Temperature and high-pressure dependent x-ray absorption of SmNiO3 at the Ni K and Sm L3 edges - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Materials Research Express Année : 2015

Temperature and high-pressure dependent x-ray absorption of SmNiO3 at the Ni K and Sm L3 edges

Résumé

Wereport on x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) measurements of SmNiO3 from 20 Kto 600 Kand up to 38 GPa at the NiKand Sm L3 edges. A multiple component pre-NiKedge tail is understood, originating from 1 s transitions to 3d-4p states while a post-edge shoulder increases distinctively smoothly, at about the insulator to metal phase transition (TIM), due to the reduction of electron–phonon interactions as the Ni 3d andO 2p band overlap triggers the metallic phase. This effect is concomitant with pressure-induced Ni-O-Ni angle increments toward more symmetric Ni3+ octahedra of the rhombohedral R¯3c space group. Room temperature pressure-dependent Ni white line peak energies have an abrupt∼3.10±0.04 GPa valence discontinuity from non-equivalent Ni3+δ+Ni3–δ charge disproportionate net unresolved absorber turning at∼TIM into Ni3+ of the orthorhombic Pbnm metal oxide phase. At 20 Kthe overall white line response, still distinctive at TIM∼8.1±0.6 GPa is much smoother due to localization. Octahedral bond contraction up to 38 GPa and at 300 Kand 20 Kshow breaks in its monotonic increase at the different structural changes. The SmL3 edge does not show distinctive behaviors either at 300 Kor 20 Kup to about 35 GPa but the perovskite Smcage, coordinated to eight oxygen atoms, undergoes strong uneven bond contractions at intermediate pressures where we found the coexistence of octahedral and rhombohedral superexchange angle distortions.Wefound that the white line pressure-dependent anomaly may be used as an accurate alternative for delineating pressure– temperature phase diagrams.

Dates et versions

hal-01362945 , version 1 (09-09-2016)

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Citer

Nestor E. Massa, Aline Y. Ramos, Helio C.N. Tolentino, Jairo Fonseca, Narcizo M. Souza-Neto, et al.. Temperature and high-pressure dependent x-ray absorption of SmNiO3 at the Ni K and Sm L3 edges. Materials Research Express, 2015, 2 (12), pp.126301. ⟨10.1088/2053-1591/2/12/126301⟩. ⟨hal-01362945⟩

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