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23. Structure of Ca[([B[D.sub.4]).sub.2] [beta]-phase from combined neutron and synchrotron x-ray powder diffraction data and density functional calculations

Author

Buchter, F., Lodziana, Z., Remhof, A., Friedrichs, O., Borgschulte, A., Mauron, Ph., Zuttel, A., Sheptyakov, D., Barkhordarian, G., Bormann, R., Chlopek, K., Fichtner, M., Sorby, M., Riktor, M., Hauback, B., and Orimo, S.

Subjects
Calcium compounds -- Structure, Crystals -- Structure, Crystals -- Research, X-rays -- Diffraction, X-rays -- Research, Chemicals, plastics and rubber industries
Abstract

A combination of synchrotron radiation X-ray powder diffraction, neutron powder diffraction and ab initio calculations were used to study the crystal structure of Ca[(B[D.sub.4]).sub.2]. The Ca[(B[D.sub.4]).sub.2] showed variety of coexistence of structures such as [beta]-phase crystal structure, [alpha] phase orthorombic crystal structure and unsolved [gamma] phase.

Published
2008

26. Investigations of Potential Induced Degradation of Silicon Photovoltaic Modules

Author

Schütze, M., Junghänel, M., Friedrichs, O., Wichtendahl, R., Scherff, M., Müller, J., and Wawer, P.

Subjects
PV Modules, Components for PV Systems
Abstract

26th European Photovoltaic Solar Energy Conference and Exhibition; 3097-3102, In the last few years, it became apparent that system voltage can lead to substantial long-term potential induced degradation (PID) of photovoltaic modules via shunting of the incorporated wafer based screen-printed solar cells. The leakage current from the module frames to the cells through the encapsulating material is supposed to cause this effect. Until now the detailed mechanism of shunting is not known although it was speculated that metal ions originating from the soda-lime glass might be responsible. In this study, experimental evidence is presented showing that PID can also be caused by other ions usually not present in photovoltaic modules indicating that the chemical nature of the ions is not relevant for PID. The conditions under which PID occurs in the field are substantiated from the analysis of leakage current data measured outdoor. Starting from these conditions, different options for accelerating a laboratory test for PID are discussed and tested experimentally.

Published
2011
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27. Structure of the orthorhombic γ-phase and phase transitions of Ca(BD₄)₂

Author

Buchter, Florian, Łodziana, Z., Remhof, A., Friedrichs, O., Borgschulte, A., Mauron, Philippe, Züttel, Andreas, Sheptyakov, D., Palatinus, L., Chłopek, K., Fichtner, M., Barkhordarian, G., Bormann, R., and Hauback, B. C.

Abstract

We have solved and refined the crystal structure of the orthorhombic γ-phase of Ca(BD₄)₂ by combined synchrotron X-ray powder diffraction, neutron powder diffraction, and ab initio calculations. Among five structural candidates giving the same quality of the fit of the diffraction data, the structural model with the highest symmetry and space group Pbca is the most appropriate. This is supported by the implicit presence of the Pbca symmetry operations in the low-symmetry space groups in both experimental and DFT calculated structures. The Ca atoms are surrounded by six BD₄ groups that have similar distortions as reported for the β-phase of Ca(BD₄)₂. On the basis of the experimental structures, free energies of the α-, β-, and γ-phases are calculated in the range 300 K < T < 620 K. The phase transitions are observed in the same temperature range by means of X-ray diffraction on Ca(BD₄)₂ + MgD₂ and pure Ca(BD₄)₂ samples. According to the ab initio calculations, the α-phase is the ground state at 0 K. At room temperature, the calculated free energies of the α-phase, β-phase, and γ-phase were found to be within ~0.13 eV/f.u., in agreement with the observed coexistence of these phases. Moreover, calculations provide insight into trends for relative stabilities of α-, β-, and γ-phases. That is, with increasing temperature, the β-phase becomes more stable, while the metastable γ-phase becomes more destabilized with respect to the α-phase.

Published
2010

28. Complex Hydrides

Author

Borgschulte, A., Gremaud, R., Friedrichs, O., Mauron, P., Remhof, A., Züttel, A., Grube, Thomas, and Stolten, Detlef

Published
2010

29. Dynamical properties and temperature induced molecular disordering of LiBH₄ and LiBD₄

Author

Buchter, Florian, Łodziana, Z., Mauron, Philippe, Remhof, A., Friedrichs, O., Borgschulte, A., Züttel, Andreas, Sheptyakov, D., Strässle, Th., and Ramirez-Cuesta, A. J.

Abstract

We report on neutron powder-diffraction experiments, inelastic incoherent neutron-scattering experiments, and density-functional calculations on dynamics, order and disorder properties of LiBH4 and LiBD4. From refinement of LiBD4 structure at 10 and 302 K, we found an almost ideal tetrahedral geometry of BD4 ions (difference between shortest and longest interatomic distances is less than 4% for B-D bond, and less than 3% for D-D bond), close to the calculated geometry. A quantitative agreement was found between experimental and calculated anisotropic temperature factors of individual atoms. For phonon energies

Published
2009

30. Dynamical properties and temperature induced molecular disordering of LiBH4 and LiBD4

Author

Buchter, F., Lodziana, Z., Mauron, Ph, Remhof, A., Friedrichs, O., Borgschulte, A., Zuettel, A., Sheptyakov, D., Straessle, Th, Ramirez-Cuesta, A. J., and Photo Conversion Materials

Subjects
SDG 7 - Affordable and Clean Energy
Abstract

We report on neutron powder-diffraction experiments, inelastic incoherent neutron-scattering experiments, and density-functional calculations on dynamics, order and disorder properties of LiBH4 and LiBD4. From refinement of LiBD4 structure at 10 and 302 K, we found an almost ideal tetrahedral geometry of BD4 ions (difference between shortest and longest interatomic distances is less than 4% for B-D bond, and less than 3% for D-D bond), close to the calculated geometry. A quantitative agreement was found between experimental and calculated anisotropic temperature factors of individual atoms. For phonon energies

Published
2008
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31. Experimental charge density of LiBD4 from maximum entropy method

Author

Buchter, Florian, Łodziana, Z., Remhof, Arndt, Mauron, Philippe, Friedrichs, O., Borgschulte, Andreas, Züttel, Andreas, Filinchuk, Y., Palatinus, L., Buchter, Florian, Łodziana, Z., Remhof, Arndt, Mauron, Philippe, Friedrichs, O., Borgschulte, Andreas, Züttel, Andreas, Filinchuk, Y., and Palatinus, L.

Published
2011

32. A comparative study of the role of additive in the MgH2 vs. the LiBH4-MgH2 hydrogen storage system

Author

Fernández-Camacho, A., Deprez, E., Friedrichs, O., Fernández-Camacho, A., Deprez, E., and Friedrichs, O.

Abstract

The objective of the present work is the comparative study of the behaviour of the Nb- and Ti-based additives in the MgH2 single hydride and the MgH2 + 2LiBH4 reactive hydride composite. The selected additives have been previously demonstrated to significantly improve the sorption reaction kinetics in the corresponding materials. X-Ray Diffraction (XRD), X-Ray Absorption Spectroscopy (XAS), X-Ray Photoelectron Spectroscopy (XPS) and Electron Microscopy (TEM) analysis were carried out for the milled and cycled samples in absence or presence of the additives. It has been shown that although the evolution of the oxidation state for both Nb- and Ti-species are similar in both systems, the Nb additive is performing its activity at the surface while the Ti active species migrate to the bulk. The Nb-based additive is forming pathways that facilitate the diffusion of hydrogen through the diffusion barriers both in desorption and absorption. For the Ti-based additive in the reactive hydride composite, the active species are working in the bulk, enhancing the heterogeneous nucleation of MgB2 phases during desorption and producing a distinct grain refinement that favours both sorption kinetics. The results are discussed in regards to possible kinetic models for both systems. © 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Published
2011

41. Structure of the Orthorhombic γ-Phase and Phase Transitions of Ca(BD4)2

Author

Buchter, F., primary, Łodziana, Z., additional, Remhof, A., additional, Friedrichs, O., additional, Borgschulte, A., additional, Mauron, Ph., additional, Züttel, A., additional, Sheptyakov, D., additional, Palatinus, L., additional, Chłopek, K., additional, Fichtner, M., additional, Barkhordarian, G., additional, Bormann, R., additional, and Hauback, B. C., additional

Published
2009
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46. Structure of Ca(BD4)2 β-Phase from Combined Neutron and Synchrotron X-ray Powder Diffraction Data and Density Functional Calculations

Author

Buchter, F., primary, Łodziana, Z., additional, Remhof, A., additional, Friedrichs, O., additional, Borgschulte, A., additional, Mauron, Ph., additional, Züttel, A., additional, Sheptyakov, D., additional, Barkhordarian, G., additional, Bormann, R., additional, Chłopek, K., additional, Fichtner, M., additional, Sørby, M., additional, Riktor, M., additional, Hauback, B., additional, and Orimo, S., additional

Published
2008
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