We investigated the effects of applied high pressure on thermoelectric, electric, structural, and optical properties of single-crystalline thermoelectrics, Bi₂Te₃, Bi_xSb_2−xTe₃ (x = 0.4, 0.5, 0.6), and Bi₂Te_2.73Se_0.27 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 Bi_0.5Sb_1.5Te₃ 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.

We propose a model of a thermoelectric module in which the performance parameters can be controlled by applied tuneable stress. This model includes a miniature high-pressure anvil-type cell and a specially designed thermoelectric module that is compressed between two opposite anvils. High thermally conductive high-pressure anvils that can be made, for instance, of sintered technical diamonds with enhanced thermal conductivity, would enable efficient heat absorption or rejection from a thermoelectric module. Using a high-pressure cell as a prototype of a stress-controlled thermoelectric converter, we investigated the effect of applied high pressure on the power factors of several single-crystalline thermoelectrics, including binary p-type Bi ₂ Te ₃ , and multi-component (Bi,Sb) ₂ Te ₃ and Bi ₂ (Te,Se,S) ₃ solid solutions. We found that a moderate applied pressure of a few GPa significantly enhances the power factors of some of these thermoelectrics. Thus, they might be more efficiently utilized in stress-controlled thermoelectric modules. In the example of one of these thermoelectrics crystallizing in the same rhombohedral structure, we examined the crystal lattice stability under moderate high pressures. We uncovered an abnormal compression of the rhombohedral lattice of (Bi _0.25 ,Sb _0.75 ) ₂ Te ₃ along the c -axis in a hexagonal unit cell, and detected two phase transitions to the C2/m and C2/c monoclinic structures above 9.5 and 18 GPa, respectively.

The galvanomagnetic and thermoelectric properties of p-Bi_2−x Sb_xTe_3−y Se_y solid solutions (x≤1.2, y≤0.09) are studied for various carrier concentrations. The degeneracy parameter β_d governing the scattering processes in solid solutions was calculated in terms of the many-valley energy spectrum model. The data on the degeneracy parameter and the Seebeck coefficient α were used to calculate the effective scattering parameter r _eff and the reduced Fermi level η. The parameter r _eff was found to depend on the carrier concentration in the materials studied. The temperature dependences of the effective density-of-states mass m/m ₀ and mobility μ₀ in samples with various carrier concentrations were determined.

The Seebeck coefficient Sand electrical conductivity σ of bismuth-telluride-based alloys with substituents in the Bi and Te sublattices are studied at pressures up to 12 GPa at room...

The galvanomagnetic properties of p-type bismuth telluride heteroepitaxial films grown by the hot wall epitaxy method on oriented muscovite mica substrates have been investigated. Quantum oscillations of the magnetoresistance associated with surface electronic states in three-dimensional topological insulators have been studied in strong magnetic fields ranging from 6 to 14 T at low temperatures. The cyclotron effective mass, charge carrier mobility, and parameters of the Fermi surface have been determined based on the results of analyzing the magnetoresistance oscillations. The dependences of the cross-sectional area of the Fermi surface S(k _F), the wave vector k _F, and the surface concentration of charge carriers n _s on the frequency of magnetoresistance oscillations in p-type Bi₂Te₃ heteroepitaxial films have been obtained. The experimentally observed shift of the Landau level index is consistent with the value of the Berry phase, which is characteristic of topological surface states of Dirac fermions in the films. The properties of topological surface states of charge carriers in p-type Bi₂Te₃ films obtained by analyzing the magnetoresistance oscillations significantly expand fields of practical application and stimulate the investigation of transport properties of chalcogenide films.