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

Widatallah, H. M.; Al-Harthi, S. H.; Johnson, C.; Klencsár, Z.; Gimelseed, A. M.; Moore, E. A.; Al-Rawas, A. D.; Wynter, C. I. and Brown, D. E. (2011). Formation, cationic site exchange and surface structure of mechanosynthesized EuCrO3 nanocrystalline particles. Journal of Physics D: Applied Physics, 44(26), article no. 265403.

DOI: https://doi.org/10.1088/0022-3727/44/26/265403

Abstract

Nanocrystalline EuCrO3 particles (~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°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 (Vzz) at the usual A-sites of the 151Eu nuclei, also revealed the presence of a subcomponent with ~11% area fraction and a considerably increased |Vzz| 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+ 3d5/2, Eu3+ 4d3/2, Cr3+ 2p3/2 and O2− 1s core-level electrons in EuCrO3 are estimated from the x-ray photoelectron data for the first time.

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