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A thermodynamic model which explain the dynamics of hydrate decomposition temperature in phase equilibria [H.sub.2]-C[H.sub.4]-[H.sub.2]O system is described.

Dissociation temperatures of gas hydrate formed in the ethane-water system are studied at pressures up to 1500 MPa. In situ neutron diffraction analysis and X-ray diffraction analysis in a diamond anvil cell showed that the gas hydrate formed in the ethane-water system at 340, 700, and 1840 MPa and room temperature belongs to the cubic structure I (CS-I).

The compositions and properties of argon and methane high-pressure gas hydrates were directly determined. The samples of the gas hydrates were prepared under high-pressure conditions and quenched at 77 K.

The pressure (P) dependencies of both the thermopower (Seebeck effect) S and the electrical resistance (R) for p-type single crystals of Bi2Te3 and indium-doped bismuth telluride (InxBi2-xTe3,0.04≤x≤0.10) are reported on a pressure range of 0–8.5 GPa. The thermoelectric power factor (efficiency) (æ=S2/R) exhibits two maxima: the first one near ∼1 GPa and the second near ∼2.5–4.5 GPa. These features evidence a giant increase in the power factor by a factor of ∼10. Possible values of the dimensionless figure of merit under pressure are also estimated. The maxima are explained in terms of pressure-driven changes in an electron structure. The second feature may be also addressed to an intermediate high-pressure phase detected in x-ray diffraction studies. [ABSTRACT FROM AUTHOR]

The studies related to the pressure (P) dependencies of both the thermopower S and the electrical resistance (R) for p-type single crystals of [Bi.sub.2][Te.sub.3] and indium-doped bismuth telluride are reported. The giant increase in the power factor by a factor of 10 is explained in terms of pressure-driven changes in an electron structure.

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. [ABSTRACT FROM AUTHOR]