Atomic structure analysis of Pd nano-cluster in nano-composite Pd/ZrO2 absorbing Deuterium

Structural analysis of high density Deuterium absorbed Pd particles of 5 nm size dispersed in ZrO2 has been carried out using XAFS (X-ray Absorption Fine Structure) techniques. X-ray absorption spectra around the Pd K-absorption edge were observed and analyzed. The Pd-Pd bonding distance in the free Pd lattice of the 5nm cluster was enlarged by 0.08 - 0.09 A during absorption of deuterium, and it completely reverted to its original state with the release of deuterium while maintaining the crystal lattice symmetry. These changes provides evidence that deuterium locates not on the surface of the Pd particle, but rather within the Pd crystal lattice. XANES (X-ray Absorption Near Edge Structure) spectra clearly indicated that the valency of Pd atom did not change on absorbing Deuterium atoms, resulting in no reaction of the absorbed Deuterium atoms with Pd atoms. The hydrogen dispersion mechanism was also discussed quantum-mechanically through electron-lattice interaction, and the possible models of deuterium position in the Pd lattice were also discussed. The 5nm-cluster of Pd was not supported by any oxygen or zirconium ion in ZrO2, but the cluster floated in hole by the repulsion of each electron of Pd and ZnO2. Finally, a new approach to seek after the Deuterium position from X-ray absorption spectra is proposed. (author)