Static compression of ?-Fe2O3: linear incompressibility of lattice parameters and high-pressure transformations

Local structure and spin transition inFe2O3hematite at high pressure

“…I, 5th row), independently on whether the Fe-O distances at 2.3Å are included or not. In particular, the static disorder of the nearest-neighbor Fe-O distribution is too large compared to that measured by EXAFS, therefore, in agreement with previous studies [4][5][6]15], we can rule out the GdFeO 3 form as HP structure of Fe 2 O 3 . However, we come to the same conclusion also for the distorted Rh 2 O 3 -II structure, space group Pbcn, which is currently the most accepted HP structure for Fe 2 O 3 [4][5][6].…”

“…At ambient conditions, hematite crystallizes in the rhombohedral corundum-type structure, space group R3c, and is a wide-band antiferromagnetic insulator. By increasing pressure at room temperature, the corundum structure of hematite is progressively distorted and, above ∼50 GPa, a series of physical changes occur [1][2][3][4][5][6][7][8][9][10][11]: the unit cell volume drops down by about 10 %, the crystal symmetry changes completely, the electrical resistivity decreases drastically due to the breakdown of the d-electron correlation (Mott insulator-metal transition), the magnetic moments collapse [transition of iron ions from high-spin (HS) to low-spin (LS) state] and the long-range magnetic order disappears. Besides being interesting from the viewpoint of solid-state physics, the phenomena are also important in geophysics for modeling materials behavior in deep Earth's mantle [12][13][14][15][16].…”

“…From the structural point of view, it was initially proposed that the highpressure (HP) form of Fe 2 O 3 was a GdFeO 3 -type orthorhombic perovskite, containing two different Fe sites with different coordination numbers and characterized by unequal valence states, i.e., Fe 2+ and Fe 4+ [17][18][19]. But a few years later, further investigations established that the HP phase of Fe 2 O 3 is a non-magnetic metallic phase with a single Fe 3+ cation site, and identified as the distorted Rh 2 O 3 -II structure [4][5][6]. However this conclusion cannot be regarded as definitive because not based on x-ray "single-crystal" diffraction data, that provides the most accurate structural refinement, and moreover because certain aspects have been challenged by Badro and co-workers [2].…”

Pressure-induced semiconducting to metallic transition in multilayered molybdenum disulphide

“…The solid line is the fitting result (Fig. 5a) using the third-order Birch-Murnaghan equation of state (BM EoS) 53,54 :…”

Material-Specific Investigations of Correlated Electron Systems

“…A charge gap of 2.0-2.7 eV was inferred from dc conductivity data [19]. Under pressure, a first-order phase transition is observed at approximately 50 GPa at which the specific volume decreases by almost 10% and the crystal symmetry is reduced (to the Rh 2 O 3 -II structure) [20,21,22]. The high-pressure phase is characterized by metallic conductivity and the absence of both magnetic LRO and the HS local moment [20].…”