, its intrinsic character is not definitely demonstrated. Indeed, the possible presence of traces of magnetic impurities, which are easily obtainable in these samples, such as iron oxides, must be taken into account

Do sample preparation techniques affect the relative abundance of Florisphaera profunda?

none6siWe investigated which method among smearing, settling, filtration, and random settling is the most accurate for determining the relative abundance of Florisphaera profunda. This species is included in paleoproductivity indices because it is one of the most important deep-water dwellers. Therefore, an accurate assessment of its relative abundance is key to monitoring variations in thermocline and nutricline depths. The low birefringence and flat polygonal shape of F. profunda may lead to inaccurate estimates of its relative abundance as it is poorly visible under light microscopy (LM), and different sample preparation may affect the number of specimens on each slide. We studied eight samples from the Ocean Drilling Program (ODP) Site 1209B (Shatsky Rise, NW Pacific) from the last 450 kyr. Each sample was prepared five times using each technique for a total of 160 slides. Through a rigorous analytical and statistical approach, we demonstrated the high reproducibility of each method and showed good agreement among techniques at low percentages of F. profunda. When the percentage of this species increases, the random settling technique differs from the others. Filtration and random settling preparation techniques were calibrated by spiking samples with microbeads. The ratio of microbeads observed in slides prepared using these two methods reflects bias due to loss of particles in the filtration technique. In addition, a hydrodynamic model for a fluttering and tumbling plate – such as F. profunda nannoliths – is proposed here along with calculated sinking velocities. These findings confirmed the efficiency of the long decantation time proposed for the random settling technique. The analysis of replicates, the validation with microbeads and the estimation of settling velocity of nannofossils in the tube convinced us that the higher relative abundance recorded by the random technique is not due to an imprecision of this method but, on the contrary, reflects the fact that it is more effective.openLupi, Claudia; Bordiga, Manuela; Sacchi, Roberto; Galinetto, Pietro; Beaufort, Luc; Cobianchi, MiriamLupi, Claudia; Bordiga, Manuela; Sacchi, Roberto; Galinetto, Pietro; Beaufort, Luc; Cobianchi, Miria

Micro-Raman Spectroscopy of Dental Implants Subjected to Different Surface Treatments

The aim of the study was to qualitatively investigate the structure of the surface layer of TiO2 on dental implants made of Ti-6Al-4V subjected to different manufacturing treatments. M (machined), B (Al2O3-blasted), E (HNO3HF-etched), B + E and A (B + E + anodized) implants and a further group receiving the same treatments as the first group with the addition of a final decontamination with cold plasma were included in the study. Examination was performed using micro-Raman spectroscopy. The surface treatments evaluated did not achieve the formation of crystalline TiO2. The increase in the complexity of surface treatment produced a proportional increase in the thickness of amorphous TiO2 oxide. In the B + E group, the plasma treatment enhanced the amorphous oxide thickness of TiO2. The other surfaces treated by plasma decontamination did not show a difference to the respective untreated ones. The investigated surface treatments did not change the crystalline cage of TiO2 in Ti-6Al-4V implants but affected the thickness of the oxide layer. The biological response could be influenced by different oxide thicknesses. Additional information on superficial TiO2 structural organization can be obtained by micro-Raman evaluation of dental implants. Dental implants with B + E + plasma and A superficial treatments allowed the maximum formation of the amorphous oxide thickness

Strong enhancement of d-wave superconducting state in the three-band Hubbard model coupled to an apical oxygen phonon

We study the hole binding energy and pairing correlations in the three-band Hubbard model coupled to an apical oxygen phonon, by exact diagonalization and constrained-path Monte Carlo simulations. In the physically relevant charge-transfer regime, we find that the hole binding energy is strongly enhanced by the electron-phonon interaction, which is due to a novel potential-energy-driven pairing mechanism involving reduction of both electronic potential energy and phonon related energy. The enhancement of hole binding energy, in combination with a phonon-induced increase of quasiparticle weight, leads to a dramatic enhancement of the long-range part of d-wave pairing correlations. Our results indicate that the apical oxygen phonon plays a significant role in the superconductivity of high-$T_c$ cuprates.Comment: 5 pages, 5 figure

Structural, spectroscopic and magnetic investigation of the LiFe1-xMnxPO4 (x = 0 - 0.18) solid solution

Different solid state and sol-gel preparations of undoped and Mn substituted cathode material LiFePO4 are investigated. Li3PO4, Fe2P2O7 and Li4P2O7 are detected and quantified by XRPD only in solid state synthesis. In addition, micro-Raman spectra reveal low amount of different iron oxides clusters. EPR data, combined with the results of magnetization measurements, evidence signals from Fe3+ ions in maghemite nanoclusters, and in Li3Fe2(PO4)3. The sol–gel synthesis, showing the lowest amount of impurity phases, seems the most suitable to obtain a promising cathode material. The structural refinement gives new insights into the cation distribution of the Mn doped triphylite structure: (i) about 85% of Mn2+ ions substitutes Fe2+, the remaining 15% being located on the Li site, thus suggesting a structural disorder also confirmed by EPR and micro-Raman results; (ii) Mn ions on the Li site are responsible for the observed slight cell volume expansion

Cr and Ni doping of Li4Ti5O12: cation distribution and functional properties

Cr- and Ni-doped Li4Ti5O12 compound has been characterized through the combined use of X-ray powder diffraction, electron paramagnetic resonance (EPR), 7Li nuclear magnetic resonance magic-angle spinning (NMR-MAS), micro-Raman, and magnetization measurements. The doping, occurring on the octahedral site of the cubic Li4Ti5O12 spinel lattice, strongly affects both the local and the average structural properties. The glassy character of the observed EPR signals suggests structural disorder in the stable Li4Ti5O12 matrix and the presence of clustering phenomena or nonhomogeneous distribution of the dopant ion, as also supported by 7Li NMR-MAS, micro-Raman, and magnetization results. The computation by numerical method of the complex EPR signal of the Cr-doped sample suggests that both CrTi and CrLi substitutions occur, giving rise to two distinct EPR components, corresponding to opposite axial distortion of the relative octahedral environments. On the basis of the compositional data, defect models involving oxygen or cation vacancies are proposed to explain the conductivity of the doped material

Influence of composition on the electro-optic coefficients of Mg-doped lithium niobate

the EO coefficients r33, r13 and rc of Magnesium doped Lithium Niobate crystals are measured in the wavelength range 532-1550 nm and compared to the ones of pure congruent and stoichiometric Lithium Niobate. Magnesium is among the most effective doping ions for improving the photorefractive damage resistance of Lithium Niobate. The exploitation of the outstanding EO properties of Magnesium doped Lithium Niobate at high power levels are foreseen

Optical Properties of Cubic Stabilized Zirconia

Optical absorption across the fundamental edge and the associated photoluminescence, have been studied in single crystals of yttrium stabilized zirconia (YSZ) of varying yttrium concentration. The results allow discrimination of a region of intrinsic transitions (above 5.2 eV) from a low energy region, where disorder-induced transitions are dominating. The size of extra absorption in this range shows an inverse correlation to the stoichiometric ratio, to be interpreted in terms of progressive ordering of the vacancy system