Exceptional Hydrogen Absorption of Palladium Nanoparticles

Abstract

The nanometer-sized metals attract much attention since their physical and chemical properties are substantially different from those of bulk metals. In this work, neutron powder diffraction experiments on the nanoparticles of palladium deuteride, which is the most popular metal hydride, have been performed at 300, 150, and 44 K to investigate the position of the deuterium atoms in the fcc lattice of Pd. The Rietveld analysis revealed that D atoms are located at the tetrahedral (T) sites in addition to the octahedral (O) sites. This is in contrast to the result that only the O sites are occupied in bulk Pd and in other transition metals with the fcc lattice at ambient pressure and temperature. We guess that the T site occupation is due to the change in potential energy caused by the surface and/or distortion effects of nanoparticles.