Erratum: Lattice Dynamics Coupled to Charge and Spin Degrees of Freedom in the Molecular Dimer-Mott Insulator κ-(BEDT-TTF)_{2}Cu[N(CN)_{2}]Cl [Phys. Rev. Lett. 123, 027601 (2019)].

This corrects the article DOI: 10.1103/PhysRevLett.123.027601.

Insight into Design of Improved Oxide Ion Conductors: Dynamics and Conduction Mechanisms in the Bi0.913V0.087O1.587 Solid Electrolyte.

Extensive quasielastic neutron scattering measurements have been used to directly observe oxide ion dynamics on the nanosecond time scale in bismuth vanadate with formula Bi0.913V0.087O1.587, which exhibits remarkable oxide ion conductivity at low temperatures. This is the longest time scale neutron scattering study of any fluorite-type solid electrolyte, and it represents only the second case of oxide ion dynamics in any material observed on a nanosecond time scale by quasielastic neutron scattering. Ab initio molecular dynamics simulations reveal two mechanisms that contribute to the oxide ion dynamics in the material: a slower diffusion process through the Bi-O sublattice and a faster process which corresponds to more localized dynamics of the oxide ions within the VO x coordination spheres. The length of the trajectories simulated and the validation of the simulations by neutron scattering experiments provide for the first time a quantitative insight into the relative contributions of the two processes to the oxide ion conduction in this exceptional solid electrolyte, which can be used to derive design principles for the preparation of related oxide ion conductors with even better properties.

Lattice Dynamics Coupled to Charge and Spin Degrees of Freedom in the Molecular Dimer-Mott Insulator κ-(BEDT-TTF)_{2}Cu[N(CN)_{2}]Cl.

Inelastic neutron scattering measurements on the molecular dimer-Mott insulator κ-(BEDT-TTF)_{2}Cu[N(CN)_{2}]Cl reveal a phonon anomaly in a wide temperature range. Starting from T_{ins}∼50-60 K where the charge gap opens, the low-lying optical phonon modes become overdamped upon cooling towards the antiferromagnetic ordering temperature T_{N}=27 K, where also a ferroelectric ordering at T_{FE}≈T_{N} occurs. Conversely, the phonon damping becomes small again when spins and charges are ordered below T_{N}, while no change of the lattice symmetry is observed across T_{N} in neutron diffraction measurements. We assign the phonon anomalies to structural fluctuations coupled to charge and spin degrees of freedom in the BEDT-TTF molecules.

µ-EXAFS, µ-XRF, and µ-PL characterization of a multi-quantum-well electroabsorption modulated laser realized via selective area growth.

In the past few years, strong efforts have been devoted to improving the frequency of optical-fiber communications. In particular, the use of a special kind of integrated optoelectronic device called an electroabsorption modulated laser (EML) allows communication at 10 Gb s(-1) or higher over long propagation spans (up to 80 km). Such devices are realized using the selective area growth (SAG) technique and are based on a multiple quantum well (MQW) distributed-feedback laser (DFB) monolithically integrated with a MQW electroabsorption modulator (EAM). Since the variation in the chemical composition between these two structures takes place on the micrometer scale, in order to study the spatial variation of the relevant parameters of the MQW EML structures, the X-ray microbeam available at the ESRF ID22 beamline is used. The effectiveness of the SAG technique in modulating the chemical composition of the quaternary alloy is proven by a micrometer-resolved X-ray fluorescence (µ-XRF) map. Here, reported micrometer-resolved extended X-ray absorption fine structure (µ-EXAFS) spectra represent the state of the art of µ-EXAFS achievable at third-generation synchrotron radiation sources. The results are in qualitative agreement with X-ray diffraction (XRD) and micrometer-resolved photoluminescence (µ-PL) data, but a technical improvement is still crucial in order to make µ-EXAFS really quantitative on such complex heterostructures.

Preparation of supported Pd catalysts: from the Pd precursor solution to the deposited Pd2+ phase.

The preparation by the deposition-precipitation method (using Na(2)PdCl(4) as a palladium precursor and Na(2)CO(3) as a basic agent) of Pd catalysts supported on gamma-Al(2)O(3) and on two different types of active carbons has been followed by several techniques (UV-vis, EXAFS, XRPD, and TPR). This work consists of four successive parts: the investigation of (i) the palladium precursor liquid solution (in the absence of substrate), (ii) the solid precipitated phase (in the absence of substrate), (iii) the precipitated Pd(2+)-phase on the supports as a function of Pd loading from 0.5 to 5.0 wt % (i.e., the final catalyst for debenzylation reactions), and (iv) the Pd(0)-phase formed upon reduction in H(2) atmosphere at 393 K. A time/pH-dependent UV-vis experiment indicates that Pd(2+) is present in the mother solution mainly as PdCl(2)(H(2)O)(2)] and [PdCl(H(2)O)(3)](+). Upon progressive addition of NaOH (3.0 < pH < approximately 3.8), the concentration of the two complexes is almost constant and then they rapidly disappear because of the precipitation of an amorphous aggregation of Pd(2+)-polynuclearhydroxo complexes. This phase represents a model material for the active supported phase. Thermal treatments at increasing temperature of this phase cause progressive water loss and resulted in a progressive increase in crystallinity typical of a defective PdO-like phase. The EXAFS spectrum of the final catalysts has been found to be intermediate between that of the unsupported amorphous Pd(2+)-polynuclearhydroxo complexes and that of the PdO-like phase. Independent of the support, EXAFS was not able to evidence any fraction of reduced metallic Pd, meaning that all Pd is in the 2+ oxidation state within the sensitivity of the technique (a few percent). Analogously, independent of the support, XRPD was not able to detect the presence of any crystalline supported phase. The Pd local environment of the as-precipitated samples changes slightly as a function of Pd loading from 0.5 to 2.0 wt %: at higher loadings, no further modification has been observed. After reduction in an H(2) atmosphere, two trends have been observed: (i) the dispersion of Pd nanoparticles tends to decrease with increasing Pd concentration, less significantly on Al(2)O(3)-supported samples and more significantly on carbon-supported ones and (ii) the dispersion depends on the carrier following the sequence Al(2)O(3) >> Cp > Cw according to the increasing palladium-support interaction strength.

Synchrotron study of oxygen depletion in a Bi-2212 whisker annealed at 363 K.

Direct evidence is reported of structural and electronic effects induced on a single Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi-2212) whisker during a progressive annealing process. The crystal was investigated by micro X-ray diffraction (micro-XRD), micro X-ray fluorescence and electrical characterization at the European Synchrotron Radiation Facility, during a series of three in situ thermal processes at 363 K. Each step increased the sample resistivity and decreased its critical temperature, up to a semiconducting behaviour. These data correlate with micro-XRD analysis, which shows an increase of the c-axis parameter from 30.56 A to 30.75 A, indicating an oxygen depletion mechanism. Mild temperature annealing could be an effective process to modulate the intrinsic Josephson junctions' characteristics in Bi-2212 whiskers.

Anisotropy in the Raman scattering of a CaFeO2.5 single crystal and its link with oxygen ordering in Brownmillerite frameworks.

Periodic DFT calculations allow an understanding of the strong orientation-dependent Raman spectra of oriented CaFeO2.5 single crystals. Modes involving the oscillation of the apical oxygen (O(ap)) atoms perturb the induced electric dipoles. These are formed by anisotropy in the charge distribution and are found to be strongly enhanced when the electric field of the linearly polarized laser line is parallel to the b axis. For the CaFeO2.5 ordered system, strong polarizability of these modes corresponds to strong Raman intensities. Conversely, the apical oxygen disorder observed in low-temperature oxygen-conducting SrFeO2.5 destroys the long-range coherence of the respective Raman modes, which consequently show a strongly reduced intensity. This study provides a vibrational tool to discriminate between ordered and disordered isomorporphous ABO2.5 Brownmillerite frameworks. Furthermore, in combination with DFT calculations, we have found that the weakening of the interlayer interactions is responsible for the loss of ordering in Brownmillerite compounds.

Silica-supported Ti chloride tetrahydrofuranates, precursors of Ziegler-Natta catalysts.

The structural and electronic properties of silica-supported titanium chloride tetrahydrofuranates samples, obtained by impregnating a polymer-grade dehydroxylated silica with TiCl4(thf)2 and TiCl3(thf)3 complexes, precursors of Ziegler-Natta catalysts, are investigated by means of FT-IR, XAS, XES and diffuse reflectance UV-Vis spectroscopy, coupled with DFT calculations. The properties of the two silica-supported samples are very similar, irrespective of the starting precursor. In both cases, most of the chlorine ligands originally surrounding the Ti sites are substituted by oxygen ligands upon grafting on silica. As a consequence, the electronic properties of silica-supported Ti sites are largely different from those of the corresponding precursors, and in both cases most of the grafted Ti sites have a formal oxidation state of +4. The whole set of experimental data provide evidence that mono-nuclear Ti species are mainly present at the silica surface.