Ionic Mobility in Metallic Sodium Nanoparticles Confined to Porous Glass

Metallic sodium nanoparticles can be used in numerous applications. This requires thorough investigation of their properties. To study the impact of size reduction on the ionic mobility in solid sodium, we carried out ²³Na NMR measurements of the Knight shift and spin–lattice relaxation for sodium nanoparticles embedded into a porous glass with a mean pore size of 23 nm and in bulk sodium. Pronounced acceleration of relaxation in nanoparticles compared to bulk was revealed within a temperature range from 190 to 293 K, while the Knight shift nearly coincided with that in bulk solid sodium. In addition, the rate of magnetization recovery after inversion depended on magnetic field and the recovery curves were non-single exponential. The results were treated assuming the emergence of a noticeable quadrupole contribution to relaxation due to coupling of nuclear quadrupole moments with electric field gradients caused by ionic mobility intensified under nanoconfinement. The correlation time of ionic mobility was found for sodium nanoparticles at different temperatures. The activation energy was evaluated and was shown to be much smaller than in bulk solid sodium.