Vibronic coupling and band gap trends in CuGeO3 nanorods

We measured the optical response of CuGeO3 nanorods in order to reveal size effects on the electronic properties. The vibronically activated d-to-d color band excitations are activated by the 131 and 478 cm−1 phonons, with the relative contribution of the lower frequency O-Cu-O bending mode increasing with decreasing size until it dominates the process. We also uncover trends in the direct band gap, with the charge transfer edge hardening with decreasing size. These findings advance the understanding of size effects in low-dimensional copper oxides

Magnetoelectric Coupling through the Spin Flop Transition in Ni3TeO6

We combined high field optical spectroscopy and first principles calculations to analyze the electronic structure of Ni3TeO6 across the 53 K and 9 T magnetic transitions, both of which are accompanied by large changes in electric polarization. The color properties are sensitive to magnetic order due to field-induced changes in the crystal field environment, with those around Ni1 and Ni2 most affected. These findings advance the understanding of magnetoelectric coupling in materials in which magnetic 3d centers coexist with nonmagnetic heavy chalcogenide cations.clos

Structure And Dynamics Investigations Of Sr/Ca-Doped Lapo4 Proton Conductors

Proton conductors loom out of the pool of candidate materials with great potential to boost hydrogen alternatives to fossil-based resources for energy. Acceptor-doped lanthanum orthophosphates are considered for solid oxide fuel cells (SOFCs) for their potential stability and conductivity at high temperature. By exploring the crystal and defect structure of x% Sr/Ca-doped LaPO4 with different nominal Sr/Ca concentrations (x = 0-10) with neutron powder diffraction (NPD) and X-ray powder diffraction (XRD), we confirm that Sr/Ca-doped LaPO4 can exist as self-supported structures at high temperatures during solid oxide fuel cell operation. Thermal stability, surface topography, and size distribution are also studied to better understand the proton conductivity for dry and wet compounds obtained at sintering temperatures ranging from 1200 to 1400 °C using a combination of scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and electrochemical impedance spectroscopy (EIS). The results confirm that Sr-doped samples exhibit the highest proton conductivity of our samples and illustrate the impact of material design and versatile characterization schemes on the development of proton conductors with superior functionality

Photovoltaic cells based on ternary P3HT:PCBM: Ruthenium(II) complex bearing 8-(diphenylphosphino)quinoline active layer

ptical, morphological and photovoltaic properties are investigated for ternary solar cells containing a traditional poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric-acid-methyl ester (P3HT:PCBM) bulkheterojunction (BHJ) active layer modified with different concentrations of a novel ruthenium complex [Ru(N-P)$_2$(O-O)], where N-P abbreviates 8-(diphenylphosphino)quinolone and O-O = oxalate dianion. At a low concentration of the Ru-complex (2.5 wt%) the device efficiency is improved by 50% compared with the reference binary devices at ambient conditions. This substantial efficiency enhancement is attributed to the role of the Ru-complex in improving light absorption over a wavelength range of (295–800 nm) in combination with a better matching of the energy levels of the ternary blend system. Moreover, at low concentration, the Ru-complex has a positive impact on the morphology of the active layer in the device. The inclusion of Ru-complex increases the P3HT crystallinity substantially with virtually no effect on the size and orientation of the crystalline lamellae. The enhancement in device efficiency becomes less pronounced with increasing the concentration of the Ru-complex due to the formation of several micron-size domains of [Ru(N-P)$_2$(O-O)] in the ternary active layers. These large domains negatively affect the optical properties and morphology, thus inhibiting efficient charge generation and transport in the corresponding solar cells

Charge and Bonding in CuGeO3 Nanorods

We combine infrared and Raman spectroscopies to investigate finite length scale effects in CuGeO3 nanorods. The infrared-active phonons display remarkably strong size dependence whereas the Raman-active features are, by comparison, nearly rigid. A splitting analysis of the Davydov pairs reveals complex changes in chemical bonding with rod length and temperature. Near the spin-Peierls transition, stronger intralayer bonding in the smallest rods indicates a more rigid lattice which helps to suppress the spin-Peierls transition. Taken together, these findings advance the understanding of size effects and collective phase transitions in low-dimensional oxides

Electronic chirality in the metallic ferromagnet Fe1/3TaS2

We bring together optical spectroscopy and first-principles calculations to reveal the electronic properties of the chiral ferromagnet Fe1/3TaS2. Signatures of chirality are superimposed upon a complex free-carrier response that emanates from both Ta and Fe bands. These include a honeycomb charge density pattern in the Fe layer and a hole → electron pocket crossover at the K point, low-energy excitations between spin split bands that cross the Fermi surface, and clustered rather than well-separated on-site and charge-transfer excitations. These findings advance the understanding of intercalation and symmetry breaking on the fundamental excitations in metallic chalcogenides

Fast Proton Diffusion in Ca-doped LaPO4 studied by Quasi-Elastic Neutron Scattering

We have investigated the diffusion dynamics of protons in hydrated 4.2%Ca-doped LaPO4, a candidate electrolyte for proton-conducting intermediate temperaturefuel cells. The macroscopic and microscopic dynamics have been studied usingelectrochemical impedance spectroscopy (EIS) and quasi-elastic neutron scattering(QENS), respectively. The conductivity of the bulk hydrated sample was determined inthe temperature range of 500−850 °C by EIS and showed a clear signature of protonconductivity with an activation energy of about 1.0 eV. The QENS experiment revealed afast dynamical process below 500 °C that was not observed by EIS. The activation energyof the fast proton diffusion is 0.09 eV in the temperature range from 150 °C to 500 °C