Origin of Anomalous Lattice Expansion in Oxide Nanoparticles

Abstract

Anomalous lattice expansions have been measured for the first time in monodisperse ${\mathrm{CeO}}_{2-x}$ nanoparticles and in ${\mathrm{BaTiO}}_3$ single nanoparticles by electron diffraction. X-ray photoelectron spectroscopy studies on ${\mathrm{CeO}}_{2-x}$ nanoparticles and ab initio computer simulation on ${\mathrm{BaTiO}}_3$ clusters show that the origin of expansion is the decrease of electrostatic force caused by valence reduction of Ce ions and the increase in ionicity of Ti ions, respectively. The lattice constant change of oxide (ionic) nanoparticles with the increase in ionicity would depend on the structure of the particles. Hence, first-principles calculations of large ionic clusters are indispensable.