Phase transformation and conductivity in nanocrystal PbS under pressure

The grain-size effect on the phase transition induced by pressure in PbS was studied by in situ high-pressure electrical resistance and synchrotron radiation x-ray powder diffraction measurements. The mean transition pressure of the B1-to-B16 phase transformation was found to be 6.3 +/- 1.3 GPa in 8 +/- 1 nm PbS while it is 3.1 +/- 0.7 GPa for 10 mu m PbS. The resistivity of the B16 PbS phase decreases exponentially with pressure in both samples at ambient temperature. They follow R proportional to exp(-CP), where C=-0.64 GPa(-1) for 10 mu m PbS and C=-0.34 GPa(-1) for 8 +/- 1 nm PbS. These results are discussed in terms of a decrease of energy band gap with increasing pressure. (C) 2000 American Institute of Physics. [S0021-8979(00)02102-2].