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

NESTOR E. MASSA; ALINE Y. RAMOS; HELIO C. N. TOLENTINO; NARCIZO M. SOUZA-NETO; JAIRO FONSECA, JR.; JOSE´ ANTONIO ALONSO

San Antonio, Texas

Congreso; American Physical Society March Meeting; 2015

American Physical Society

We report XANES and EXAFS measurements of SmNiO3 from 20 K to 600 K and up to 38 GPa done at LNLS, Campinas, Brazil, in the DXAS energy dispersive beamline. SmNiO3 undergoes an atmospheric pressure insulator to metal transition at TIM ∼ 400 K, orders magnetically at TN ∼ 205 K, and shares with all RNiO3 (R=Rare Earth) a negative --dTMI/dP slope. Ni white line peak energies show an abrupt 2.4 GPa and 8.11 GPa valence discontinuity at 300 K and at 20 K respectively, due to non-equivalent Ni sites with Ni3+δ+ Ni3−δ charge disproportion in a monoclinic distortion turning at TMI into Ni3+ in the orthorhombic Pbnm metal oxide phase. Increasing pressure induces Ni-O-Ni angle increments toward more symmetric Ni3+ octahedra of rhombohedral R− 3c space group (metallic LaNiO3). At 38 GPa, there is a clear split of the main EXAFS band according to cell volume decrease due to contraction. Pre-edge tail accounts for eg-t2g splitting and a stronger band growing in intensity in the higher symmetry metallic phases associated to eg electron delocalization hopping conductivity. The Ni3+ post-edge becomes smoother and intensity increased by the reduction of electron-phonon interaction as the pressure-induced phases set in. We also found that Sm L3-edge does not show distinctive behaviors either at 300 K or 20 K up about 35 GPa.