Structure and hydrogenation properties of the ternary alloys Ca 2− xMg xSi (0 ≤ x ≤ 1)

Abstract

Partially Mg-substituted Ca 2Si alloys (Ca 2− x Mg x Si, 0 ≤ x ≤ 1) were synthesized via high-temperature evacuation of CaH 2/MgH 2/Si ball-milled mixtures. Neutron diffraction refinements showed that Ca 2− x Mg x Si (0 < x < 1) samples are not single-phase solid-solutions, but rather (1− x)Ca 2Si + xCaMgSi mixed phases. Hydrogen absorption measurements indicated that, although pure Ca 2Si ( 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 H 2 and 473–573 K. Thus, hydrogen absorption behaviors of the intermediate compositions (0 < x < 1) are dominated by the Ca 2Si component, as evidenced by the isotherm measurements and neutron vibrational spectra.