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Laves phases / P-T-C isotherms / KineticsIn the MgZn2 hexagonal Laves phases, pseudo-binary compounds are prepared by changing M and Y in the formula: Zr(M,Y! _x)2 M = Fe, Ni, Co, V and Y = Cr, Mn, V. Normally there is a linear decrease in the cell volume with increasing x. Replacement of Fe by Ni in the same proportion produces an anomalous change in the H2 equilibrium pressure by reference to what can be predicted from the volume change. In fact, Ni substituted Laves Phases have the expected properties if the comparative parameter is no longer the cell volume but the tetrahedral H2 host site volume.With this last criteria, both thermodynamic and kinetic parameters can be expressed by linear functions.