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Instruments / Technical Area	Publication Details	Published
I11-High Resolution Powder Diffraction	Potassium octahydridotriborate: diverse polymorphism in a potential hydrogen storage material and potassium ion conductor Jakob B. Grinderslev , Kasper Moller , Yigang Yan , Xi-meng Chen , Yongtao Li , Hai-wen Li , Wei Zhou , Jørgen Skibsted , Xuenian Chen , Torben Jensen Dalton Transactions 46 DOI: 10.1039/C9DT00742C Diamond Proposal Number(s): [17433] Show Abstract ▼ Abstract: Octahydridoborate, i.e. [B3H8]− containing compounds, have recently attracted interest for hydrogen storage. In the present study, the structural, hydrogen storage, and ion conductivity properties of KB3H8 have been systematically investigated. Two distinct polymorphic transitions are identified for KB3H8 from a monoclinic (α) to an orthorhombic (α′) structure at 15 °C via a second-order transition and eventually to a cubic (β) structure at 30 °C by a first-order transition. The β-polymorph of KB3H8 displays a high degree of disorder of the [B3H8]− anion, which facilitates increased cation mobility, reaching a K+ conductivity of ∼10−7 S cm−1 above 100 °C. β-KB3H8 starts to release hydrogen at ∼160 °C, simultaneously with the release of B5H9 and trace amounts of B2H6. KBH4 and K3(BH4)(B12H12) are identified as crystalline decomposition products above 200 °C, and the formation of a KBH4 deficient structure of K3−x(BH4)1−x(B12H12) is observed at elevated temperature. The hydrogen-uptake properties of a KB3H8–2KH composite have been examined under 380 bar H2, resulting in the formation of KBH4 at T ≥ 150 °C along with higher metal hydridoborates, i.e. K2B9H9, K2B10H10, and K2B12H12.	May 2019
I11-High Resolution Powder Diffraction	Trends in synthesis, crystal structure, and thermal and magnetic properties of rare-earth metal borohydrides Jakob B. Grinderslev , Kasper Moller , Martin Bremholm , Torben Jensen Inorganic Chemistry DOI: 10.1021/acs.inorgchem.8b03258 Diamond Proposal Number(s): [15781] Show Abstract ▼ Abstract: Synthesis, crystal structures, and thermal and magnetic properties of the complete series of halide-free rare-earth (RE) metal borohydrides are presented. A new synthesis method provides high yield and high purity products. Fifteen new metal borohydride structures are reported. The trends in crystal structures, thermal behavior, and magnetic properties for the entire series of RE(BH4)x are compared and discussed. The RE(BH4)x possess a very rich crystal chemistry, dependent on the oxidation state and the ionic size of the rare-earth ion. Due to the lanthanide contraction, there is a significant decrease in the volume of the RE3+-ion with increasing atomic number, which correlates linearly with the unit cell volume of the α- and β-RE(BH4)3 polymorphs and the solvated complexes α-RE(BH4)3·S(CH3)2. The thermal analysis reveals a one-step decomposition pathway in the temperature range from 247 to 277 °C for all RE(BH4)3 except Lu(BH4)3, which follows a three-step decomposition pathway. In contrast, the RE(BH4)2 decompose at higher temperatures in the range 306 to 390 °C due to lower charge density on the rare-earth ion. The RE(BH4)3 show increasing stability with increasing Pauling electronegativity, which contradicts other main group and transition metal borohydrides. The majority of the compounds follow Curie–Weiss paramagnetic behavior down to 3 K with weak antiferromagnetic interactions and magnetic moments in accord with those of isolated 4f ions. Some of the RE(BH4)x display varying degrees of temperature-dependent magnetic moments due to low-lying excited stated induced by crystal field effects. Additionally, a weak antiferromagnetic ordering is observed in Gd(BH4)3, indicating superexchange through a borohydride group.	Apr 2019
I11-High Resolution Powder Diffraction	A NaAlH 4 -Ca(BH 4 ) 2 composite system for hydrogen storage Kasper T. Moller , Jakob B. Grinderslev , Torben R. Jensen Journal Of Alloys And Compounds DOI: 10.1016/j.jallcom.2017.05.264 Diamond Proposal Number(s): [12714] Show Abstract ▼ Abstract: Mechanochemical treatment (ball-milling) of NaAlH4-Ca(BH4)2 mixtures leads to partial formation of NaBH4 and Ca(AlH4)2 by a metathesis reaction. The reaction proceeds to different extents depending on the applied ball-milling times, which is confirmed by powder X-ray diffraction and infrared spectroscopy. Additionally, an in-situ synchrotron radiation powder X-ray diffraction study reveals that the metathesis reaction continues due to thermal treatment while the data also supports a two-step decomposition of the formed Ca(AlH4)2. Finally, the reactive hydride composite system was investigated by mass spectrometry and Sieverts' measurement, which reveal release of ∼6 wt% H2 at T < 375 °C.	May 2017

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