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We have studied the complex decomposition mechanism of cubic γ-Mg(BH4)2 (Ia3̅d, a = 15.7858(1) Å) by in-situ synchrotron X-ray diffraction, temperature-programmed desorption, visual observation of the melt, and Fourier transform infrared (FTIR) spectroscopy. The decomposition and release of hydrogen proceeds through eight distinct steps, including two polymorphic transitions before melting, with a new ε-Mg(BH4)2 phase at ca. 150 °C. After melting, strong changes in sample color from yellow to brown to gray are consistent with the unknown Mg–B–H phase(s) (that diffract with high d-spacing halos) in the sample changing from an average composition of MgB2H5.3 at 325 °C, to MgB2.9H3.2 at 350 °C, and to MgB4.0H3.7 by 450 °C. From 350 to 450 °C, the crystalline Mg proportion increases. No combination of previously assigned anionic B n H m species (including MgB12H12 and Mg(B3H8)2) can account for the average composition of the unknown proportion of the sample. This is supported by FTIR spectra showing an absence of terminal B–H resonances in the 2500 cm–1 region that are present for B12H12 and B3H8 anionic species. Our combined analysis strongly indicates the presence of as yet unidentified Mg–B–H phase(s) in postmelted decomposed Mg(BH4)2 samples.

Blue hydrogenated rutile TiO 2 nanoparticles (blue TiO 2 ) are prepared by treating white rutile via an enhanced hydrogenation process (i.e., high pressure and temperature). The materials characterization results demonstrate that the hydrogenation process leads to the increase in the unit cell volume and decrease in the size compared with the untreated white TiO 2 . The electrochemical impedance spectra analyses and theoretical energy calculations using density functional theory (DFT) suggest that the hydrogenation process not only improves electronic conductivity due to the formation of oxygen vacancy in the hydrogenation process but also dramatically augments lithium-ion mass transport within the crystalline lattice due to the introduction of oxygen vacancy and crystalline dislocation. Because of these characteristics resulting from the hydrogenation process, the blue TiO 2 based lithium ion batteries (LIBs) possess significantly higher energy capacity and better rate performance than the white TiO 2 based LIBs. In particular, at the rate of 0.1 and 5 C (1 C = 336 mAh g −1 ), the discharge capacities of the blue rutile are maintained at ca.179.8 and 129.2 mAh g −1 , while the capacities of the white TiO 2 are just ca. 119.6 and 55.5 mAh g −1 , respectively.

This paper describes new sample cells and techniques for in situ powder X-ray diffraction specifically designed for gas absorption studies up to ca 300 bar (1 bar = 100 000 Pa) gas pressure. The cells are for multipurpose use, in particular the study of solid-gas reactions in dosing or flow mode, but can also handle samples involved in solid-liquid-gas studies. The sample can be loaded into a single-crystal sapphire (Al 2 O 3 ) capillary, or a quartz (SiO 2 ) capillary closed at one end. The advantages of a sapphire single-crystal cell with regard to rapid pressure cycling are discussed, and burst pressures are calculated and measured to be $300 bar. An alternative and simpler cell based on a thin-walled silicate or quartz glass capillary, connected to a gas source via a VCR fitting, enables studies up to $100 bar. Advantages of the two cell types are compared and their applications are illustrated by case studies.

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