Theoretical and experimental evidence of a site-selective Mott transition in Fe2O3 under pressure

We provide experimental and theoretical evidence for a novel type of pressure-induced insulator-metal transition characterized by site-selective delocalization of the electrons. M\"ossbauer spectroscopy, X-ray diffraction and electrical transport measurements on Fe$_2$O$_3$ to 100 GPa, along with dynamical mean-field theory (DFT+DMFT) calculations, reveal this site-selective Mott transition between 50 and 68 GPa, such that the metallization can be described by (^\rm{VI}Fe$^{3+\rm{HS}}$)$_2$O$_3$ [$R\bar{3}c$ structure] $\overrightarrow{\tiny\rm{50~GPa}}$ (^\rm{VIII}Fe$^{3+\rm{HS~VI}}$Fe^\rm{M})O$_3$ [$P2_1/n$ structure] $\overrightarrow{\tiny\rm{68~GPa}}$ (^\rm{VI}Fe^\rm{M})$_2$O$_3$ [$Aba2$ structure]. Within the $P2_1/n$ crystal structure, characterized by two distinct coordination sites (VI and VIII), we observe equal abundances of ferric ions (Fe$^{3+}$) and ions having delocalized electrons (Fe^\rm{M}), and only at higher pressures is a fully metallic $Aba2$ structure obtained, all at room temperature. The transition is characterized by delocalization/metallization of the $3d$ electrons on half the Fe sites, with a site-dependent collapse of local moments. Above $\sim$50 GPa, Fe$_2$O$_3$ is a strongly correlated metal with reduced electron mobility (large band renormalizations) of m*/m$\sim$4 and 6 near the Fermi level. Upon decompression, we observe a site-selective (metallic) to conventional Mott insulator phase transition (^\rm{VIII}Fe$^{3+\rm{HS~VI}}$Fe^\rm{M})O$_3$ $\overrightarrow{\tiny\rm{50~GPa}}$ (^\rm{VIII}Fe$^{3+\rm{HS~VI}}$Fe$^{3+ \rm{HS}}$)O$_3$ within the same $P2_1/n$ structure, indicating a decoupling of the electronic and lattice degrees of freedom, characteristic of a true Mott transition. Our results show that the interplay of electronic correlations and lattice may result in rather complex behavior of the electronic structure and magnetic state.Comment: 18 pages, 5 figure

Phase transitions and spin-state of iron in FeO at the conditions of Earth's deep interior

Iron-bearing oxides undergo a series of pressure-induced electronic, spin and structural transitions that can cause seismic anomalies and dynamic instabilities in Earth's mantle and outer core. We employ x-ray diffraction and x-ray emission spectroscopy along with state-of-the-art density functional plus dynamical mean-field theory (DFT+DMFT) to characterize the electronic structure and spin states, and crystal-structural properties of w\"ustite (Fe$_{1-x}$O) -- a basic oxide component of Earth's interior -- at high pressure-temperature conditions up to 140 GPa and 2100 K. We find that FeO exhibits complex polymorphism under pressure, with abnormal compression behavior associated with electron-spin and crystallographic phase transitions, and resulting in a substantial change of bulk modulus. Our results reveal the existence of a high-pressure phase characterized by a metallic high-spin state of iron at about the pressure-temperature conditions of Earth's core-mantle boundary. The presence of high-spin metallic iron near the base of the mantle can significantly influence the geophysical and geochemical properties of Earth's deep interior.Comment: 5 figures, with supplementary material

Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700