Nanopowder diffraction analysis beyond the Bragg law applied to palladium

Abstract

A method of powder diffraction analysis is proposed that is applicable to transition metal nanoparticles and which has been applied to palladium. From results of simulations it is shown that: (a) the overall average lattice constant of small transition metal clusters decreases with decreasing size of the cluster as a result of surface contraction; (b) the shift of a diffraction peak position driven by chemisorption increases monotonically with the decrease of cluster size and can be used for the estimation of cluster size; (c) the peak broadening of small clusters may be larger than that resulting from their size; the additional contribution originates from a high density of defects; (d) the extent of the microstrain may be evaluated from the peak broadening and the rate of attenuation of peak intensity; (e) the intensity scattered by small palladium clusters indicates significant surface disorder that may vary during a change of gas atmosphere and during chemisorption of oxygen at the surface.