2012 Volume 53 Issue 3 Pages 513-517
Ternary intermetallic compounds, Mg2−xPrxNi4 (0.6 ≤ x ≤ 1.4) were synthesized by induction melting and investigated with respect to hydrogenation properties and structural changes. These compounds have a cubic C15b-type Laves structure (space group F-43m), where Mg and Pr have an ordered arrangement. The lattice parameters increased from a = 0.70101(3) nm to a = 0.71726(8) nm with increase of the Pr content. Mg1.4Pr0.6Ni4 and Mg1.2Pr0.8Ni4 absorbed and desorbed hydrogen up to ∼0.7 H/M reversibly through one plateau in the p-c isotherms. The stoichiometric MgPrNi4 showed two plateaus and its maximum hydrogen content reached to ∼1.0 H/M at 35 MPa. The enthalpy changes of hydrides formation of Mg1.4Pr0.6Ni4 and Mg1.2Pr0.8Ni4 were estimated to be −39.2 and −40.3 kJ/mol H2 respectively. The enthalpy changes of hydrides formation of MgPrNi4 at the lower and higher plateaus were estimated to be −42.4 and −19.6 kJ/mol H2 respectively. The metal sublattice of hydrides Mg1.4Pr0.6Ni4H∼4 and Mg1.2Pr0.8Ni4H∼4 had cubic ordered C15b-type Laves structure same as the crystal structure before hydrogenation while hydride at the lower plateau of the stoichiometric MgPrNi4 had an orthorhombic structure. The hydrogenation of Mg0.8Pr1.2Ni4 and Mg0.6Pr1.4Ni4 led to amorphization.