Pressure-induced high-spin/low-spin disproportionated state in the Mott insulator FeBO3

The pressure-induced Mott insulator-to-metal transitions are often accompanied by a collapse of magnetic interactions associated with delocalization of 3d electrons and high-spin to low-spin (HS-LS) state transition. Here, we address a long-standing controversy regarding the high-pressure behavior of an archetypal Mott insulator FeBO3 and show the insufficiency of a standard theoretical approach assuming a conventional HS-LS transition for the description of the electronic properties of the Mott insulators at high pressures. Using high-resolution x-ray diffraction measurements supplemented by Mössbauer spectroscopy up to pressures ~ 150 GPa, we document an unusual electronic state characterized by a “mixed” HS/LS state with a stable abundance ratio realized in the R3 ¯ c crystal structure with a single Fe site within a wide pressure range of ~ 50–106 GPa. Our results imply an unconventional cooperative (and probably dynamical) nature of the ordering of the HS/LS Fe sites randomly distributed over the lattice, resulting in frustration of magnetic moments. © 2022, The Author(s).EAR-1634415; U.S. Department of Energy, USDOE: DE-FG02-94ER14466; Office of Science, SC: DE-AC02-06CH11357; Argonne National Laboratory, ANL; University of Chicago; Israel Science Foundation, ISF: 1189/14, 1552/18, 1748/20; Helmholtz Association; 122021000039-4The authors would like to thank Dr. A. Chumakov (ESRF, Grenoble, France, Kurchatov Institute, Moscow, Russia) and Dr. G. Smirnov (Kurchatov Institute, Moscow, Russia) who provided us by high-quality single crystals of FeBO, Prof. L. Dubrovinsky and Prof. D. I. Khomskii for valuable discussions, Dr. V. Prakapenka and Dr. I Kantor for experimental assistance with the facilities of the 13ID-D GSECARS beamline of APS and Dr. S. Clark for experimental assistance with the facilities of the beam line 12.2.2 at ALS, Berkeley. We are grateful also to the team of the ID-27 beamline of the European Synchrotron Radiation Facility, Grenoble, for assisting with the powder XRD measurements. A few Mössbauer spectrum at 115 and 140 GPa were collected at the ID-18 beamline of the European Synchrotron Radiation Facility. We are grateful to Dr. D. G. Merkel, Dr. R. Rüffer and Dr. A. Chumakov for their assistance in using beamline ID-18 and Dr. G. Hearne and Dr. E. Carleschi for assisting with the SMS measurements. This research was supported by Israeli Science Foundation (Grants No. 1189/14, No. 1552/18 and No. 1748/20). I.L. acknowledges support by the state assignment of Minobrnauki of Russia (theme “Electron” No. 122021000039-4). Portions of this work were performed at GeoSoilEnviroCARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. GeoSoilEnviroCARS is supported by the National Science Foundation–Earth Sciences (EAR-1634415) and Department of Energy– GeoSciences (DE-FG02-94ER14466). This research also used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at P02.2 station of PETRA-III, DESY. 3The authors would like to thank Dr. A. Chumakov (ESRF, Grenoble, France, Kurchatov Institute, Moscow, Russia) and Dr. G. Smirnov (Kurchatov Institute, Moscow, Russia) who provided us by high-quality single crystals of FeBO3 , Prof. L. Dubrovinsky and Prof. D. I. Khomskii for valuable discussions, Dr. V. Prakapenka and Dr. I Kantor for experimental assistance with the facilities of the 13ID-D GSECARS beamline of APS and Dr. S. Clark for experimental assistance with the facilities of the beam line 12.2.2 at ALS, Berkeley. We are grateful also to the team of the ID-27 beamline of the European Synchrotron Radiation Facility, Grenoble, for assisting with the powder XRD measurements. A few Mössbauer spectrum at 115 and 140 GPa were collected at the ID-18 beamline of the European Synchrotron Radiation Facility. We are grateful to Dr. D. G. Merkel, Dr. R. Rüffer and Dr. A. Chumakov for their assistance in using beamline ID-18 and Dr. G. Hearne and Dr. E. Carleschi for assisting with the SMS measurements. This research was supported by Israeli Science Foundation (Grants No. 1189/14, No. 1552/18 and No. 1748/20). I.L. acknowledges support by the state assignment of Minobrnauki of Russia (theme “Electron” No. 122021000039-4). Portions of this work were performed at GeoSoilEnviroCARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. GeoSoilEnviroCARS is supported by the National Science Foundation–Earth Sciences (EAR-1634415) and Department of Energy– GeoSciences (DE-FG02-94ER14466). This research also used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at P02.2 station of PETRA-III, DESY

Deadwood in the oak forests of the Left Bank Forest-steppe of Ukraine

Deadwood is an important component of forest ecosystems, and difference in the deadwood carbon stock depends on many variables including forest management. The aim of our study was to determine the patterns of formation of deadwood stocks in oak (Quercus robur L.) forests in the Left Bank Forest-steppe of Ukraine. As an outcome of the research, the data on deadwood parameters were obtained. The growth characteristics and coarse woody debris (CWD) characteristics were measured on intensive monitoring and inventory plots. Assessment of morphometric parameters of the CWD in oak stands was carried out by measuring diameters at top and bottom cut and length; to determine the carbon content, deadwood density was used. The distribution of deadwood by tree species, sizes and stages of decomposition was defined. The stock of dead trees (snags) in oak forest is 15.2 m3/ha and that of logs is 21.5 m3/ha. The carbon accumulation in oak forest stands in the Left Bank Forest-steppe of Ukraine was 3.4 and 4.5 t C/ha in dead trees and logs, respectively. The dynamics of deadwood stocks according to the results of repeated observations was given