A neutron diffraction study of crystal and low-temperature magnetic structures within the (Na,Li)FeGe2O6 pyroxene-type solid solution series

Solid solution compounds along the Li1–x Na x FeGe2O6 clinopyroxene series have been prepared by solid state ceramic sintering and investigated by bulk magnetic and calorimetric methods; the Na-rich samples with x(Na) > 0.7 were also investigated by low-temperature neutron diffraction experiments in a temperature range of 4–20 K. For samples with x(Na) > 0.76 the crystal structure adopts the C2/c symmetry at all measuring temperatures, while the samples display P21/c symmetry for smaller Na contents. Magnetic ordering is observed for all samples below 20 K with a slight decrease of T N with increasing Na content. The magnetic spin structures change distinctly as a function of chemical composition: up to x(Na) = 0.72 the magnetic structure can be described by a commensurate arrangement of magnetic spins with propagation vector k = (½, 0 0), an antiferromagnetic (AFM) coupling within the Fe3+O6 octahedra zig-zag chains and an alternating AFM and ferromagnetic (FM) interaction between the chains, depending on the nature of the tetrahedral GeO4 chains. The magnetic structure can be described in magnetic space group P a21/c. Close to the structural phase transition for sample with x(Na) = 0.75, magnetic ordering is observed below 15 K; however, it becomes incommensurately modulated with k = (0.344, 0, 0.063). At 4 K, the magnetic spin structure best can be described by a cycloidal arrangement within the M1 chains, the spins are within the a–c plane. Around 12 K the cycloidal structure transforms to a spin density wave (SDW) structure. For the C2/c structures, a coexistence of a simple collinear and an incommensurately modulated structure is observed down to lowest temperatures. For 0.78 ≤ x(Na) ≤ 0.82, a collinear magnetic structure with k = (0 1 0), space group P C21/c and an AFM spin structure within the M1 chains and an FM one between the spins is dominating, while the incommensurately modulated structure becomes dominating the collinear one in the samples with x(Na) = 0.88. Here the magnetic propagation vector is k = (0.28, 1, 0.07) and the spin structure corresponds again to a cycloidal structure within the M1 chains. As for the other samples, a transition from the cycloidal to a SDW structure is observed. Based on the neutron diffraction data, the appearance of two peaks in the heat capacity of Na-rich samples can now be interpreted as a transition from a cycloidal magnetic structure to a spin density wave structure of the magnetically ordered phase for the Na-rich part of the solid solution series

Zones of exocytotic release on bovine adrenal medullary cells in culture

Secretion of catecholamines from individual bovine adrenal medullary cells in culture was examined by amperometry with 1-micron radius carbon-fiber electrodes. Vesicular secretion is observed as a series of current spikes upon exposure to a secretagogue. The small size of the electrodes was exploited to map exocytotic release sites on the surface of bovine adrenal medullary cells. These studies reveal for the first time that release sites are spatially localized on endocrine cells in culture for a time scale of at least 15 min. Fluorescent monitoring by confocal microscopy of deposition of dopamine-beta-hydroxylase from the vesicular membrane into the plasma membrane during exocytosis confirms the existence of zones of exocytotic inactivity on the surface of the cell. Measurement of coincident spikes with two adjacent electrodes (2.5-microns radius) has allowed the spatial resolution for measurement of exocytosis to be defined as 2 microns from the projected circumference of the electrode on the surface of the cell. In this small domain, point-source release and diffusional broadening would result in narrow spikes (Schroeder, T. J., Jankowski, J. A., Kawagoe, K. T., Wightman, R. M., Lefrou, C., and Amatore, C. (1992) Anal. Chem. 64, 3077-3083), a feature not seen in the data. Thus, for adrenal medullary cells, release following vesicular fusion is not instantaneous, but is a prolonged event occurring over several milliseconds

Heterogeneity of Graphite Lithiation in State‐of‐the‐Art Cylinder‐Type Li‐Ion Cells

The two‐dimensional lithium distribution in the graphite anode was non‐destructively probed by spatially resolved neutron diffraction for a batch consisting of 34 different cylinder‐type (18650) Li‐ion batteries in fully charged state. The uniformity of the lithium distribution was quantified and correlated to the cell specifications/electrochemistry and to intrinsic cell parameters like electrode thickness, position of current collectors, etc. which were obtained by X‐ray micro‐computed tomography. Non‐uniformities in the lithiation state of the anode from a constant plateau have been observed for the majority of the studied cells. Their location corresponds to the positions of current tabs connecting the electrode stripes and areas of incomplete electrode coating at the beginning and the end of the electrode stripes. Four commonly used schemes of current lid connection were identified. Each of them displays its own effect on the uniformity of the lithiation at the anode and, therefore, variation of the intrinsic state‐of‐charge distribution and, most probably, the ageing behavior of the electrodes

Origin of Ferroelectricity in Orthorhombic LuFeO3_3

We demonstrate that small but finite ferroelectric polarization ($\sim$0.01 $\mu$C/cm$^2$) emerges in orthorhombic LuFeO$_3$ ($Pnma$) at $T_N$ ($\sim$600 K) because of commensurate (k = 0) and collinear magnetic structure. The synchrotron x-ray and neutron diffraction data suggest that the polarization could originate from enhanced bond covalency together with subtle contribution from lattice. The theoretical calculations indicate enhancement of bond covalency as well as the possibility of structural transition to the polar $Pna2_1$ phase below $T_N$. The $Pna2_1$ phase, in fact, is found to be energetically favorable below $T_N$ in orthorhombic LuFeO$_3$ ($albeit$ with very small energy difference) than in isostructural and nonferroelectric LaFeO$_3$ or NdFeO$_3$. Application of electric field induces finite piezostriction in LuFeO$_3$ via electrostriction resulting in clear domain contrast images in piezoresponse force microscopy.Comment: 12 pages, 8 figure

Особенности учета основных средств в бухгалтерском налоговом учете

Основные средства любой компании являются ее главным производственным резервом, результативность которого обеспечивается только в таком случае, если у предприятия правильно построен бухгалтерский и налогового учет представленного имущества. В статье проанализированы различия в учёте основных средств организации в системе бухгалтерского и налогового учёта

Lock-in spin structures and ferrimagnetism in polar Ni2−xCoxScSbO6 oxides

International audienceThe new phase Co2ScSbO6 and Ni2-xCoxScSbO6 solid solutions adopt the polar Ni3TeO6-type structure and order magnetically below 60 K. A series of long-period lock-in [0 0 1/3n] spin structures with n = 5, 6, 8 and 10 is discovered, coexisting with a ferrimagnetic [0 0 0] phase at high Co-contents. The presence of electrical polarisation and spontaneous magnetisations offers possibilities for multiferroic properties

Powder diffraction computed tomography: A combined synchrotron and neutron study

Diffraction and imaging using x-rays and neutrons are widely utilized in different fields of engineering, biology, chemistry and/or materials science. The additional information gained from the diffraction signal by x-ray diffraction and computed tomography (XRD-CT) can give this method a distinct advantage in materials science applications compared to classical tomography. Its active development over the last decade revealed structural details in a non-destructive way with unprecedented sensitivity. In the current contribution an attempt to adopt the well-established XRD-CT technique for neutron diffraction computed tomography (ND-CT) is reported. A specially designed \u27phantom\u27, an object displaying adaptable contrast sufficient for both XRD-CT and ND-CT, was used for method validation. The feasibility of ND-CT is demonstrated, and it is also shown that the ND-CT technique is capable to provide a non-destructive view into the interior of the \u27phantom\u27 delivering structural information consistent with a reference XRD-CT experiment

Измерение параметров солнечных элементов с применением миникомпьютера Beaglebone Black

В сегодняшний день нехватка энергии, загрязнение окружающей среды постепенно увеличивается, в такое ситуаций солнечная энергетика становятся более актуальной для преодоления кризиса ресурсов. Поэтому улучшение методов измерения параметров солнечных элементов является ключевом фактором при исследований и производстве солнечных элементов.С развитием интернета вещей, одним из перспективных направлений развития измерительной техники является создание устройства измерения с помощью миникомпьютера

Energy research with neutrons (ErwiN) and installation of a fast neutron powder diffraction option at the MLZ, Germany

The need for rapid data collection and studies of small sample volumes in the range of cubic millimetres are the main driving forces for the concept of a new high-throughput monochromatic diffraction instrument at the Heinz Maier-Leibnitz Zentrum (MLZ), Germany. A large region of reciprocal space will be accessed by a detector with sufficient dynamic range and microsecond time resolution, while allowing for a variety of complementary sample environments. The medium-resolution neutron powder diffraction option for `energy research with neutrons\u27 (ErwiN) at the high-flux FRM II neutron source at the MLZ is foreseen to meet future demand. ErwiN will address studies of energy-related systems and materials with respect to their structure and uniformity by means of bulk and spatially resolved neutron powder diffraction. A set of experimental options will be implemented, enabling time-resolved studies, rapid parametric measurements as a function of external parameters and studies of small samples using an adapted radial collimator. The proposed powder diffraction option ErwiN will bridge the gap in functionality between the high-resolution powder diffractometer SPODI and the time-of-flight diffractometers POWTEX and SAPHiR at the MLZ