Observation of Ferromagnetic Clusters in Bi0.125Ca0.875MnO3

The electron doped manganite system, Bi0.125Ca0.875MnO3, exhibits large bulk magnetization of unknown origin. To select amongst possible magnetic ordering models, we have conducted temperature and magnetic field dependent small-angle neutron scattering measurements. Nontrivial spin structure has been revealed. Ferromagnetic spin clusters form in the antiferromagnetic background when temperature is decreased to Tc~108K. With a further reduction in temperature or the application of external magnetic field, the clusters begin to form in larger numbers, which gives an overall enhancement of magnetization below Tc.Comment: 14 pages, 6 figue

Effect of the partial replacement of CaH2 with CaF2 in the Mixed System CaH2 + MgB2

In this work the effect of a partial replacement of CaH2 with CaF2 on the sorption properties of the system CaH2 + MgB2 has been studied. The first five hydrogen absorption and four desorption reactions of the CaH2 + MgB2 and 3CaH2 + CaF2 + 4MgB2 systems were investigated by means of volumetric measurements, high-pressure differential scanning calorimetric technique (HP-DSC), 11B and 19F MAS NMR spectroscopy, and in situ synchrotron radiation powder X-ray diffraction (SR-PXD). It was observed that already during the mixing of the reactants formation of a nonstoichiometric CaF2-xHx solid solution takes place. Formation of the CaF2-xHx solid solution sensibly affects the overall hydrogen sorption reactions of the system CaH2 + MgB2

Effect of Fe additive on the hydrogenation-dehydrogenation properties of 2LiH + MgB2/2LiBH4 + MgH2 system

Lithium reactive hydride composite 2LiBH4 + MgH2 (Li-RHC) has been lately investigated owing to its potential as hydrogen storage medium for mobile applications. However, the main problem associated with this material is its sluggish kinetic behavior. Thus, aiming to improve the kinetic properties, in the present work the effect of the addition of Fe to Li-RHC is investigated. The addition of Fe lowers the starting decomposition temperature of Li-RHC about 30 °C and leads to a considerably faster isothermal dehydrogenation rate during the first hydrogen sorption cycle. Upon hydrogenation, MgH2 and LiBH4 are formed whereas Fe appears not to take part in any reaction. Upon the first dehydrogenation, the formation of nanocrystalline, well distributed FeB reduces the overall hydrogen storage capacity of the system. Throughout cycling, the agglomeration of FeB particles causes a kinetic deterioration. An analysis of the hydrogen kinetic mechanism during cycling shows that the hydrogenation and dehydrogenation behavior is influenced by the activity of FeB as heterogeneous nucleation center for MgB2 and its non-homogenous distribution in the Li-RHC matrix.Fil: Puszkiel, Julián Atilio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Helmholtz-zentrum Geesthacht - Zentrum Für Material- Und Küstenforschung Gmbh;Fil: Gennari, Fabiana Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Centro Atómico Bariloche; ArgentinaFil: Arneodo Larochette, Pierre Paul. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Centro Atómico Bariloche; ArgentinaFil: Ramallo Lopez, Jose Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Vainio, U.. Helmholtz-zentrum Geesthacht - Zentrum Für Material- Und Küstenforschung Gmbh; . Deutsches Elektronen-Synchrotron; AlemaniaFil: Karimi, F.. Helmholtz-zentrum Geesthacht - Zentrum Für Material- Und Küstenforschung Gmbh;Fil: Pranzas, P. K.. Helmholtz-zentrum Geesthacht - Zentrum Für Material- Und Küstenforschung Gmbh;Fil: Troiani, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Centro Atómico Bariloche; ArgentinaFil: Pistidda, C.. Helmholtz-zentrum Geesthacht - Zentrum Für Material- Und Küstenforschung Gmbh;Fil: Jepsen, J.. Helmholtz-zentrum Geesthacht - Zentrum Für Material- Und Küstenforschung Gmbh;Fil: Tolkiehn, M.. Deutsches Elektronen-Synchrotron; AlemaniaFil: Welter, E.. Deutsches Elektronen-Synchrotron; AlemaniaFil: Klassen, T.. Helmholtz-zentrum Geesthacht - Zentrum Für Material- Und Küstenforschung Gmbh;Fil: Bellosta Von Colbe, J.. Helmholtz-zentrum Geesthacht - Zentrum Für Material- Und Küstenforschung Gmbh;Fil: Dornheim, M.. Helmholtz-zentrum Geesthacht - Zentrum Für Material- Und Küstenforschung Gmbh

Effect of the particle size evolution on the hydrogen storage performance of KH doped Mg NH2 2 2LiH

In recent years, many solid state hydride based materials have been considered as hydrogen storage systems for mobile and stationary applications. Due to a gravimetric hydrogen capacity of 5.6 wt and a dehydrogenation enthalpy of 38.9 kJ mol H2, Mg NH2 2 amp; 8201; amp; 8201;2LiH is considered a potential hydrogen storage material for solid state storage systems to be coupled with PEM fuel cell devices. One of the main challenges is the reduction of dehydrogenation temperature since this system requires high dehydrogenation temperatures amp; 8201;200 C . The addition of KH to this system significantly decreases the dehydrogenation onset temperature to 130 C. On the one hand, the addition of KH stabilizes the hydrogen storage capacity. On the other hand, the capacity is reduced by 50 from 4.1 to 2 after the first 25 cycles. In this work, the particle sizes of the overall hydride matrix and the potassium containing species are investigated during hydrogen cycling. Relation between particle size evolution of the additive and hydrogen storage kinetics is described by using an advanced synchrotron based technique Anomalous small angle X ray scattering, which was applied for the first time at the potassium K edge for amide hydride hydrogen storage systems. The outcomes from this investigation show that, the nanometric potassium containing phases might be located at the reaction interfaces, limiting the particle coarsening. Average diameters of potassium containing nanoparticles double after 25 cycles from 10 to 20 nm . Therefore, reaction kinetics at subsequent cycles degrade. The deterioration of the reaction kinetics can be minimized by selecting lower absorption temperatures, which mitigates the particle size growth, resulting in two times faster reaction kinetic

Probleme der Bodenversiegelung in Ballungsraeumen dargestellt am Beipsiel der Freien und Hansestadt Hamburg

SIGLETIB: RO 4383(34) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Observation of ferromagnetic clusters in Bi 0.125 Ca 0.875 MnO 3 Observation of ferromagnetic clusters in Bi 0.125 Ca 0.875 MnO 3

Abstract The electron doped manganite system, Bi 0.125 Ca 0.875 MnO 3 , exhibits large bulk magnetization of unknown origin. To select amongst possible magnetic ordering models, we have conducted temperature and magnetic field dependent small-angle neutron scattering measurements. Non-trivial spin structure has been revealed. Ferromagnetic spin clusters form in the antiferromagnetic background when temperature is decreased to T c ∼ 108 K. With a further reduction in temperature or the application of external magnetic field, the clusters begin to form in larger numbers, which gives an overall enhancement of magnetization below T c