Fig. 2: Temperature dependence of spin disproportionation from simulation and experiment.
From: Temperature-dependent dynamic disproportionation in LiNiO2
a Simulated free energy surface at 300 K, versus Ni magnetic moments and NiO6 octahedral volume, with three basins corresponding to spin states highlighted. b Simulated free energy profiles versus Ni magnetic moments and temperature. Lines are drawn via a Gaussian filter with bandwidth equal to 1 bin of the histogram that defines the free-energy surface. The arrow connecting (a) and (b) highlights the saddle point between the S = ½ and S = 1 states. c Ni L3-edge x-ray absorption spectra of LiNiO2 in inverse partial fluorescence yield (IPFY) mode as a function of temperature. The NaNiO2 spectrum (blue) is offset for clarity. Fits of these spectra to three species are plotted in Supplementary Fig. 1. d Concentrations of Ni species (green: S = 1, purple: S = ½, pink: S = 0) during delithiation from Monte-Carlo sampling of a DFT-based cluster expansion (Methods). The shaded uncertainty values are ±1 s.e. over eight distinct supercell sizes.
