Effect of Si substitution for Al on the structural and hydrogenation properties of the Zintl phase alloy SrAl₂

In this paper, Al was partially substituted by Si in the Zintl phase alloy SrAl₂ and the structural and hydrogenation properties of the SrAl_2-xSi_x (x = 0.2, 0.4, 0.6, 0.8 and 1.0) alloys were studied by X-ray diffraction (XRD), optical microscopy (OM) and hydrogenation measurements. With the substitution of Al by Si, SrAlSi phase appears in the alloy and the SrAl_2-xSi_x (x = 0.2, 0.4, and 0.6) alloys are all composed of SrAl₂ and SrAlSi phases. The phase abundance of SrAl₂ and SrAlSi is decreased and increased, respectively, when x increases from 0.2 to 0.6. However, the alloy consists of a single SrAlSi phase when x = 0.8 and 1.0. Hydrogenation measurements were made at 573 K under 3 MPa hydrogen pressure. The hydrogen absorption capacity is decreased with increasing the Si substitution for Al, which can be attributed to the smaller hydrogen absorption capacity and slower hydrogenation rate of SrAlSi phase than SrAl₂ phase.