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

Nanocrystalline EuCrO₃ particles (∼25 nm) have been prepared by pre-milling a 1 : 1 molar mixture of Eu₂O₃ and Cr ₂O₃ for 60 h followed by sintering at 700 °C (12 h). This temperature is ∼500-600 °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 ∼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 ¹⁵¹Eu Mössbauer 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 ¹⁵¹Eu nuclei, also revealed the presence of a subcomponent with ∼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 Eu ₂O₃ 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 O ^2- 1s core-level electrons in EuCrO₃ are estimated from the x-ray photoelectron data for the first time.