A. I. Ancharov

Anomalous compression of scolecite and thomsonite in aqueous medium to 2 GPa

The high-pressure behaviour of fibrous zeolites scolecite and thomsonite in penetrating aqueous medium was studied using in situ synchrotron powder diffraction data from diamond anvil cell. Both zeolites exhibit anomalous compressibility due to an additional pressure-induced hydration of structure channels. At 1.23 GPa, scolecite undergoes transformation to high-hydrated phase, which is expanded by 5.0% as compared to original scolecite due to the increase of zeolitic water content from 3 to 4.6 molecules per formula unit. The compressibility of thomsonite is markedly lower than that reported previously, where a nominally penetrating medium with 6% H2O was used. This indicates to an additional hydration under high pressure, which is confirmed by the observed phase transition in thomsonite. The over-hydration effect in fibrous zeolites seems to largely depend on partial water pressure in compressing medium.

Enhanced power factor and high-pressure effects in (Bi,Sb)2(Te,Se)3 thermoelectrics

We investigated the effects of applied high pressure on thermoelectric, electric, structural, and optical properties of single-crystalline thermoelectrics, Bi2Te3, BixSb2−xTe3 (x = 0.4, 0.5, 0.6), and Bi2Te2.73Se0.27 with the high thermoelectric performance. We established that moderate pressure of about 2–4 GPa can greatly enhance the thermoelectric power factor of all of them. X-ray diffraction and Raman studies on Bi2Te3 and Bi0.5Sb1.5Te3 found anomalies at similar pressures, indicating a link between crystal structure deformation and physical properties. We speculate about possible mechanisms of the power factor enhancement and suppose that pressure/stress tuning can be an effective tool for the optimization of the thermoelectric performance.

Clathrate Hydrates of Sulfur Hexafluoride at High Pressures

The pressure dependence (0.4 Mpa–1.3 GPa) of the hydrate decomposition temperatures in the sulfur hexafluoride-water system has been studied. In addition to the known low-pressure hydrate SF6⋯17H2O of Cubic Structure II, two new high-pressure hydrates have been found. X-ray analysis in situ showed the gas hydrate forming in the sulfur hexafluoride-water system above 50 MPa at room temperature to be of Cubic Structure I. The ability of water to form hydrates whose structures depend on the guest molecule size under normal conditions and at high pressures is discussed.

Pressure-induced phase transition in the cubic ScF3 crystal

Pressure-induced phase transitions in the ScF3 crystal were studied using synchrotron radiation diffraction, polarization microscopy, and Raman spectroscopy. The phase existing in the range 0.6–3.0 GPa is optically anisotropic; its structure is described by space group R3c (Z = 2), and the transition is due to rotation of ScF6 octahedra around a threefold axis. The pressure dependence of the structural parameters and angle of rotation are determined. The number of Raman spectral lines corresponds to that expected for this structure; above the phase transition point, a recovery of soft modes takes place. At a pressure of 3.0 GPa, a transition occurs to a new phase, which remains metastable as the pressure decreases. The results are interpreted using an ab initio method based on the Gordon-Kim approach.

Structure of the intermediate high-pressure phases of ternary lead tellurides

In chambers with diamond anvils, the structure of high-pressure phases of ternary lead tellurides Pb1−xSnxTe (x = 0.29) and Pb1−xMnxTe (x = 0.05) and nonstoichiometric crystals Pb0.55Te0.45, Pb0.45Te0.55 is analyzed by the synchrotron radiation diffraction method at pressures of P up to 14 GPa. The orthorhombic structure of the intermediate high-pressure phase (space group Pnma) is determined for all the samples above 6 GPa. Models of the phase transition in PbTe from the initial rock salt structure to the orthorhombic phase, which constitutes a distorted variant of NaCl, as well as the properties of this phase, are discussed.

Structure and lattice dynamics of the high-pressure phase in the ScF3 crystal

AbstractThe high-pressure phase of the ScF3 crystal has been studied using synchrotron radiation diffraction and Raman scattering. This phase existing in the pressure range 0.6–3.2 GPa is optically anisotropic: its structure is described by space group R

Compressibility and phase transitions of potassium carbonate at pressures below 30 kbar

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Structural features of hydrate forms of iron(III) oxalate

c, Z = 2, and the transition is associated with the rotation of ScF6 octahedra around the threefold axis. The pressure dependences of the lattice parameters and the rotation angle have been determined. The number of lines in the Raman spectrum corresponds to the expected number for this structure; the recovery of soft modes has been observed above the phase transition.