Alloying effects on the hydride formation of Zr(Mn1−xCox)2

To study the alloying effects on ZrMn2–H system, thermodynamic properties of Zr(Mn1−xCox)2 hydride were measured by volumetric method. ZrMn2 gave a single plateau region in the pressure–composition isotherm. On the other hand, double plateaus were clearly observed in Zr(Mn0.7Co0.3)2 and Zr(Mn0.6Co0.4)2–H systems. The appearance of the double plateau characteristics would be explained in view of the hydrogen binding in the tetrahedral occupation sites in Zr(Mn1−xCox)2. Since the hydrogen binding in the tetrahedral 2ZrMnCo site would be less stable than that in the 2Zr2Mn site, the equilibrium pressure increases with increasing cobalt content. The appearance of the first plateau was ascribed the increase in the bonding of Mn–H in 2Zr2Mn site adjoining the 2ZrMnCo site.