Structural trends from a consistent set of single-crystal data of REFeAsO (RE = La, Ce, Pr, Nd, Sm, Gd, and Tb)

A new crystal growth technique for single-crystals of REFeAsO (RE = La, Ce, Pr, Nd, Sm, Gd, and Tb) using NaI/KI as flux is presented. Crystals with a size up to 300 $\mu$m were isolated for single-crystal X-ray diffraction measurements. Lattice parameters were determined by LeBail fits of X-ray powder data against LaB6 standard. A consistent set of structural data is obtained and interpreted in a hard-sphere model. Effective radii for the rare-earth metal atoms for REFeAsO are deduced. The relation of the intra- and inter-plane distances of the arsenic atoms is identified as limiter of the phase formation, and its influence on Tc is discussed.Comment: 8 pages, 11 figures, 3 tables, fig. 6 changed to numerical plot, minor changes to the text, accepted for publication in PR

Formation of micro shear bands during cyclic deformation of sub-microcrystalline nickel

Cyclic deformation of sub-microcrystalline nickel at high plastic strain amplitude generated macro shear bands, causing fatal cracking. The macro shear bands consisted of several micro shear bands, each band containing a single layer of elliptical grains that appeared at less than 50° with respect to the loading axis. Micro texture investigations in micro shear bands revealed almost the same texture with similar shear values as in macro shear bands. During cyclic deformation local overlapping of evolving micro shear bands resulted in formation of fatal macro shear bands

Shear banding in sub-microcrystalline nickel at 4 K

International audienceA flat specimen of sub-microcrystalline nickel was tensile tested at 4 K until fracture occurred and subsequently investigated by electron backscatter diffraction in a high resolution scanning electron microscope in order to deduce the local texture in the near crack area. Thus, two sets of intersecting fine slip markings observed on the surface (under +/- 55 degrees with respect to the tensile axis) could be explained as a result of localized simple shear in the bulk material underneath the slip markings. The overall amount of shear in the region near the crack was estimated to be 1.25 based on texture simulations using the viscoplastic self-consistent polycrystal model

Reprint of: Shear banding in sub-microcrystalline nickel at 4 K

A flat specimen of sub-microcrystalline nickel was tensile tested at 4 K until fracture occurred and subsequently investigated by electron backscatter diffraction in a high resolution scanning electron microscope in order to deduce the local texture in the near crack area. Thus, two sets of intersecting fine slip markings observed on the surface (under ±55 with respect to the tensile axis) could be explained as a result of localized simple shear in the bulk material underneath the slip markings. The overall amount of shear in the region near the crack was estimated to be 1.25 based on texture simulations using the viscoplastic self-consistent polycrystal model

Influence of side groups on the performance of infrared absorbing aza-BODIPY organic solar cells

Organic solar cells are a promising technology for a large area conversion of sunlight into electricity. In particular for solar cells based on oligomers (small molecules), efficient donor materials absorbing wavelengths larger than 780 nm are still rare. Here, we investigate three aza-BODIPY dyes absorbing in the infrared. The addition of side groups leads to a red shift of the optical gap from 802 to 818 nm. In optimized devices using these donors in a bulk heterojunction with C-60, we observe a higher charge carrier mobility and a higher power conversion efficiency for the molecules without a methyl or methoxy side group lowering the molecular reorganization energy. Surprisingly, the donor-acceptor blend with the lowest energy loss during the electron transfer to the C-60 yields the highest short circuit current. With increasing size of the attached side chain, the devices exhibit a larger trap density, measured by impedance spectroscopy. Based on the investigation of different blend ratios, we conclude that these traps are mainly present in the donor phase. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei