Fig. 2: Resonant inelastic X-ray scattering (RIXS) chemical shifts and their correlation to transition metal (TM) ionic radii.

a RIXS 3D1 energy and TM ionic radii as a function of nominal 3d electron counts. Note that the axis of the ionic radii is plotted inversely. b Negative correlation between RIXS 3D1 energy and TM (and Al3+) ionic radii in perovskite oxides and Ruddlesden-Popper La2CuO4. We define the error bars as three times the standard errors80 obtained from the model fits. Dashed linear regression line serves as a guide to the eye. High-spin ionic radii are selected for panel (b).