High quality thin films of thermoelectric misfit cobalt oxides prepared by a chemical solution method

Misfit cobaltates ([Bi/Ba/Sr/Ca/CoO]nRS[CoO2]q) constitute the most promising family of thermoelectric oxides for high temperature energy harvesting. However, their complex structure and chemical composition makes extremely challenging their deposition by high-vacuum physical techniques. Therefore, many of them have not been prepared as thin films until now. Here we report the synthesis of high-quality epitaxial thin films of the most representative members of this family of compounds by a water-based chemical solution deposition method. The films show an exceptional crystalline quality, with an electrical conductivity and thermopower comparable to single crystals. These properties are linked to the epitaxial matching of the rock-salt layers of the structure to the substrate, producing clean interfaces free of amorphous phases. This is an important step forward for the integration of these materials with complementary n-type thermoelectric oxides in multilayer nanostructuresThis research was supported by the European Research Council (ERC StG-2DTHERMS), Ministerio de Economía y Competitividad of Spain (MAT2010-16157 & MAT2013-44673-R) and Xunta de Galicia (2012-CP071). J.M.V-F acknowledges the MINECO for support with a PhD grant of the FPI programS

Magnetically induced CO2 methanation using exchange‐coupled spinel ferrites in cuboctahedron‐shaped nanocrystals

Magnetically induced catalysis can be promoted taking advantage of optimal heating properties from the magnetic nanoparticles to be employed. However, when unprotected, these heating agents that are usually air-sensitive, get sintered under the harsh catalytic conditions. In this context, we present, to the best of our knowledge, the first example of air-stable magnetic nanoparticles that: 1) show excellent performance as heating agents in the CO2 methanation catalyzed by Ni/SiRAlOx, with CH4 yields above 95 %, and 2) do not sinter under reaction conditions. To attain both characteristics we demonstrate, first the exchange-coupled magnetic approach as an alternative and effective way to tune the magnetic response and heating efficiency, and second, the chemical stability of cuboctahedron-shaped core–shell hard CoFe2O4–soft Fe3O4 nanoparticles.Xunta de Galicia | Ref. IN607 A 2018/5Xunta de Galicia | Ref. ED431C 2016-034Agencia Estatal de Investigación | Ref. CTM2017-84050-

Low-temperature spin excitations in frustrated ZnCr2O4 probed by high-field thermal conductivity

The magnetoelastic excitations of spin frustrated ZnCr2O4 are studied by the magnetic field dependence of the thermal conductivity k down to 50 mK. Above the first-order magnetostructural transition at TN,S≈ 12.5 K, spin fluctuations are strongly coupled to acoustic phonons, leading to a glasslike dependence of k(T), up to Θ CW. In the symmetry broken phase below TN,S, k shows a dominant magnetic contribution even at the lowest temperatures probed in this work. Application of a magnetic field above 2.5 T destabilizes the spin-bond structure, leading to a sudden increase and a nonconventional temperature dependence of the thermal conductivity. The possibility of the coexistence of gapped and gapless excitations in this magnetic phase is discussedThis work was partially supported by MAT2010-16157 (Ministerio de Economía y Competitividad, Spain) and by the DFG via TRR 80 (Augsburg-Munich). Z.Y.Z. and X.F.S. acknowledge support from the National Natural Science Foundation of China, the National Basic Research Program of China (Grant Nos. 2009CB929502 and 2011CBA00111), and the Fundamental Research Funds for the Central Universities (Program No. WK2340000035). V.Z. acknowledges Los Alamos National Lab Directed Research Project 2010000043DRS

In vitro study of the therapeutic potential of brown crude fucoidans in osteoarthritis treatment

[Abstract] Osteoarthritis, one of the most common joint degenerative pathologies, still has no cure, and current treatments, such as nonsteroidal anti-inflammatory drugs, can cause serious adverse effects when taken for a long time. Brown seaweed crude fucoidans are used for the clinical treatment of several pathologies. In this study, the therapeutical potential of these biocompounds was analyzed in primary chondrocytes and the 260TT human chondrocyte cell line. Crude fucoidan from Undaria pinnatifida (Up) and Sargassum muticum (Sm) was obtained by different extraction techniques (microwave-assisted extraction, pressurized hot-water extraction, ultrasound-assisted extraction) and chemically and structurally characterized by Fourier transform infrared spectroscopy, high-performance size-exclusion chromatography, proton nuclear magnetic resonance, and scanning electron microscopy. Once cell viability was confirmed in chondrocytes treated with crude fucoidans, we evaluated their anti-inflammatory effects, observing a significant reduction in IL-6 production stimulated by IL-1β. Findings were confirmed by analysis of IL-6 and IL-8 gene expression, although only fucoidans from Up achieved a statistically significant reduction. Besides this, the antioxidant capacity of crude fucoidans was observed through the upregulation of Nrf-2 levels and the expression of its transcriptional target genes HO-1 and SOD-2, with compounds from Up again showing a more consistent effect. However, no evidence was found that crude fucoidans modulate senescence, as they failed to reduced β-galactosidase activity, cell proliferation, or IL-6 production in chondrocytes stimulated with etoposide. Thus, the findings of this research seem to indicate that the tested crude fucoidans are capable of partially alleviating OA-associated inflammation and oxidative stress, but fail to attenuate chondrocyte senescence

Apparent auxetic to non-auxetic crossover driven by Co2+ redistribution in CoFe2O4 thin films

Oxide spinels of general formula AB2O4 (A = Mg2+, Fe2+; B = Al3+, Cr3+, etc.) constitute one of the most abundant crystalline structures in mineralogy. In this structure, cations distribute among octahedral and tetrahedral sites, according to their size and the crystal-field stabilization energy. The cationic arrangement determines the mechanical, magnetic, and transport properties of the spinel and can be influenced by external parameters like temperature, pressure, or epitaxial stress in the case of thin films. Here, we report a progressive change in the sign of the Poisson ratio, ν, in thin films of CoFe2O4, defining a smooth crossover from auxetic (ν 0) behavior in response to epitaxial stress and temperature. Microstructural and magnetization studies, as well as ab initio calculations, demonstrate that such unusual elastic response is actually due to a progressive redistribution of Co2+ among the octahedral and tetrahedral sites of the spinel structure. The results presented in this work clarify a long standing controversy about the magnetic and elastic properties of Co-ferrites and are of general applicability for understanding the stress-relaxation mechanism in complex crystalline structures.This work has received financial support from Ministerio de Economía y Competitividad (Spain) under Project No. MAT2016-80762-R and MAT2017-82970-C2-R, Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2016-2019, No. ED431G/09), the European Union (European Regional Development Fund-ERDF), and the European Commission through the Horizon H2020 funding by H2020-MSCA-RISE-2016-Project No. 734187–SPICOLOST. I.L.d.P. and B.R.-M. thank the funding under the ESTEEM2 project and the researchers L.A. Rodríguez and E. Snoeck for preliminary Lorentz Microscopy (L.M.) and electron holography (EH) studies in CoFe2O4 samples synthesized by PAD method performed at CEMES (Toulouse)S

‘Costa da Morte’ ataxia is spinocerebellar ataxia 36: clinical and genetic characterization

Spinocerebellar ataxia 36 has been recently described in Japanese families as a new type of spinocerebellar ataxia with motor neuron signs. It is caused by a GGCCTG repeat expansion in intron 1 of NOP56. Family interview and document research allowed us to reconstruct two extensive, multigenerational kindreds stemming from the same village (Costa da Morte in Galicia, Spain), in the 17th century. We found the presence of the spinocerebellar ataxia 36 mutation co-segregating with disease in these families in whom we had previously identified an ∼0.8 Mb linkage region to chromosome 20 p. Subsequent screening revealed the NOP56 expansion in eight additional Galician ataxia kindreds. While normal alleles contain 5–14 hexanucleotide repeats, expanded alleles range from ∼650 to 2500 repeats, within a shared haplotype. Further expansion of repeat size was frequent, especially upon paternal transmission, while instances of allele contraction were observed in maternal transmissions. We found a total of 63 individuals carrying the mutation, 44 of whom were confirmed to be clinically affected; over 400 people are at risk. We describe here the detailed clinical picture, consisting of a late-onset, slowly progressive cerebellar syndrome with variable eye movement abnormalities and sensorineural hearing loss. There were signs of denervation in the tongue, as well as mild pyramidal signs, but otherwise no signs of classical amyotrophic lateral sclerosis. Magnetic resonance imaging findings were consistent with the clinical course, showing atrophy of the cerebellar vermis in initial stages, later evolving to a pattern of olivo-ponto-cerebellar atrophy. We estimated the origin of the founder mutation in Galicia to have occurred ∼1275 years ago. Out of 160 Galician families with spinocerebellar ataxia, 10 (6.3%) were found to have spinocerebellar ataxia 36, while 15 (9.4%) showed other of the routinely tested dominant spinocerebellar ataxia types. Spinocerebellar ataxia 36 is thus, so far, the most frequent dominant spinocerebellar ataxia in this region, which may have implications for American countries associated with traditional Spanish emigration

Grain boundary effects in bulk colossal magneto resistive (CMR) manganites and manganite/insulator composites: electrical and magnetic properties

peer reviewedIn the first part of this paper, we discuss the effects of grain boundaries on the properties of bulk colossal magnetoresistive (CMR) manganites We compare the electrical resistivity and AC magnetic susceptibility of perovskite La-Ca-Mn-O samples with the same nominal stoichiometry but differing in their microstructure (i) a single grain sample, (ii) a sample containing two grains and (iii) a polycrystalline sample Emphasis is placed on information that can be deduced from the measurements in each case In the second part of the paper, we report the data measured on composite samples containing a CMR phase (La-Ca-Mn-O) and an insulating phase (Mn3O4) The results are discussed in the framework of percolation theory We show how the grain boundaries affect the electrical properties of these materials, and we highlight the crucial role of geometric (demagnetization) effects on the resistance vs magnetic field measurement

Improvement of the thermoelectric properties of [Bi1.68Ca2O4-delta](RS)[CoO2](1.69) cobaltite by chimie douce methods

[Bi1 68Ca2O4 delta](RS)[CoO2](1 69) has been obtained by different chimie douce methods and uniaxially or isostatically pressed The influence of these parameters on the thermoelectric properties has been investigated. Contrary to the Seebeck coefficient, which remains unchanged, the electrical conductivity is greatly modified In particular, spray-drying synthesis followed by uniaxial pressing results in an electrical conductivity two times larger than in the case of conventional solid state synthesis. Our results suggest that a narrow particle size distribution is beneficial to the thermoelectric properties of the layered compounds. The spray-drying technique seems to be promising to Improve the electrical conductivity of layered materials. Moreover, this method presents other advantages (homogeneous samples and less energetic processing) which could be interesting to the future manufacturing of thermoelectric devices (C) 2010 Elsevier Inc. All rights reservedChema

Unraveling the multi-featured magnetic behavior of Nd0.75Sr0.25CoO3 perovskite nanocrystals annealed at different temperatures

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGPerovskite nanocrystals are gaining increased attention because of their magnetic, transport and catalytic properties, and particularly there is a renewable interest of cobalt perovskites for catalysis. Accordingly, the correct interpretation of their properties stemming from a particular configuration of the cations within this crystalline structure is compulsory. Herein, we report the synthesis of Nd0.75Sr0.25CoO3 nanocrystals using the citrate sol-gel method and annealed at different final temperatures (600 °C, 700 °C, 800 °C and 1150 °C). Their characterization was carried out combining transmission electron microscopy, X-ray diffraction, Raman spectroscopy and vibrating sample magnetometry, demonstrating their complementarity to get the whole picture of the multi-featured perovskite-based nanocrystal behavior.Xunta de Galicia | Ref. ED431C 2016-034Ministerio de Economía y Competitividad | Ref. CTM2017-84050-