Calcium hydride and deuteride studied by neutron diffraction and NMR

Structure and vibrational spectra of calcium hydride and deuteride

“…The refined structures at 9 and 298 K indicate that the lattice parameters, bond lengths, and displacement parameters systematically increase with elevated temperature with no significant structural changes. Differences in the present lattice parameters compared to prior results [2,3] may be due to poorer diffractometer resolutions, insufficient 2θ ranges, small errors in neutron wavelengths, or possible different impurity levels and/or CaD 2−x stoichiometries in the earlier studies. Consistent with previous studies [2,3], the crystal structure of CaD 2 provides two different four-fold positions for D atoms: the D1 position is situated within Ca tetrahedra as well as surrounded by eight other D atoms; the D2 position is situated within severely distorted Ca octahedra so as to be coordinated with only five Ca neighbors (see Fig.…”

“…62). The initial atomic positions corresponded to those reported by Andresen et al [3]. The experimental, fitted, and difference profiles of the neutron diffraction patterns for the final refined structure are shown in Fig.…”

“…From a later neutron powder diffraction (NPD) investigation (1962) [2], different hydrogen positions were essentially determined, but the crystallographic study was carried out on data with relatively poor resolution and intensity, and the resultant structure had to rely partly on geometrical considerations. The accuracy of the hydrogen atomic positions was improved by a later NPD study (1977) performed on CaD 2 [3]. Although an early low-resolution neutron vibrational spectroscopy (NVS) study of alkaline-earth hydrides reported a vibrational density of states spectrum for CaH 2 , the vibrational bands were poorly resolved and failed to reveal a complete and detailed picture of all phonon modes [4].…”

Structure and hydrogenation properties of the ternary alloys Ca2−xMgxSi (0≤x≤1)

“…MgH 2 possesses P4 2 /mnm symmetry [7], whereas CaH 2 possesses Pnma symmetry [8][9]. Mg 2 Si forms a cubic antifluorite structure [10], whereas Ca 2 Si crystallizes in an orthorhombic antiPbCl 2 or Co 2 Si-type structure [11].…”

Ab initio prediction of high-pressure structural phase transition in BaH2

“…CaH 2 , SrH 2 , BaH 2 , EuH 2 , and YbH 2 have the same space group and lattice parameter ratios (c/a; (a + c)/b) at ambient conditions [1][2][3]. They crystallize in the orthorhombic phase (Co 2 Si-type) having space group D 16 2h (Pnma) [4].…”