Structure, Transport and Magnetic properties in La2x_{2x}Sr2−2x_{2-2x}Co2x_{2x}Ru2−2x_{2-2x}O6_{6}

The perovskite solid solutions of the type La$_{2x}$Sr$_{2-2x}$Co$_{2x}$Ru$_{2-2x}$O$_{6}$ with 0.25 $\leq$ x $\leq$ 0.75 have been investigated for their structural, magnetic and transport properties. All the compounds crystallize in double perovskite structure. The magnetization measurements indicate a complex magnetic ground state with strong competition between ferromagnetic and antiferromagnetic interactions. Resistivity of the compounds is in confirmation with hopping conduction behaviour though differences are noted especially for $x$ = 0.4 and 0.6. Most importantly, low field (50Oe) magnetization measurements display negative magnetization during the zero field cooled cycle. X-ray photoelectron spectroscopy measurements indicate presence of Co$^{2+}$/Co$^{3+}$ and Ru$^{4+}$/Ru$^{5+}$ redox couples in all compositions except $x$ = 0.5. Presence of magnetic ions like Ru$^{4+}$ and Co$^{3+}$ gives rise to additional ferromagnetic (Ru-rich) and antiferromagnetic sublattices and also explains the observed negative magnetization.Comment: Accepted for publication in J. Magn. Magn. Mate

Low Temperature Neutron Diffraction Study of MnTe

Investigation of transport and magnetic properties of MnTe at low temperatures sInvestigation of transport and magnetic properties of MnTe at low temperatures showed anomalies like negative coefficient of resistance below 100K and a sharp rise in susceptibility at around 83K similar to a ferromagnetic transition. Low temperature powder neutron diffraction experiments were therefore carried out to understand the underlying phenomena responsible for such anomalous behavior. Our study indicates that the rise in susceptibility at low temperatures is due to strengthening of ferromagnetic interaction within the plane over the inter plane antiferromagnetic interactions.Comment: Appearing in J. Magn. Magn. Mate

X-ray absorption spectra and electronic structure of Haucke-phase-type intermetallic compounds

Les spectres d'absorption K du cobalt dans le métal pur et dans les composés du type RCo5 (où R est une terre rare ou yttrium) ont été observés et mesurés. On trouve dans le cas des composés que les discontinuités principales se déplacent vers les petites énergies par rapport à celle du métal pur ; ceci indique un transfert d'électrons R vers Co. Une courbe tracée entre les déplacements chimiques et les électrons covalents impliqués dans la liaison (calculé en utilisant un formalisme des rayons métalliques d'après Pauling) suggère une corrélation. Cette courbe est employée pour déterminer des électrons covalents du cobalt dans TmCo5 et YCO5 ; des informations utiles concernant la liaison chimique dans ces composés ont été déduites.The K X-ray absorption discontinuity of cobalt in the compounds of the RCo5 family (R = rare earth or yttrium) has been measured with a bent crystal spectrograph. It is observed that the main discontinuity shifts to the low energy side, with respect to that in pure cobalt indicating a flow of charge from R to Co. The plot between the observed shifts and the number of covalently bonded electrons (calculated using a semi-empirical metallic radii formalism due to Pauling) suggests a definite correlation. This plot is then used to obtain the number of covalently bonded electrons of cobalt in TmCo5 and YCo5 for which the self-consistent radii data is not available. Useful conclusions are obtained about chemical bonding in these two compounds

<span style="font-size:11.0pt;font-family: "Times New Roman";mso-fareast-font-family:"Times New Roman";mso-bidi-font-family: Mangal;mso-ansi-language:EN-GB;mso-fareast-language:EN-US;mso-bidi-language: HI" lang="EN-GB">Carbon Nanoparticle Toxicity to marine algae <i style="mso-bidi-font-style: normal">Navicula longa</i> and <i style="mso-bidi-font-style:normal">Isochrysis galbana.</i></span>

331-337Present study reports cytotoxicity of Carbon Nanoparticles to Navicula and Isochrysis. Cytotoxicity was determined by morphological changes, cell density count, Acid Phosphatase and Lactate dehydrogenase assays. Carbon nanoparticles (CNPs) promote concentration as well as exposure dependent toxicity to Navicula & Isochrysis, which exhibited cell death, necrotic changes such as cell shrinkage and pycnosis of nucleus. Lactate Dehydrogenase (LDH) & Acid Phosphatase (ACP) activities elevated significantly, in both algae, in a dose and exposure dependant manner. In Navicula and Isochrysis, LDH activity was elevated by 42.3% and 60.7%, and 44.5% and 90.3%, on exposure to 0.05 mg/mL and 1 mg/mL CNPs for 10 days respectively. Similarly, ACP activity in both Navicula and Isochrysis was elevated by 34.6% and 55.4%, and 11.7% and 18.5%, on exposure to 0.05 mg/mL and 1 mg/mL of CNPs for 10 days respectively, as compared to the controls. The occurrence of tube like structures under the influence of CNPs in algae was also observed

Tailoring a Pt–Ru catalyst for enhanced methanol electro-oxidation

A carbon-supported (1:1) Pt–Ru (Pt–Ru/C) alloy catalyst has been prepared in-house by the sulfito-complex route, and has been tailored to achieve enhanced activity towards methanol electro-oxidation by annealing it at varying temperatures in air. The catalyst samples annealed between 250 and 300 ◦C in air for 30 min exhibit superior catalytic activity towards methanol electro-oxidation in a solid-polymer-electrolyte direct methanol fuel cell (SPE-DMFCs) operating at 90 ◦C. Both the as-prepared and annealed Pt–Ru/C catalysts have been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), and cyclic voltammetry. It is conjectured that while annealing the Pt–Ru/C catalysts, both Pt Pt and Pt Ru bonds increase whereas the Pt O bond shrinks. This is accompanied with a positive variation in Ru/Pt metal ratio suggesting the diffusion of Ru metal from the bulk catalyst to surface with an increase in oxidic ruthenium content. Such a treatment appears seminal for enhancing the electrochemical activity of Pt–Ru catalysts towards methanol oxidation

Methanol steam reforming behavior of sol-gel synthesized nanodimensional CuxFe1-xAl2O4 hercynites

This work reports the outstanding catalytic activity behavior of sol-gel synthesized nanostructured CuxFe1-xAl2O4 (0.3¿=¿x¿=¿0.8; named as CuFeAln, where n¿=¿30, 40, 50, 60, 70 and 80) hercynites towards methanol steam reforming (MSR) for hydrogen generation. Based on the durability studies, we had categorized the higher Cu-doped hercynites (CuFeAl70 and CuFeAl80) as the more effective in regard to activity and stability (maintenance of a methanol conversion of ~80% with low CO selectivity of 2% after 50¿h of continuous operation at 275¿°C for CuFeAl80) when compared with the lower Cu-doped counterparts (CuFeAl30 and CuFeAl40). The specific surface area of all the materials was about 50 m2¿g-1 and they had similar reduction characteristics as obtained from H2-TPR analysis. The lower reducibility below 280¿°C of CuFeAl70 and CuFeAl80 was correlated with the higher stability of these samples during time on stream operation. The powder XRD analyses had shown pure phase hercynite formation with the gradual increase of Cu-doping, while there occurred a phase segregation in the reforming atmosphere leading to the formation of metallic copper. High resolution microstructural analyses had confirmed single phase hercynite formation at nanoscale and a reduction of copper subsequent to ageing as well as certain growth of the copper metal particles (from ~5¿nm to ~8¿nm) corroborating the XRD studies. The surface features from in-situ XPS had also suggested formation of reduced copper species, which was much lower for the higher Cu-doped samples. Cu K edge XANES spectral analyses also pointed to lower occurrence of reduced copper in the aged samples of higher Cu-doped hercynites. The experimental findings had been explained on the basis of partial breakdown of the spinel lattice structure leading to the formation of CuO, followed by its reduction to metallic copper nanocrystallites in the MSR atmosphere. A definite ratio of the reduced to oxidized copper species was maintained with time on stream and this caused nearly stable conversion behavior of the catalysts in methanol steam reforming.Peer Reviewe