LiSc(BH 4 ) 4 has been prepared by ball milling of LiBH 4 and ScCl 3 . Vibrational spectroscopy indicates the presence of discrete Sc(BH 4 ) 4 -ions. DFT calculations of this isolated complex ion confirm that it is a stable complex, and the calculated vibrational spectra agree well with the experimental ones. The four BH 4 -groups are oriented with a tilted plane of three hydrogen atoms directed to the central Sc ion, resulting in a global 8 + 4 coordination. The crystal structure obtained by high-resolution synchrotron powder diffraction reveals a tetragonal unit cell with a ) 6.076 Å and c ) 12.034 Å (space group P-42c). The local structure of the Sc(BH 4 ) 4 -complex is refined as a distorted form of the theoretical structure. The Li ions are found to be disordered along the z axis.

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We have investigated the crystal structure of Ca(BD4)2 by combined synchrotron radiation X-ray powder diffraction, neutron powder diffraction, and ab initio calculations. Ca(BD4)2 shows a variety of structures depending on the synthesis and temperature of the samples. An unknown tetragonal crystal of Ca(BD4)2, the beta phase has been solved from diffraction data measured at 480 K on a sample synthesized by solid-gas mechanochemical reaction by using MgB2 as starting material. Above 400 K, this sample has the particularity to be almost completely into the beta phase of Ca(BD4)2. Seven tetragonal structure candidates gave similar fit of the experimental data. However, combined experimental and ab initio calculations have shown that the best description of the structure is with the space group P4(2)/m based on appropriate size/geometry of the (BD4)tetrahedra, the lowest calculated formation energy, and real positive vibrational energy, indicating a stable structure. At room temperature, this sample consists mainly of the previously reported alpha phase with space group Fddd. In the diffraction data, we have identified weak peaks of a hitherto unsolved structure of an orthorombic gamma phase of Ca(BD4)2. To properly fit the diffraction data used to solve and refine the structure of the beta phase, a preliminary structural model of the gamma phase was used. A second set of diffraction data on a sample synthesized by wet chemical method, where the gamma phase is present in significant amount, allowed us to index this phase and determine the preliminary model with space group Pbca. Ab initio calculations provide formation energies of the alpha phase and beta phase of the same order of magnitude (delta H < or = 0.15 eV). This indicates the possibility of coexistence of these phases at the same thermodynamical conditions.

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A high-entropy alloy (HEA) of HfNbTiVZr was synthesized using an arc furnace followed by ball milling. The hydrogen absorption mechanism was studied by in situ X-ray diffraction at different temperatures and by in situ and ex situ neutron diffraction experiments. The body centered cubic (BCC) metal phase undergoes a phase transformation to a body centered tetragonal (BCT) hydride phase with hydrogen occupying both tetrahedral and octahedral interstitial sites in the structure. Hydrogen cycling of the alloy at 500 °C is stable. The large lattice strain in the HEA seems favorable for absorption in both octahedral and tetrahedral sites. HEAs therefore have potential as hydrogen storage materials because of favorable absorption in all interstitial sites within the structure.

In-Situ Neutron Diffraction and Performance in Li-Ion Full Cells. ChemRxiv. Preprint. Covers thorough study showing the possible strategies to decouple effect of oxygen deficiency, the presence of Mn 3+ and degree of cation ordering in the high power positive electrode material for lithium ion batteries, LiNi 0.5 Mn 1.5 O 4 . File list (2) download file view on ChemRxiv LNMO_ordering_vs_oxygen_October10.pdf (1.40 MiB) download file view on ChemRxiv Paper3_SI.pdf (277.95 KiB) Cation ordering and oxygen release in LiNi0.5-xMn1.5+xO4-y (LNMO):In-situ neutron diffraction and performance in Li-ion full cells