The Nanoscale Kirkendall Effect in Pd-Based Intermetallic Phases

Abstract

Hollow particles of Pd–X intermetallic phases (X = Ga, Ge, Sn) are prepared by reduction of the respective oxide-supported Pd/XO2 and Pd/X2O3 thin films via the nanoscale Kirkendall effect. Void formation and stability was investigated by (scanning) high-resolution transmission electron microscopy and spectroscopy. Analysis of the selected area electron diffraction patterns after different reductive steps revealed a direct correlation of void size and stability with the composition of the respective intermetallic compounds. Voids only appear for Pd-rich Pd2X phases, whereas for intermetallic compounds of lower Pd content, PdX, the particles are solid again. Energy-filtered electron microscopic images show that the voids are indeed empty and formed by faster Pd outward diffusion compared to X inward diffusion.