Fig. 3
From: Valence and spin states of iron are invisible in Earth’s lower mantle
X-ray emission Fe Kβ spectra and total spin moment. a XES data for (Mg0.46Fe3+0.53)(Si0.49Fe3+0.51)O3 bridgmanite up to 84.9 GPa at 300 K. All spectra were normalized to area and aligned to position of the main peak. Both the spectra of Fe2O3 and the sample at 1 bar served as the high-spin (HS) reference, while FeS2 at 1 bar was used as the low-spin (LS) reference. The inset shows the difference between the sample spectra and the LS reference FeS2. b The total spin moment (left axis) derived from both integrated absolute difference (IAD, open triangles) and integrated relative difference (IRD, black squares) methods68 as a function of pressure. Error bars were determined by evaluating the difference in calculated spin moment using either Fe2O3 or ambient Mg0.46Fe3+1.04Si0.49O3 sample as the HS standard. The expected spin moment for HS-only configuration is 2.5 (marked by the upper horizontal dashed line), while the B-site spin transition should lower total spin moment to 1.5 (marked by the lower horizontal dashed line). The red open circles are HS fractions of B-site Fe3+ (right axis) derived from equation of state (EoS) under high pressures. Error bars of HS fractions obtained from EoS represent 95% confidence interval in EoS parameters VHS, VLS, KHS, and KLS32. XES and XRD concur that spin transition of B-site Fe3+ is centered at 48–49 GPa at ambient temperature
