Detailed investigation of ion exchange in ball-milled LiH + MgB2 system using ultra-high field nuclear magnetic resonance spectroscopy

The present study with the detailed 1H–6Li cross polarization NMR analysis confirms the formation of a ternary compound, (Mg1−xLi2x)B2, during ball milling of LiH + (1/2)MgB2 at room temperature. The 6Li sites in (Mg1−xLi2x)B2 exhibit spinning sidebands (SSBs), whereas the 6Li sites in LiH do not. The SSBs and the very short spin-lattice relaxation time manifested by the 6Li sites in (Mg1−xLi2x)B2 indicate that the Li ions in (Mg1−xLi2x)B2 are located between the layered boron structures and close to Mg ions. The formation of (Mg1−xLi2x)B2 explains the previous observation that the LiH + (1/2)MgB2 mixture ball-milled effectively has a greatly enhanced hydriding kinetics at temperatures below the melting point of LiBH4.