Local Structure and Spin Transition in Fe2O3 Hematite at High-Pressure

The pressure evolution of the local structure of Fe2O3 hematite has been determined for the first time by extended x-ray absorption fine structure up to 79 GPa. The comparison to the different high-pressure forms proposed in the literature suggests that the orthorhombic structure with space group Aba2 is the most probable. The crossover from Fe high-spin to low-spin states with pressure increase has been monitored from the pre-edge region of the Fe K-edge absorption spectra. The "simultaneous" comparison with the local structural changes allows us to definitively conclude that it is the electronic transition that drives the structural transition and not viceversa

Nanolayered Diamond Sintered Compact Obtained by Direct Conversion from Highly Oriented Graphite under High Pressure and High Temperature

A new type of polycrystalline sintered diamond has been successfully synthesized by direct conversion from highly oriented pyrolytic graphite at 15 GPa and 2300°C. It is optically transparent and consists entirely of layered nanocrystals (50–100 nm thick) of cubic diamond, which are tightly bound to each other and have strong [111] preferred orientation along the stacking direction. This nanolayered diamond has excellent indentation hardness (~114 GPa in Knoop scale) comparable to the highest values obtained from single crystalline diamond. Furthermore, it is expected to have significantly high wear resistance on both ends of cylindrical sintered compact, since the surfaces are terminated exclusively by the hardest {111} planes of the layered diamond nanocrystals

High-pressure and high-temperature synthesis of heavy lanthanide sesquisulfides Ln2S3 ( Ln=Yb and Lu)

Detailed pressure-temperature phase diagrams of heavy lanthanide sesquisulfides Ln2S3 (Ln = Yb and Lu) have been investigated by in-situ x-ray diffraction experiments under high pressure and high temperature using synchrotron radiation and multi-anvil press. Based on the results of the in-situ observation, the single γ-phase (Th3P4-type structure, I3d) samples of Ln2S3 (Ln = Yb and Lu) have been synthesized under high pressure. The physical properties of the compounds were studied by electrical resistivity, specific heat, and magnetic susceptibility measurements between 2 K and 300 K

Pressure-induced structural changes in α-MoO3 probed by X-ray absorption spectroscopy

The authors are grateful to Prof. Alain Polian for providing NDAC cell. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. The work was supported by philanthropist MikroTik and administrated by the University of Latvia Foundation.Energy-dispersive X-ray absorption spectroscopy at the Mo K-edge was used to study pressure-induced (up to 36 GPa) changes in the local atomic structure of 2D layered oxide α-MoO3. A linear combination analysis based on the low and high-pressure X-ray absorption near edge structure (XANES) spectra shows clear evidence of two high-pressure phases, existing at 18-25 GPa and above 32 GPa. The first transition is due to gradual decrease of the interlayer gap, whereas the second one - to its collapse and oxide structure reconstruction. The local atomic structure around molybdenum atoms at 0.2, 18.5 and 35.6 GPa was determined from the extended X-ray absorption fine structure (EXAFS) using reverse Monte Carlo calculations.Project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Recent progress in high-pressure X-ray absorption spectroscopy studies at the ODE beamline

I.J. and A.K. are grateful to the Latvian Council of Science project no. lzp-2018/2-0353 for financial support. The research leading to these results has been partially supported by the project CALIPSOplus under the Grant Agreement No. 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020.High pressure energy-dispersive X-ray absorption spectroscopy is a valuable structural technique, especially, when combined with a nano-polycrystalline diamond anvil cell. Here we present recent results obtained using the dispersive setup of the ODE beamline at SOLEIL synchrotron. The effect of pressure and temperature on the X-ray induced photoreduction is discussed on the example of nanocrystalline CuO. The possibility to follow local environment changes during pressure-induced phase transitions is demonstrated for α-MoO (Formula presented.) based on the reverse Monte Carlo simulations.Horizon 2020 project CALIPSOplus under the Grant Agreement No. 73087; Latvian Council of Science project no. lzp-2018/2-0353; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Data-driven Exploration of New Pressure-induced Superconductivity in PbBi2_2Te4_4 with Two Transition Temperatures

Candidates compounds for new thermoelectric and superconducting materials, which have narrow band gap and flat bands near band edges, were exhaustively searched by the high-throughput first-principles calculation from an inorganic materials database named AtomWork. We focused on PbBi$_2$Te$_4$ which has the similar electronic band structure and the same crystal structure with those of a pressure-induced superconductor SnBi2Se4 explored by the same data-driven approach. The PbBi$_2$Te$_4$ was successfully synthesized as single crystals using a melt and slow cooling method. The core level X-ray photoelectron spectroscopy analysis revealed Pb2+, Bi3+ and Te2- valence states in PbBi$_2$Te$_4$. The thermoelectric properties of the PbBi$_2$Te$_4$ sample were measured at ambient pressure and the electrical resistivity was also evaluated under high pressure using a diamond anvil cell with boron-doped diamond electrodes. The resistivity decreased with increase of the pressure, and two pressure-induced superconducting transitions were discovered at 3.4 K under 13.3 GPa and at 8.4 K under 21.7 GPa. The data-driven approach shows promising power to accelerate the discovery of new thermoelectric and superconducting materials