Effect of copper doping on kinetic coefficients and their anisotropy in PbSb2Te4

Abstract

In anisotropic PbSb2Te4 and PbSb2Te4:Cu single crystals, nine main independent components of the Hall, electrical-conductivity, thermopower, and Nernst-Ettingshausen effects and their anisotropy in the range 77–450 K have been studied. PbSb2Te4 single crystals exhibit a high hole concentration (p ≈ 3 × 1020 cm−3). Copper exhibits a donor effect and significantly (approximately by a factor of 2) reduces the hole concentration in PbSb2Te4. The temperature dependences of the kinetic coefficients, except for the Hall effect, have a form typical of the one-band model. The significant anisotropy of the Hall coefficient R 123/R 321 ≈ 2 at low temperatures corresponds to the multi-ellipsoid model of the energy spectrum of holes in PbSb2Te4. An important feature of the data on transport phenomena is the high thermopower anisotropy (ΔS ≈ 60–75 μV/K) in the mixed conductivity region caused by the mixed scattering mechanism. Data on the anisotropy of the transverse Nernst-Ettingshausen effect confirm the mixed mechanism of hole scattering; in the cleavage plane, scattering at acoustic phonons dominates, while in the trigonal axis direction, impurity scattering appears significant. Doping with copper enhances the role of impurity scattering in the direction of the trigonal axis c 3; as a result, two components of the Nernst-Ettingshausen tensor Q 321 and Q 132 in the PbSb2Te4:Cu single crystal are positive at low temperatures, whereas, in the undoped crystal, only the Q 321 component is positive.