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6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on CaH2 by Materials Project

CaH2 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ca2+ is bonded in a 3-coordinate geometry to eleven H1- atoms. There are a spread of Ca–H bond distances ranging from 2.20–2.67 Å. There are two inequivalent H1- sites. In the first H1- site, H1- is bonded to five equivalent Ca2+ atoms to form distorted HCa5 trigonal bipyramids that share corners with twelve equivalent HCa6 octahedra, corners with eight equivalent HCa5 trigonal bipyramids, edges with six equivalent HCa5 trigonal bipyramids, and faces with six equivalent HCa6 octahedra. The corner-sharing octahedra tilt angles range from 31–59°. In the second H1- site, H1- is bonded to six equivalent Ca2+ atoms to form HCa6 octahedra that share corners with twelve equivalent HCa6 octahedra, corners with twelve equivalent HCa5 trigonal bipyramids, edges with six equivalent HCa6 octahedra, faces with two equivalent HCa6 octahedra, and faces with six equivalent HCa5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 51°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaH2(CO2)2 by Materials Project

CaH2(CO2)2 crystallizes in the tetragonal P4_12_12 space group. The structure is three-dimensional. Ca2+ is bonded to six O2- atoms to form distorted corner-sharing CaO6 octahedra. The corner-sharing octahedral tilt angles are 61°. There are a spread of Ca–O bond distances ranging from 2.33–2.52 Å. C2+ is bonded in a trigonal planar geometry to one H1+ and two O2- atoms. The C–H bond length is 1.11 Å. There is one shorter (1.26 Å) and one longer (1.27 Å) C–O bond length. H1+ is bonded in a single-bond geometry to one C2+ atom. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to one Ca2+ and one C2+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Ca2+ and one C2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaH2(CO2)2 by Materials Project

CaH2(CO2)2 crystallizes in the tetragonal P4_32_12 space group. The structure is three-dimensional. Ca2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ca–O bond distances ranging from 2.33–2.52 Å. C2+ is bonded in a trigonal planar geometry to one H1+ and two O2- atoms. The C–H bond length is 1.11 Å. There is one shorter (1.26 Å) and one longer (1.27 Å) C–O bond length. H1+ is bonded in a single-bond geometry to one C2+ atom. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one Ca2+ and one C2+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Ca2+ and one C2+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Technical and economic aspects of hydrogen storage in metal hydrides

The recovery of hydrogen from such metal hydrides as LiH, MgH2, TiH2, CaH2 and FeTiH compounds is studied, with the aim of evaluating the viability of the technique for the storage of hydrogen fuel. The pressure-temperature dependence of the reactions, enthalpies of formation, the kinetics of the hydrogen absorption and desorption, and the mechanical and chemical stability of the metal hydrides are taken into account in the evaluation. Economic aspects are considered. Development of portable metal hydride hydrogen storage reservoirs is also mentioned.

Schmitt, R.↗
DOE OSTI2021

Evaluation of Thermal Neutron Scattering Cross Sections for CaH 2

Solid metal hydrides have long been considered viable moderators for nuclear reactor designs due to their moderating ratios, hydrogen densities, high dissociation temperatures, and mechanical properties. CaH 2 is an orthorhombic saline-hydride that has recently been investigated and shows promise for use as a moderator in microreactors. At present, there is no Thermal Scatting Law (TSL) evaluation for CaH 2 in the ENDF/B-VIII.0 database. An evaluation does exist in the JEFF-3.3 database, performed by Serot, however it was limited by the implemented methods and thus both drastically over-predicts the incoherent elastic contribution and completely ignores the coherent elastic contribution to scattering from the metal ions. The thermal neutron scattering cross sections of CaH 2 are evaluated in this work to establish accurate data for use in reactor design. The present evaluation corrects the inaccuracies of the JEFF-3.3 data, and yields three distinct libraries: Ca in CaH 2 , H 1 in CaH 2 , and H 2 in CaH 2 .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Electron doping of NdNiO 3 thin films using dual chamber CaH 2 annealing

Hydrogen donor doping has been exploited as a strategy to manipulate the electronic structure and electrical properties of functional oxide systems. Especially, the development of synthetic methods to achieve electron doping of perovskite rare-earth nickelate thin films utilizing interstitial hydrogen is highly desirable considering the rich electronic phase diagram hosting several functional properties. Here, in this work, we present the hydrogenation of NdNiO 3 (NNO) thin films using CaH 2 annealing and the resulting giant modulation of electrical resistivity in hydrogenated NNO (H–NNO) thin films. Magnetron sputtering was employed to deposit epitaxial ~60 nm-thin NNO films on single crystal LaAlO 3 (LAO) substrates. The formation of the pristine perovskite NNO phase was realized after annealing the films at 500 °C for 24 h. CaH 2 annealing of NNO thin films for time durations ranging from 1 to 6 h was performed in a vacuumed ampule with two interconnected chambers at 280 °C. The two-chamber design enables a simple and clean approach for hydrogen doping without physical contact between the powder and sample of interest. X-ray diffraction and Raman spectroscopy revealed the formation of NNO in pristine samples, and the subsequent hydrogen incorporation upon CaH 2 annealing without forming any impurity phases. The conversion of the oxidation state of Ni towards +2 upon CaH 2 annealing was probed using X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. Consequently, a substantial increase in the room-temperature resistivity was observed upon CaH 2 annealing indicating the formation of a strongly correlated electronic configuration of Ni in H–NNO due to electron doping. Overall, the findings of this study highlight the versatility of CaH 2 annealing as an electron doping method to tune the electrical properties of correlated oxides at low temperatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗