Electron transport in carbynes modified under high pressure

The studies of hopping conductivity in carbynes modified under high pressure are reviewed. Experimental data are presented on the dc and ac conductivities, thermopower, magnetoresistance, and Hall effect. The results obtained are discussed within the framework of a model that takes into account the substantially nonuniform distribution and clusterization of sp² bonds in the carbyne sp matrix.     

Structural transformations in liquid,crystalline, and glassy B<Subscript>2</Subscript>O<Subscript>3</Subscript> under high pressure

We present in situ (x-ray diffraction) and ex situ (quenching) structural studies of crystalline, liquid, and glassy B₂O₃ up to 9 GPa and 1700 K, drawing equilibrium and nonequilibrium phase diagrams of B₂O₃. Particularly, we have determined the melting curve, the stability regions for crystalline B₂O₃ I and B₂O₃ II modifications, the regions of transformations, such as densification or crystallization, for both the liquid and glassy states, including the region of sharp first-order-like transition in liquid B₂O₃ to a high-density phase near 7 GPa. Quenching experiments also show that the transition to the high-density liquid can occur at much lower pressures in nonstoichiometric melts with an excess of boron. B₂O₃ is the first glassformer whose transformations in the disordered state have been comparatively studied for both liquid and glassy phases.     

Thermopower of Al1−x Six solid solutions in vicinity of lattice instability

The thermopower coefficient as a function of temperature, S(T), has been measured in nonequilibrium superconductors, such as Al_1−x Six substitutional solid solutions and Al-Si alloys on various decay stages. When aluminum is substituted with silicon, the contribution to the thermopower due to phonon-drag effects, which are dominant in pure aluminum at low temperatures, is suppressed, and low-temperature anomalies in S(T) detected in compositions near lattice instability limit are determined by the diffusion component of the thermopower. The low-temperature anomalies in the thermopower and the notable increase in the coefficient in front of the linear term in S(T) are attributed to effects of thermopower renormalization due to the electron-phonon interaction enhancement with “soft modes” in the face-centered cubic (FCC) lattice of Al_1−x Six solid solutions. The nature of these anomalies in S(T) is analyzed in terms of the Kaiser and Reizer-Sergeev models. Zh. éksp. Teor. Fiz. 113, 339–351 (January 1998)     

Logarithmic Relaxation of the Specific Volume and Optical Properties of GeS2 Densified Glass

Journal of Experimental and Theoretical Physics - The relaxation of the optical absorption edge and of the linear sizes of stoichiometric GeS2 glass densified at a high hydrostatic pressure have...     

High-pressure thermoelectric characteristics of Bi2Te3 semiconductor with different charge carrier densities

The measurements of the absolute values of the thermopower and of the relative electrical resistance have been performed for n type Bi₂Te₃ under hydrostatic pressure up to 9 GPa at room temperature. Under pressures exceeding 5 GPa and up to the phase transition (at 7 GPa), the samples with the charge carrier density below 10^?19 cm^?3 exhibit an anomalous growth of the thermopower. For the purest sample (n = 10^?18 cm^?3), the thermopower is as high as +150 μV/K. The pressure dependence of the electrical resistance for n-Bi₂Te₃ does not exhibit any anomalies up to the pressure corresponding to the phase transition (7 GPa). Thus, the state with the giant thermoelectric efficiency is found in Bi2Te3 under pressure before the phase transition.     

Study of the compressibility of FeSi,MnSi, and CoS<Subscript>2</Subscript> transition-metal compounds at high pressures

Silicides and sulfides of transition metals attract great attention of researchers because of a wide spectrum of interesting magnetic, electronic, and optical properties. The crystal structure of FeSi, MnSi, and CoSi silicides is P2₁3(B20), whereas FeS₂, CoS₂, and MnS₂ sulfides have a structure of pyrite Pa3. Despite the great interest in these systems and the cubic symmetry of crystals, the structure and compressibility of these compounds at high pressures are still insufficiently studied. There is a significant spread (more than a factor of two!) in the bulk modulus and its pressure derivative for a single compound. Most studies were performed under nonhydrostatic conditions. In this work, the compressibility of FeSi and MnSi silicides (at pressures up to 35 GPa) and CoS₂ sulfide (up to 22 GPa) has been studied by the X-ray diffraction method in a diamond anvil cell with the use of helium as the softest pressure-transmitting medium. The values obtained for the bulk modulus and its derivative—B = 178 ±3 GPa and B_p = 5.6 ± 0.5 for FeSi, B = 167 ± 3 GPa and B_p^' = 4.6 ± 0.5 for MnSi, and B = 94 ± 2 GPa and B_p^' = 6.9 ± 0.5 for CoS₂—can be considered as the most reliable and can be used to test numerous theoretical models. The results for the compressibility of FeSi are important for the verification of models of the Earth’s core.