Charge disproportionation inRNiO3perovskites (R=rareearth) from high-resolution x-ray absorption spectroscopy

Abstract

High-resolution x-ray absorption measurements reveal a rare-earth-dependent splitting of the Ni K edge in the insulating, charge-disproportionated state of the whole RNiO 3 perovskite family. The splitting is five times larger for LuNiO 3 ͓2.5͑1͒ eV͔ than for PrNiO 3 ͓0.5͑3͒ eV͔, suggesting that the charge transfer between Ni 3+␦ and Ni 3−␦ decreases by approaching the itinerant limit and is larger for the heavier lanthanides than suggested in previous studies. The spectroscopic signature of the two Ni sites remains visible above the metal-insulator transition, in agreement with the persistence of dynamic Ni 3+␦ / Ni 3−␦ charge fluctuations in the metallic phase. This last result generalizes the occurrence of charge disproportionation as alternative to Jahn-Teller distortions to the dynamic regime, giving further support to recent theoretical work ͓I.

Spin-moment formation and reduced orbital polarization in LaNiO3/LaAlO3superlattice:LDA+UHan1, Veenendaal2 2012Phys. Rev. B224182View full textAdd to dashboardCite

“…Moreover Fig. 1(a) and (b) indicate the possibility of AFM ground state in the negative U region which is more or less related to the reported charge disorders in the nickelate systems 32,33 . Therefore one needs to be careful in the interpretation of our LDA+U results on the FM spin ground state as an indication of long range ordered ground state as one may see in the actinide systems for example 34,35 .…”

“…However it should be noted that the muon spin rotation (µSR) experiment by Boris et al 10 is not well interpreted in the long range FM ordering picture even though the µSR is basically a local probe and that the origin of metalinsulator phase transition in the nickelate series are not clearly understood yet. Especially regarding the charge disproportionation or ordering in nickelates, the conventional LDA+U has a clear limitation to describe such phenomena 32,33 . Moreover Fig.…”

Sign reversal of magnetoresistance in a perovskite nickelate by electron doping

“…Carrier doping by electrostatic gating or chemical substitution is an active field to modify electronic properties of nickelates [11][12][13][14][15] at the same time serving as a tool to understand and possibly control the metal insulator transition (MIT) phenomenon in nickelates. Earlier studies regarded nickelates as charge transfer insulators 16 whereas in recent works, the origin of insulating phase in nickelates has been attributed to charge disproportionation of the Ni site with an accompanying structural change from orthorhombic to monoclinic phase [17][18][19][20] . Electrolytic gating measurements on thin films of NdNiO3 point towards a Mott-type mechanism where the MIT is driven by critical carrier density that is controlled by the gate voltage 11 .…”

Total energy calculations using DFT+DMFT: Computing the pressure phase diagram of the rare earth nickelates

“…The rare earth nickelates provide a crucial challenge to theoretical methodologies because they exhibit a metal-insulator transition which is closely tied to a large-amplitude two-sublattice bond-length disproportionation in which the mean Ni-O bond length becomes larger for Ni sites on one sublattice and smaller on the other [16]. The electronic state has been the subject of substantial discussion [17][18][19][20][21][22] but has now been identified as a site-selective Mott transition [23]. The location of the phase boundaries in the pressure-temperature plane varies across the rare earth series [16,18,[24][25][26][27], with Lu having the highest critical temperature and pressure and La remaining metallic down to lowest temperature at ambient pressure.…”