Formation, cationic site exchange and surface structure of mechanosynthesized EuCrO3 nanocrystalline particles

Nanocrystalline EuCrO3 particles (similar to 25 nm) have been prepared by pre-milling a 1:1 molar mixture of Eu2O3 and Cr2O3 for 60 h followed by sintering at 700 degrees C (12 h). This temperature is similar to 500-600 degrees C lower than those at which the material, in bulk form, is conventionally prepared. Rietveld analysis of the x-ray powder diffraction pattern of the EuCrO3 nanoparticles favours a structural model involving a slight degree of cationic exchange where similar to 11% of the Eu3+ and Cr3+ ions exchange their normal dodecahedral A-and octahedral B-sites, respectively, in the perovskite-related structure. This cationic site exchange, which is unusual in a perovskite structure, has been well supported by the corresponding room-temperature Eu-151 Mossbauer spectrum of the nanoparticles that in addition to displaying a distribution in the principal component of the EFG tensor (V-zz) at the usual A-sites of the Eu-151 nuclei, also revealed the presence of a subcomponent with similar to 11% area fraction and a considerably increased |V-zz| value that was associated with Eu3+ ions at octahedral B-sites. X-ray photoelectron and Auger electron spectroscopic techniques reveal a complex surface structure where extremely thin layers of un-reacted Eu2O3 and Cr2O3 cover most of the EuCrO3 nanoparticles' surfaces together with some traces of elemental Cr. The binding energies associated with Eu3+ 3d(5/2), Eu3+ 4d(3/2), Cr3+ 2p(3/2) and O2- 1s core-level electrons in EuCrO3 are estimated from the x-ray photoelectron data for the first time.