Pulsed versus DC I-V characteristics of resistive manganites

We report on pulsed and DC I-V characteristics of polycrystalline samples of three charge-ordered manganites, Pr_{2/3}Ca_{1/3}MnO_3, Pr_{1/2}Ca_{1/2}MnO_3, Bi_{1/2}Sr_{1/2}MnO_3 and of a double-perovskite Sr_2MnReO_6, in a temperature range where their ohmic resistivity obeys the Efros-Shklovskii variable range hopping relation. For all samples, the DC I(V) exhibits at high currents negative differential resistance and hysteresis, which mask a perfectly ohmic or a moderately nonohmic conductivity obtained by pulsed measurements. This demonstrates that the widely used DC I-V measurements are usually misleading.Comment: 6 pages, 4 figures. Accepted for publication to AP

Inter-grain tunneling in the half-metallic double-perovskites Sr2_2BB'O6_6 (BB'-- FeMo, FeRe, CrMo, CrW, CrRe

The zero-field conductivities ($\sigma$) of the polycrystaline title materials, are governed by inter-grain transport. In the majority of cases their $\sigma$(T) can be described by the "fluctuation induced tunneling" model. Analysis of the results in terms of this model reveals two remarkable features: 1. For \emph{all} Sr$_2$FeMoO$_6$ samples of various microstructures, the tunneling constant (barrier width $\times$ inverse decay-length of the wave-function) is $\sim$ 2, indicating the existence of an intrinsic insulating boundary layer with a well defined electronic (and magnetic) structure. 2. The tunneling constant for \emph{all} cold-pressed samples decreases linearly with increasing magnetic-moment/formula-unit.Comment: 10 pages, 2 tables, 3 figure

Selective photocatalytic CO2_2 reduction in water through anchoring of a molecular Ni catalyst on CdS nanocrystals

Photocatalytic conversion of CO$_2$ into carbonaceous feedstock chemicals is a promising strategy to mitigate greenhouse gas emissions and simultaneously store solar energy in chemical form. Photocatalysts for this transformation are typically based on precious metals and operate in nonaqueous solvents to suppress competing H$_2$ generation. In this work, we demonstrate selective visible-light-driven CO$_2$ reduction in water using a synthetic photocatalyst system that is entirely free of precious metals. We present a series of self-assembled nickel terpyridine complexes as electrocatalysts for the reduction of CO$_2$ to CO in organic media. Immobilization on CdS quantum dots allows these catalysts to be active in purely aqueous solution and photocatalytically reduce CO$_2$ with >90% selectivity under UV-filtered simulated solar light irradiation (AM 1.5G, 100 mW cm$^{–2}$, λ > 400 nm, pH 6.7, 25 °C). Correlation between catalyst immobilization efficiency and product selectivity shows that anchoring the molecular catalyst on the semiconductor surface is key in controlling the selectivity for CO$_2$ reduction over H$_2$ evolution in aqueous solution.Christian Doppler Research Association, OMV group, Isaac Newton Trust, the German Research Foundation, the World Premier International Research Center Initiative, MEXT, Japa

Plasmonic enhancement in BiVO4 photonic crystals for efficient water splitting.

Photo-electrochemical water splitting is a very promising and environmentally friendly route for the conversion of solar energy into hydrogen. However, the solar-to-H2 conversion efficiency is still very low due to rapid bulk recombination of charge carriers. Here, a photonic nano-architecture is developed to improve charge carrier generation and separation by manipulating and confining light absorption in a visible-light-active photoanode constructed from BiVO4 photonic crystal and plasmonic nanostructures. Synergistic effects of photonic crystal stop bands and plasmonic absorption are observed to operate in this photonic nanostructure. Within the scaffold of an inverse opal photonic crystal, the surface plasmon resonance is significantly enhanced by the photonic Bragg resonance. Nanophotonic photoanodes show AM 1.5 photocurrent densities of 3.1 ± 0.1 mA cm(-2) at 1.23 V versus RHE, which is among the highest for oxide-based photoanodes and over 4 times higher than the unstructured planar photoanode.UK Engineering and Physical Science Research Council. Grant Numbers: EP/H00338X/2, EP/G060649/1 European Community's Seventh Framework Programme. Grant Number: FP7/2007–2013 CARINHYPH project. Grant Number: 310184 Minstry of Science and Technology of Taiwan. Grant Number: 102-2218-E-006-014-MY2 Christian Doppler Research Association OMV Group, a Marie Curie Intra-European Fellowship. Grant Number: FP7-PEOPLE-2011-IEF 298012 ERC. Grant Number: 320503This is the final published version currently under embargo. This will be updated once the publisher has granted a CC BY license

A simple approach to the correlation of rotovibrational states in four-atomic molecules

The problem of correlation between quantum states of four-atomic molecules in different geometrical configurations is reviewed in detail. A general, still simple rule is obtained which allows one to correlate states of a linear four-atomic molecule with those of any kind of non-linear four-atomic molecule.Comment: 16 pages (+8 figures), Postscript (ready to print!

A Tool to Recover Scalar Time-Delay Systems from Experimental Time Series

We propose a method that is able to analyze chaotic time series, gained from exp erimental data. The method allows to identify scalar time-delay systems. If the dynamics of the system under investigation is governed by a scalar time-delay differential equation of the form $dy(t)/dt = h(y(t),y(t-\tau_0))$, the delay time $\tau_0$ and the functi on $h$ can be recovered. There are no restrictions to the dimensionality of the chaotic attractor. The method turns out to be insensitive to noise. We successfully apply the method to various time series taken from a computer experiment and two different electronic oscillators

Dichlorido[μ-10,21-dimethyl-2,7,13,18-tetra­phenyl-3,6,14,17-tetra­aza­tricyclo­[17.3.1.18,12]tetra­cosa-1(23),2,6,8,10,12(24),13,17,19,21-deca­ene-23,24-diolato]dicopper(II) ethanol hemisolvate dihydrate

The dinuclear title complex, [Cu2(C46H38N4O2)Cl2]·0.5C2H5OH·2H2O, is located on crystallographic inversion centres with two half-mol­ecules in the asymmetric unit. The two CuII atoms are coordinated by a hexa­dentate dianionic ligand formed in situ from the condensation of two tridentate ligands by four imine N atoms and two bridging phenolate O atoms along with two Cl atoms at axial positions. The coordination geometry around the metal atoms is distorted square-pyramidal (τ = 0.185 and 0.199). The non-bonding Cu⋯Cu distances are 2.9556 (12) and 2.9506 (12) Å in the two dimers. The packing is stabilized through solvent-mediated inter­molecular O—H⋯O and O—H⋯Cl hydrogen bonds. The diamine chain of one of the dimers is disordered over two positions in a 0.680 (5):0.320 (5) ratio