We report the results of a study of the thermoelectric power (Seebeck effect), the electrical resistivity, X‐ray diffraction, and Raman spectroscopy under high pressure (P) to 15 GPa for binary and tin‐doped lead selenide (PbSe and Pb1–x Snx Se (x = 0.125)). The gathered data were inconsistent with previous models suggesting only one intermediate phase between the ambient NaCl (B1) lattice and a high‐pressure metal CsCl (B2) lattice. Furthermore, the data hint at the existence of two competing intermediate phases. From the thermopower we established that a phase that is characterized by n‐type conductivity is dominating, while the other one – of p‐type conductivity is probably optional. The electrical conductivity in both of the phases is semiconducting. In the X‐ray diffraction studies in one of the three investigated samples of Pb0.875Sn0.125Se we could refine a pattern of the intermediate phase taken at ∼9.5 GPa in the Cmcm space group. This corresponds to the symmetry of earlier proposed structural types of TlI and CrB. The patterns of the intermediate phase in the two other samples show additional strong reflexes that are not related to either the NaCl or the CsCl lattices. This presents evidence of the presence of one more undetermined phase. The Raman spectra of the intermediate phase showed a dependence on a pressure‐transmitting medium (methanol‐ethanol or KCl). The pressure‐driven NaCl → CsCl transition and a pressure dependence of the semiconductor energy gap of PbSe are compared with those of other lead salts, namely, PbTe and PbS (galena). It is surmised that there is no interrelation between the closure of the energy gap at the NaCl phase and the phase transition to the intermediate phase. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In this paper the technique of thermoelectric measurements at high pressure was applied for characterization of semiconductor microsamples based on lead chalcogenide compounds (p-PbSe, n-Pb 1−x Sn x Se). The Raman scattering technique at ambient pressure was used as an alternative tool for testing of the samples. Raman measurements have revealed broad peaks at 135 and 265 cm −1 for PbSe and Pb 1−x Sn x Se. Analogous spectra were obtained for PbS, and PbTe-based ternary compounds at higher and lower frequencies, respectively. The peaks have been attributed to the first-and second-order Raman modes. From resistivity and thermoelectric power data the linear decrease in the pressure of the NaCl → GeS structural phase transition with increasing Sn content has been established and the thermopower of high-pressure GeS phases have been determined. Thermoelectric properties of the samples at high pressure have shown high sensitivity to a small variation in the composition of the ternary Pb 1−x Sn x Se compounds, which makes it possible to distinguish semiconductor microsamples whose compositions are very similar.

We suggest a method for detection of highly conductive surface electron states including topological ones. The method is based on measurements of the photoelectromagnetic effect using terahertz laser pulses. In contrast to conventional transport measurements, the method is not sensitive to the bulk conductivity. The method is demonstrated on an example of topological crystalline insulators Pb1−xSnxSe. It is shown that highly conductive surface electron states are present in Pb1−xSnxSe both in the inverse and direct electron energy spectrum.

No abstract

The crystal structure, Sn and V distribution over the length of single crystal ingots, and galvano magnetic effects in low magnetic fields (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) in Pb 1 -x -y Sn x V y Te alloys (x = 0.05-0.21, y ≤ 0.015) are studied. It is shown that all the samples are single phase, while the Sn and V concentrations exponentially increase from the beginning to the end of the ingots. Upon doping with V, a decrease in the con centration of free holes and a metal-insulator transition are found. They are related to the appearance of a deep impurity level of V in the band gap, electron redistribution between the level and the valence band, and pinning of the Fermi level to the impurity level. The shift rate of the V level relative to the conduction band bottom is determined and a diagram of the reconstruction of the electronic structure of the Pb 1 -x -y Sn x V y Te alloy upon varying the host composition is suggested.