PRESSURE EFFECT ON CRYSTAL STRUCTURE OF BISMUTH TUNGSTATE Bi2WO6

The structural phase transitions in Bi2WO6 have been investigated by neutron diffraction and Raman spectroscopy at high-pressures. Two phase transitions under pressure were ob-served in the pressure range up to 7 GPa, which are associated with rotations and tilts of the octahedral WO6.The work was supported by the Russian Foundation for Basic Research, grant RFBR N19-52-45009 IND_a

Pressure-induced spin state crossover in layered cobaltite LaSrCoO<inf>4</inf>

© 2019 Elsevier B.V. The crystal structure of the tetragonal layered cobalt oxide LaSrCoO4 has been studied by means of neutron diffraction at high pressures up to 5.8 GPa in temperature range 7–300 K. The pressure and temperature behaviour of the lattice parameters, including lattice parameters, unit cell volume, and interatomic bond lengths, have been obtained. The anisotropic compression of lattice parameters as well as Co-O bond lengths of the oxygen octahedra have been revealed. The anomalous thermal volume expansion at high pressure are observed, indicative for the pressure induced spin state crossover of Co3+ ions from the mixed low spin – high spin (LS + HS) state at room temperature towards the low spin (LS) ground state. The structural mechanisms of the spin state crossover are discussed

Phase composition and its spatial distribution in antique copper coins: Neutron tomography and diffraction studies

The chemical and elementary composition, internal arrangement, and spatial distribution of the components of ancient Greek copper coins were studied using XRF analysis, neutron diffraction and neutron tomography methods. The studied coins are interesting from a historical and cultural point of view, as they are “Charon’s obol’s”. These coins were discovered at the location of an ancient Greek settlement during archaeological excavations on the “Volna-1” necropolis in Krasnodar Region, Russian Federation. It was determined that the coins are mainly made of a bronze alloy, a tin content that falls in the range of 1.1(2)–7.9(3) wt.%. All coins are highly degraded; corrosion and patina areas occupy volumes from ~27 % to ~62 % of the original coin volumes. The neutron tomography method not only provided 3D data of the spatial distribution of the bronze alloy and the patina with corrosion contamination inside coin volumes, but also restored the minting pattern of several studied coins. Taking into account the obtained results, the origin and use of these coins in the light of historical and economic processes of the Bosporan Kingdom are discussed

Pressure-induced spin state crossover in layered cobaltite LaSrCoO<inf>4</inf>

© 2019 Elsevier B.V. The crystal structure of the tetragonal layered cobalt oxide LaSrCoO4 has been studied by means of neutron diffraction at high pressures up to 5.8 GPa in temperature range 7–300 K. The pressure and temperature behaviour of the lattice parameters, including lattice parameters, unit cell volume, and interatomic bond lengths, have been obtained. The anisotropic compression of lattice parameters as well as Co-O bond lengths of the oxygen octahedra have been revealed. The anomalous thermal volume expansion at high pressure are observed, indicative for the pressure induced spin state crossover of Co3+ ions from the mixed low spin – high spin (LS + HS) state at room temperature towards the low spin (LS) ground state. The structural mechanisms of the spin state crossover are discussed

Pressure-induced structural phase transitions in bismuth tungstate Bi<inf>2</inf>WO<inf>6</inf>

The pressure-induced structural phase transitions in bismuth tungstate Bi2WO6 have been studied using neutron diffraction and Raman spectroscopy at high pressures up to 7 and 30GPa, respectively. A rich structural polymorphism was revealed. At P ≃ 3.5GPa a phase transition from the initial orthorhombic phase of P21 ab symmetry to an orthorhombic phase of B2cb symmetry was observed. This transition is caused by the complex spatial rotation of the WO6 octahedra. A subsequent isostructural phase transition to another orthorhombic phase of B2cb symmetry was detected at P ≃ 5.9GPa, accompanied by changes in both the mutual rotation and tilting of the oxygen octahedra with respect to the crystal b axis. Two more pressure-induced phase transitions in Bi2WO6 at high pressures of 11.5 and 20GPa were observed in the Raman spectra. These pressure-driven phase transitions in bismuth tungstate are accompanied by anomalies in the pressure dependences of the unit-cell parameters, bond lengths and angles, and in the vibrational modes