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.

Raman spectra of single crystals of lead chalcogenides (PbTe, PbSe, PbS) were studied at room temperature and ambient pressure. The structure of spectra for all compounds is rather similar showing the bands in one-and two-phonon range. Possible spectra identification is discussed.

The effect of pressure and temperature on the Raman-active phonon mode of osmium metal has been investigated for pressures up to 20 GPa and temperatures in the range 10-300 K. Under hydrostatic conditions (He pressure medium) the phonon frequency increases at a rate of 0.73(5) cm −1 /GPa (T = 300 K). A large temperature-induced and wavelength-dependent frequency shift of the phonon frequency is observed, of which only a small fraction can be associated with the thermal volume change. The main contribution to the temperature dependence of the phonon frequency is rather attributed to non-adiabatic effects in the electron-phonon interaction, which explains also the observation of an increasing phonon line width upon cooling. The phonon line width and the pressure-induced frequency shift were found to be unusually sensitive to shear stress.PACS numbers: PACS: 62.50.+p, 78.30.Er, 63.20.Kr, Laser Raman scattering (RS) has been utilized in recent diamond anvil cell studies of the lattice dynamical properties of elemental metals at high pressures. 1,2In metals, phonon RS is essentially restricted to firstorder scattering by zone-center optical phonon modes because of the relatively weak Raman signals. Therefore, it is mainly the elemental hcp metals (having one first-order Raman-active phonon mode) that have been investigated by high-pressure RS with a focus on phonon frequency changes which yield indirect information the pressure/volume dependence of the elastic constant C 44 .The high resolution of RS also allows for an investigation of the electron-phonon interaction which is of specific importance to the lattice dynamics of metals. Motivated by the early Raman studies on elemental metals, 3 the effect of electron-phonon interaction on the longwavelength optical phonon spectrum was studied theoretically. 4 The central result is a prediction of a large non-adiabatic renormalization of the phonon spectrum and a strong dispersion of the optical phonon branch at very small phonon momenta, q < ∼h ω 0 /v F , where ω 0 is the bare phonon frequency and v F the Fermi velocity. At these small momenta, the phonon phase velocity is larger than the electronic one, which leads to a violation of the adiabatic approximation and disappearance of the electron-hole channels for the phonon decay.Most RS studies of elemental metals were conducted at room temperature where the effects of electron-phonon interaction vanish, partly due to the smearing of electronic self-energy effects which depend on details of the electronic structure. There are only a few ambientpressure experimental studies of the temperature and momentum dependences of the non-adiabatic effects in hcp transition metals. 5,6,7,8 These investigations revealed anomalies in the temperature and momentum dependences of the energy and line width of long-wavelength optical phonons. In particular, upon cooling they evidence an unusually large phonon frequency hardening and an anomalous increase of the phonon line width.Osmium is one of the better-investigated examples.Here, a...

The results of transverse magnetoresistance (MR) and Raman spectrum (RS) measurements (in the region 80-160 cm -1 ) of Hg 1-x Te x S crystals (0.04 x 0.6) at room temperature and high pressure P up to 1.6 GPa are presented. The galvanomagnetic measurements show the change of electronic structure and charge carrier concentration as the sulphur content is rising. The increasing of MR under P and, hence, the increase of electron mobility agree with the certain model of electronic structure of gapless semiconductors. Three HgTe-like phonon Raman modes were observed near about 90, 120 and 140 cm -1 , and one mode near 100 cm -1 , which was shifted to lower frequencies in the sulphur-rich samples in accordance with theoretical predictions. At P ¼ 1.6 GPa, above the onset of pressure-induced phase, two a-HgS like peaks near 90 cm -1 were observed.