Substitution effects on the bulk and surface properties of (Li,Ni)Mn2O4

Manganese oxides of spinel structure, LiMnO, LiNiMnO (0.25 ≤ x≤ 0.75), and NiMnO, were studied by EDS, XRD, SEM, magnetic (M-H, M-T), and XPS measurements. The samples were synthesized by an ultrasound-assisted sol-gel method. EDS analysis showed good agreement with the formulations of the oxides. XRD and Rietveld refinement of X-ray data indicate that all samples crystallize in the Fd3m space group characteristic of the cubic spinel structure. The a-cell parameter ranges from a = 8.2276 Å (x = 0) to a = 8.3980 Å (x = 1). SEM results showed particle agglomerates ranging in size from 2.3 μm (x = 0) down to 0.8 μm (x = 1). Hysteresis magnetization vs. applied field curves in the 5–300K range was recorded. ZFC-FC measurements indicate the presence of two magnetic paramagnetic-ferrimagnetic transitions. The experimental Curie constant was found to vary from 5 to 7.1 cm K mol for the range of compositions studied (0 ≤ x ≤ 1). XPS studies of these oxides revealed the presence of Ni, Mn, and Mn. The experimental Ni/Mn atomic ratios obtained by XPS were in good agreement with the nominal values. A linear relationship of the average oxidation state of Mn with Ni content was observed. The oxide’s cation distributions as a function of Ni content from x = 0 Li[MnMn]O to x = 1 Ni0.352+Mn0.653+[Ni0.652+Mn1.353+]O4 were proposed.Peer Reviewe

In vitro andulafungin susceptibility of 100 of Candida strains obtained previously to the introduction of this echinocandin in Chile Susceptibilidad in vitro a anidulafungina en 100 cepas de especies de Candida aisladas previo a la introducción de esta eq

Fungi, particularly yeasts, have become important opportunistic pathogens that can be resistant to antifungal agents or develop resistance. To address this problem, new molecules such as echinocandins, have been developed. Susceptibility to anidulafungin was studied in yeasts isolated previous to the introduction of this drug in Chile. One hundred strains of different yeast species isolated from invasive fungal infections during 2007 and 2008 were studied. Susceptibility testing of anidulafungin was performed by broth microdilution according to CLSI. All strains were susceptible to anidulafungin. MIC 50 and MIC 90 were 0.125 μg/mL and 1 μg/mL, respectively. Compared to other yeasts, C. parapsilosis showed a slight increase in the MICs for anidulafungin (MIC 50, 1 μg/mL, MIC 90, 2 μg/mL), but remained within the susceptible range. Both, fluconazole resistant (8) and dose dependant susceptible strains (16) were susceptible to anidulafungin. In vitro, this echinocandin appears to be an e

Physical and electrochemical study of cobalt oxide nano- and microparticles

Cobalt oxide nanocrystals of size 17-21 nm were synthesized by a simple reaction between cobalt acetate (II) and dodecylamine. On the other hand, micrometric Co3O4 was prepared using the ceramic method. The structural examination of these materials was performed using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM and HRTEM). XRD studies showed that the oxides were pure, well-crystallized, spinel cubic phases with a-cell parameter of 0.8049 nm and 0.8069 nm for the nano and micro-oxide, respectively. The average particle size was 19 nm (nano-oxide) and 1250 μm (micro-oxide). Morphological studies carried out by SEM and TEM analyses have shown the presence of octahedral particles in both cases. Bulk and surface properties investigated by X-ray photoelectron spectroscopy (XPS), point zero charge (pzc), FTIR and cyclic voltammetry indicated that there were no significant differences in the composition on both materials. The magnetic behavior of the samples was determined using a vibrating sample magnetometer. The compounds showed paramagnetic character and no coercivity and remanence in all cases. Galvanostatic measurements of electrodes formed with nanocrystals showed better performance than those built with micrometric particles. © 2014 Elsevier Inc.Peer Reviewe

Structural and physicochemical properties of nickel manganite NiMn2O4-δsynthesized by sol-gel and ultra sound assisted methods

In this work we present the structural, magnetic and surface characterization of the ceramic nickel manganite oxide NiMnO synthesized by two methods: sol-gel and ultrasound-assisted sol-gel using nitrate salts as precursors. We have characterized the non-stoichiometric samples NiMnO using different physicochemical analyses. X-ray diffraction and Rietveld refinement of the X-ray data indicated that the samples crystallize in the Fd3m space group characteristic of cubic spinel-related oxides. The specific surface area of the oxides was 1.3 m/g (SG) and 16.3 m/g (UASG). SEM results showed particle agglomerates of 1.05 μm (SG) and 0.85 μm (UASG). Temperature dependence magnetization measurements were performed and a ferrimagnetic transition was identified at 103 K and 105 K depending on the preparation method (SG and UASG, respectively). The observed Curie constant was found to vary from 7.4 to 7.7 cm K mol and hysteretic magnetization vs. applied field curves at different temperatures were obtained. XPS studies of these oxides reveal the presence of Ni, Mn, Mn and Mn ions at the surface. A probable ionic distribution as a function of the synthesis method is proposed.Peer Reviewe

Ensemble-based support vector regression with gravitational search algorithm optimization for estimating magnetic relative cooling power of manganite refrigerant in magnetic refrigeration application

Magnetic refrigeration technology (MRT) is considered an energy-efficient and environmental-friendly system of refrigeration that has a considerable potential of replacing the classical gas-compression expansion method of refrigeration. Inclusion of manganite-based material (MBM) in MRT as a magnetic refrigerant has attracted significant attention recently due to cost effectiveness of the refrigerant as well as better resistance to oxidation and corrosion as compared to the commonly used metal gadolinium refrigerant. Relative cooling power (RCP) is one of the most important parameters to be considered while assessing the usefulness of MBM. Its value can be altered through doping with external materials and accurate estimation of the dopant influence is required to achieve the right amount of RCP. This present research work proposes support vector regression (SVR) ensemble models with gravitational search algorithm (GSA) hyper-parameters optimization, for estimating RCP of MBM and to determine the influence of dopants on RCP using ionic radii and dopant concentrations as descriptors. GSA-SVR ensemble model (GSE) is developed by employing the outputs of five different SVR models as descriptors while GSA-SVR ensemble model with averaging (GSEA) uses the average of the five different SVR models as its descriptor. The novel ensemble models outperform other SVR models, specifically; GSE performs better than GSA-SVR model and the conventional SVR model with performance improvement of 269.14% and 283.61%, respectively on the basis of root mean square error (RMSE). Furthermore, GSEA outperforms GSE, GSA-SVR model and conventional SVR with performance improvement of 27.51%, 370.70%, and 389.14%, respectively on the basis of RMSE. The developed GSE and GSEA also perform better than the existing RCP model in the literature with performance improvement of 11.53% and 42.21%, respectively. The results of this research work will not only serve to circumvent the experimental challenges of RCP measurement without loss of experimental precision but also further promotes environment-friendly system of refrigeration