High‐pressure thermopower of PbTe‐based compounds

Abstract

In the present paper the thermoelectric properties of p‐type PbTe‐based compounds (Pb1–xGaxTe, Pb1–xSnxTe, Pb1–xSixTe, Pb1–xMnxTe, PbTe1–y, Pb1–yTe) have been investigated at high pressure up to ∼12 GPa. Structural phase transitions from cubic NaCl into orthorhombic GeS structure have been observed with thermoelectric measurements. A low sensitivity of thermoelectric properties to high‐pressure treatment has been found for PbSnTe compounds (x ≈ 0.29). For the rest of the samples with a small content of doping atoms a sign inversion and a following maximum of thermoelectric power S have been established at pressures ∼1–3 GPa. The results obtained show the possibility of improving the thermoelectric figure of merit and effectiveness at moderate pressures for PbTe‐based compounds. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High‐pressure X‐ray diffraction study of ternary and non‐stoichiometric PbTe and PbSe crystals

“…, a heterophase region was found to exist from 6.05 GPa up to 7.82 GPa. Shifts in transition pressures P t of nonstoichiometrics compounds agreed with the thermopower data [13] confirming that excess of Pb decreases P t , while excess of Te increases that in comparison with stoichiometric binary PbTe. According to the thermopower data [13], the beginning of the phase transition in Pb 1-x Mn x Te (x = 0.05) was expected to occur at less pressure than in binary PbTe [6], but this divergence might by explained by a wide pressure step in synchrotron diffraction study (Fig.…”

“…It is remarkably to note that a strong substitution www.pss-b.com by Sn (29 at%) did not result in any significant difference in high-pressure structural behaviour of PbTe. While from the thermopower S study, this composition is a p-type semimetal in the range of 0-15 GPa in contrary to all the others [13], and the phase transition was hardly noticeable by S(P) [13].…”

“…Thus, new phase is formed from NaCl lattice by a distortion resulting in two-fold enlargement in period. So, a mechanism of the transition is probably a Peierls distortion [11,12,22,23], and an energetic profit during the transformation is achieved by a splitting of conduction band and formation of forbidden gap at Fermi level [13].…”

“…Due to the low transition pressures, this phase is promising for electronic applications, for example, for thermoelectric generators with the improved thermoelectric parameters [13]; this circumstance motivated investigation of its structural properties. The transformation from NaCl into the high-pressure phase is accompanied by both a sharp change of the electrical resistivity [8,9,11,12] and abrupt drop of the thermopower [11][12][13] in PbS and PbSe single crystals, while only by the slight changes in PbTe [11][12][13]. Both the thermomagnetic longitudinal and transverse Nernst-Ettingshausen effects inverted their signs during the above transition in PbSe, pointing to a change of sign of scattering parameter of charge carriers [15,16], while, no inversion was registered in PbTe [15,16].…”

“…Under pressure these minerals undergo the structural transitions from ambient fcc (face-centred-cubic) NaCl lattice (space group Fm3m) to an intermediate high-pressure phase above P ~ 2.5-6 GPa, and then above P ~ 12-21 GPa to the metal bcc (bodycentred-cubic) CsCl lattice [4]. The above transformations were already investigated by a set of different techniques, including structural X-ray diffraction [4][5][6], Raman scattering [7], the electrical resistance [8][9][10][11][12], thermopower [11][12][13], the Hall effect [14], and thermomagnetic Nernst-Ettigshausen effects [15,16]. Meanwhile, until present a lattice of the intermediate high-pressure phase was not exactly detected [4,5].…”