Mechanism of the enhancement of discharge rate property for Nd _0.8Mg_0.2(Ni_0.8Co_0.2)_3.8 hydrogen storage alloy by magnetic annealing

For further improving the rate properties of Nd_0.8Mg _0.2(Ni_0.8Co_0.2)_3.8 hydrogen storage alloy, the alloy was annealed in high magnetic fields (10 T). The results showed that the electrochemical properties and magnetic properties of Nd _0.8Mg_0.2(Ni_0.8Co_0.2)_3.8 hydrogen storage alloy were considerably enhanced. And there was no change of the phase composition. The lattice constants of c and c/a ratio increased for the sample magnetically annealed, yielding uniaxial magnetic anisotropy along the c axis. The increase of c and c/a ratio enlarged interstitial volume, leading to a larger diffusion channel for hydrogen atoms, and resulted in high hydrogen storage capacity and rate properties.