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The crystal structure and electronic properties of Ca2.5Sr0.5GaMn2O8 has been studied by neutron diffraction and muSR spectroscopy. The results show that short-range 2D magnetic order begins to develop within the perovskite-bilayers of MnO6 octahedra.

The efficient management of heat is a key issue when considering the performance of electrical devices. To reduce the probability of their failure an effective heat dissipation should be ensured. The thermal conductivity of pure epoxy is low and can be improved through the addition of fillers. Graphene has been considered as an adequate filler, due to its excellent thermal conductivity. However, graphene‐based composites also show a high electrical conductivity, which limits their application as an electrical insulation considerably. The presented work shows that it is possible to enhance thermal conductivity through the incorporation of a new class of hybrid filler, namely a masterbatch of graphene nanoplatelets (GNPs) and a standard filler like silica. This unique structural design combines the advantages of both, GNPs and silica powder, resulting in composites that not only show high thermal conductivity, but also preserve electrical insulation functionality. A modified processing method leads to the improvement of thermal conductivity. GNPs‐silica hybrid epoxy composites with only 2 wt% of GNPs reached 1.54 W/mK, whereas the volume resistivity remained at the level of 1015 Ω cm. The unique scientific aspect, namely temperature dependence of thermal conductivity, was studied. The presented novel hybrid composites show great potential in applications requiring electrical insulation with enhanced thermal conductivity in high voltage devices. POLYM. COMPOS., 39:E1682–E1691, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The results of thermal conductivity study of epoxy-matrix composites filled with different type of powders are reported. Boron nitride and aluminum nitride micro-powders with different size distribution and surface modification were used. A representative set of samples has been prepared with different contents of the fillers. The microstructure was investigated by SEM observations. Thermal conductivity measurements have been performed at room temperature and for selected samples it was also measured as a function of temperature from 300 K down to liquid helium temperatures. The most spectacular enhancement of the thermal conductivity was obtained for composites filled with hybrid fillers of boron nitride-silica and aluminum nitride-silica. In the case of sample with 31 vol.% of boron nitride-silica hybrid filler it amounts to 114% and for the sample with 45 vol.% of hybrid filler by 65% as compared with the reference composite with silica filler. However, in the case of small aluminum nitride grains application, large interfacial areas were introduced, promoting creation of thermal resistance barriers and causing phonon scattering more effective. As a result, no thermal conductivity improvement was obtained. Different characters of temperature dependencies are observed for hybrid filler composites which allowed identifying the component filler of the dominant contribution to the thermal conductivity in each case. The data show a good agreement with predictions of Agari-Uno model, indicating the importance of conductive paths forming effect already at low filler contents. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The present work deals with nitrogen-doped stoichiometric TiO2:N and non-stoichiometric TiO2−x:N thin films deposited by means of dc-pulsed reactive sputtering for application as photoanodes for hydrogen generation from water, using solar energy. Stoichiometric thin films of TiO2 crystallize as a mixture of anatase and rutile while rutile phase predominates in TiO2:N at higher nitrogen flow rates as shown by X-ray diffraction at grazing incidence, XRD GID. Lack of bulk nitridation of stoichiometric TiO2:N is indicated by valence-to-core X-ray emission spectroscopy, XES, analysis. The energy band gap as well as flat band potential remain almost unaffected by increasing nitrogen flow rate in this case. In contrast to that, non-stoichiometric thin films of TiO2-x:N demonstrate systematic evolution of the structural, morphological, optical and photolectrochemical properties upon increasing level of nitrogen doping. Pronounced changes in the growth pattern of non-stoichiometric TiO2-x:N upon varied nitrogen flow rate, demonstrated by scanning electron microscopy, SEM, can be easily correlated with the crystallographic properties studied by XRD GID. Relative positions of Kβ'' XES lines of the TiO2-x:N thin films, which depend strongly on the nature of the ligands and their local coordination, change with the increasing nitrogen flow. Doping of nonstoichiometric titanium dioxide with nitrogen shifts the absorption spectrum towards the visible range and increases considerably the flat band potential which is beneficial for water photolysis. [ABSTRACT FROM AUTHOR]

Abstract: A systematic study of LaMn1− x Co x O3 perovskite series by means of X-ray absorption spectroscopy in the extended X-ray absorption fine structure (EXAFS) range of the K-absorption edge of Mn is reported. The Mn–K edge absorption measurements in the EXAFS region were performed to study the local surrounding of Mn ions. Polycrystalline powder samples of LaMn1− x Co x O3 (x=0, 0.02; 0.2; 0.4; 0.5; 0.6; 0.8) prepared by solid-state reaction were used. The EXAFS spectra were analyzed with the FEFF8 computer program. The Mn–O distances of Mn to the nearest oxygen surroundings were evaluated for the samples in the series and compared with the Co–O distances obtained by EXAFS in V. Procházka et al., JMMM 310 (2007) 197 and with results of X-ray powder diffraction in C. Autret, J. Phys. Condens. Matter 17 (2005) 1601. [Copyright &y& Elsevier]

The temperature dependence of the crystal structure and electronic properties of brown millerite- like Ca2.5Sr0.5GaMn2O8 has been studied by neutron powder diffraction and μSR spectroscopy. The results show that short-range 2D magnetic order begins to develop within the perovskite-like bilayers of MnO6 octahedra approximately 50 K above the 3D Neel temperature of ∼150 K. The bilayers show a structural response to the onset of magnetism throughout this temperature range whereas the GaO4 layers that separate the bilayers only respond below the 3D ordering temperature. XANES spectroscopy shows that the sample contains Mn3+ and Mn4+ cations in a 1:1 ratio, and the behavior in the region of the Neel transition is interpreted as a local charge ordering. Electron diffraction and high-resolution electron microscopy have been used to show that the local microstructure is more complex than the average structure revealed by neutron diffraction, and that microdomains exist in which the GaO4 tetrahedra show different orientations. It is argued that the bonding requirements of diamagnetic gallium control the electronic behavior within the perovskite-like bilayers. [ABSTRACT FROM AUTHOR]

Focused electron beam-induced deposition using the heteroleptic complex (η 3 -C 3 H 5 )Ru(CO) 3 Br as a precursor resulted in deposition of material with Ru content of 23 at. %. Transmission electron microscopy images indicated a nanogranular structure of pure Ru nanocrystals, embedded into a matrix containing carbon, oxygen, and bromine. The deposits were purified by annealing in a reactive 98% N 2 /2% H 2 atmosphere at 300 °C, resulting in a reduction of contaminants and an increase of the Ru content to 83 at. %. Although a significant volume loss of 79% was found, the shrinkage was observed mostly for vertical thickness (around 75%). The lateral dimensions decreased much less significantly (around 9%). Deposition results, in conjunction with previous gas-phase and condensed-phase surface studies on the electron-induced reactions of (η 3 -C 3 H 5 )Ru(CO) 3 Br, provide insights into the behavior of allyl, carbonyl, and bromide ligands under identical electron beam irradiation.