Bi1−xSbx solid solutions have attracted much attention as promising low-temperature thermoelectric materials. Previously, we observed distinct extrema in the isotherms of the transport and mechanical properties of polycrystalline Bi1−xSbx and attributed their presence to the transition from diluted to concentrated solid solutions and to the reconstruction of the energy band structure under increasing Sb concentration. The goal of the present work is a detailed study of the concentration dependences of the thermal conductivity λ for Bi1−xSbx polycrystalline solid solutions (x = 0 to 0.09) in the temperature range of 170 K to 300 K. It is established that the λ(x) dependences exhibit a nonmonotonic behavior: in certain concentration ranges an anomalous increase in λ with increasing x is observed. It is shown that the concentration dependences of the thermoelectric figure of merit calculated on the basis of the measured λ values are also nonmonotonic. The obtained data represent additional evidence in favor of our assumptions stated earlier about a significant effect of electronic phase transitions observed in Bi1−xSbx solid solutions on the concentration dependences of their thermoelectric properties. These results should be taken into account when developing new Bi1−xSbx-based materials.

An X-ray study of Bi1-xSbx alloys in the concentration range x = 0 – 0.1 was carried out. It was established that up to an Sb concentration x ~ 0.02, the unit cell parameters (a, c) decrease linearly with increasing concentration, and the diffraction linewidth increases. In the concentration interval of x = 0.025 – 0.1 the a(x) and c(x) curves noticeably deviate from the Vegard straight line, with maximum deviations corresponding to the compositions at which the transition to a gapless state and the energy band inversion occurs (x = 0.03 – 0.035) and the semimetal-semiconductor transition (x = 0.06 – 0.07) takes place. In the indicated concentration regions, and also in the interval x = 0.005 – 0.01, a decrease in the X-ray diffraction line width is observed. It is suggested that the structural instability occurring in these special concentration ranges in Bi1-xSbx solid solutions is connected with changes in the electron spectrum under the percolation transition, the transition into a gapless state and band inversion and under a semimetal – semiconductor transition