Hydrogen storage in Mg: A most promising material

Materials for hydrogen-based energy storage – past, recent progress and future outlook

Magnesium based materials for hydrogen based energy storage: Past, present and future

Mechanochemical synthesis of hydrogen storage materials

Magnesium hydride has been studied extensively for applications as a hydrogen storage material owing to the favourable cost and high gravimetric and volumetric hydrogen densities. However, its high enthalpy of decomposition necessitates high working temperatures for hydrogen desorption while the slow rates for some processes such as hydrogen diffusion through the bulk create challenges for large-scale implementation. The present paper reviews fundamentals of the Mg–H system and looks at the recent advances in the optimisation of magnesium hydride as a hydrogen storage material through the use of catalytic additives, incorporation of defects and an understanding of the rate-limiting processes during absorption and desorption.

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Review of magnesium hydride-based materials: development and optimisation

Structure of the high pressure phase γ-MgH2 by neutron powder diffraction

The changes of the chemical structure of and of the superconducting transition temperature associated with Ca doping have been investigated by means of neutron and x-ray powder diffraction, oxygen content determination and magnetic susceptibility measurements. In this work, we were able to show that the depression of superconductivity in Ca-substituted orthorhombic is related to essential structural changes. Using the cation - oxygen distances obtained by neutron diffraction at 1.5 K we calculated the bond valence sums of the cations. This allows us to estimate the charge distribution within the structure and yields a direct correlation between structural changes induced by Ca doping and . Our results show clearly that Ca doping leads to an overdoping of which cannot be reached by oxygen non-stoichiometry alone.

http://iopscience.iop.org/article/10.1088/0953-8984/8/45/021/pdf

The influence of Ca doping on the crystal structure and superconductivity of orthorhombic

The temperature dependence of the relaxation rate of crystal-field excitations in the slightly underdoped HoBa2Cu4O8 and Er2Ba4Cu7O14.92 high-temperature superconductors has been investigated by means of neutron scattering measurements. Our data show clear evidence for the opening of an electronic gap in the normal state at T* ≈ 200 K far above Tc. The temperature evolution of the relaxation rate appears to be extremely dependent upon the energy at which the susceptibility is being probed. This points to a strongly anisotropic gap function which is tentatively modelled to be of the form s + id3, with Δs/Δd ≈ 0.2.

Pseudogap and order-parameter symmetry in the underdoped high-Tc compounds HoBa2Cu4O8 and Er2Ba4Cu7O14.92: A neutron crystal-field study

In this work, the structural effects of the Ca substitution in YBa 2 Cu 3 O 7−σ (Ca-123) have been studied by X-ray single crystal structure analysis for the first time. The structure refinements of three single crystals show that at low Ca concentrations ( 3+ ions are substituted, while at higher concentrations Ca 2+ also replaces Ba 2+ . Remarkably, no difference in the structural changes has been observed that are due to the apparent substitution for Ba 2+ with Ca 2+ in the more heavily doped samples. Changes in atomic parameters and bond lengths are observed upon Ca doping which are similar in Ca-124 and Ca-247 single crystals. In contrast to ceramic samples, our Ca-123 single crystals are not superconducting probably due to Al doping from the crucible. However, considering doped superconductors, the discussion of structural changes with doping is quite interesting as this work is the first structure refinement of Ca-123 single crystals.

G. Böttger

Papers

Structure of the high pressure phase γ-MgH2 by neutron powder diffraction

The influence of Ca doping on the crystal structure and superconductivity of orthorhombic

Pseudogap and order-parameter symmetry in the underdoped high-Tc compounds HoBa2Cu4O8 and Er2Ba4Cu7O14.92: A neutron crystal-field study

Ca doping of YBa2Cu3O7−σ single crystals: structural aspects

Neutron diffraction study of the location of deuterium in the deuterium-stabilized HfTi2D4 phase