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|Type:||Artigo de periódico|
|Title:||Structural Changes In Rnio3 Perovskites (r = Rare Earth) Across The Metal-insulator Transition|
|Abstract:||Rare earth nickel oxide perovskites (RNiO3, R = rare earth) have, except for LaNiO3, a metal-insulator (MI) phase transition as temperature decreases. The transition temperature (TMI) increases as the R-ion becomes smaller. They also present, at low temperatures, a complex antiferromagnetic order. For lighter R-ions (e.g. Pr and Nd), the antiferromagnetic transition temperature (TN) is close to TMI, while for heavier R-ions (e.g. Eu, Sm), TMI and TN are very far apart, suggesting that the magnetic and electronic behaviors are not directly coupled. Even though Ni3+ is a Jahn-Teller ion, no distortion in the NiO6 octahedra was found for RNiO3 perovskites with R = Pr, Nd, Sm and Eu. In this work we have measured EXAFS at Ni K edge for samples of PrNiO3, NdNiO3 and EuNiO3. The Fourier transform spectra for the three samples show a clear splitting in the first peak at the insulating phase. This splitting corresponds to two or more different Ni-O distances. This indicates that there is either a distortion in the NiO6 octahedra or there are two different Ni sites at the insulating phase. © 2002 Elsevier Science B.V. All rights reserved.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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