Thermoelectric power, magnetoresistance of lead chalcogenides in the region of phase transitions under pressure

The longitudinal and transverse thermomagnetic Nernst-Ettingshausen (N-E) effects were measured at ultrahigh pressure up to 20 GPa under closure of semiconductor gap at NaCl- and GeS-type phases of n-PbTe, p-PbSe and p-PbS. Near ∼3 GPa, the maxima of N-E effects and magnetoresistance (and hence of mobility of charge carriers) attributed to gapless state for PbTe and PbSe were established. The reversible sign inversion of transverse N-E effect indicating the change in scattering mechanism of charge carries have been revealed at high pressure phase of PbSe. The lowering of thermomagnetic effects with pressure gave the evidence of indirect semiconductor gap at high pressure GeS-type phases in contrary to NaCl-phases.