Thermoelectric figure of merit and magnetic field production abilities of “natural” PbBi2(Te1 − xSex)4 + δ and PbBi4(Te1 − xSex)7 + δ nanostructures

Abstract

Layered crystals PbBi₂(Te_{1 − x}Se_x)_{4 + δ} and PbBi₄(Te_{1 − x}Se_x)_{7 + δ} with the stoichiometry deviation toward the excess of chalcogenides (x = 0–0.7; δ = 0–0.1) are synthesized. The obtained compounds are attributed to “natural” Bi₂Te₃-type nanostructures with changed nanoidentity parameters (ξ₁ is the layer package thickness, and ξ₂ = c is the increased lattice period along the trigonal crystal axis). A change in the parameters ξ₁ and ξ₂ amplifies the phonon scattering in the samples, causing low thermal conductivity of the crystal lattice of alloys, which is κ_ph = (4.3–7.2) × 10⁻³ W/(cm K) close to the thermal conductivity of amorphous materials. The presence of finely divided precipitations of the additional phases (δ > 0) favors a decrease in the value of κ_ph. In this case, the lower mobility of electrons μ favors a decrease in the maximum figure of merit values (Z = α₂σ/κ) for the samples in comparison with PbTe and Bi₂Te₃ alloys. At the same time, the low values of κ_ph and Z lead to an increase in the magnetic field production ability of alloys, which attain high values of X = Y/(1 + ZT) > 4–5 (here, Y = ασ/κ). No features of the belonging of the studied materials to a class of 3D “topological insulators” (dielectrics in the bulk and metals on the surface) are found over the temperature range of 77–700 K.