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

Partially Mg-substituted Ca2Si alloys (Ca2−xMgxSi, 0 ≤ x ≤ 1) were synthesized via high-temperature evacuation of CaH2/MgH2/Si ball-milled mixtures. Neutron diffraction refinements showed that Ca2−xMgxSi (0 < x < 1) samples are not single-phase solid-solutions, but rather (1−x)Ca2Si + xCaMgSi mixed phases. Hydrogen absorption measurements indicated that, although pure Ca2Si (x = 0) is readily hydridable and forms an unusual amorphous-hydride phase, pure CaMgSi (x = 1) does not noticeably absorb hydrogen up to 7 MPa H2 and 473–573 K. Thus, hydrogen absorption behaviors of the intermediate compositions (0 < x < 1) are dominated by the Ca2Si component, as evidenced by the isotherm measurements and neutron vibrational spectra.