Temperature and high-pressure dependent X-ray absorption of SmNiO$_{3}$ at K-Ni and Sm-L$_{3}$ edges

We report XANES and EXAFS measurements of SmNiO$_{3}$ from 20 K to 600 K and up to 38 GPa done at LNLS, Campinas, Brazil, in the DXAS energy dispersive beamline. SmNiO$_{3}$ undergoes an atmospheric pressure insulator to metal transition at T$_{IM}$ $\sim$ 400 K, orders magnetically at T$_{N}$ $\sim$ 205 K, and shares with all RNiO$_{3}$ (R$=$Rare Erath) a negative --dT$_{MI}$/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 Ni$^{3+\delta}+$ Ni$^{3-\delta}$ charge disproportion in a monoclinic distortion turning at T$_{MI}$ into Ni$^{3+}$ in the orthorhombic Pbnm metal oxide phase. Increasing pressure induces Ni-O-Ni angle increments toward more symmetric Ni$^{3+}$ octahedra of rhombohedral R$^-$ 3c space group (metallic LaNiO$_{3})$. 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 e$_{g}$-t$_{2g}$ splitting and a stronger band growing in intensity in the higher symmetry metallic phases associated to e$_{g}$ electron delocalization hopping conductivity. The Ni$^{3+}$ 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 L$_{3}$-edge does not show distinctive behaviors either at 300 K or 20 K up about 35 GPa.