PRESSURE-DEPENDENCE OF THE PEIERLS TRANSITION IN THE QUASI-2-DIMENSIONAL PURPLE BRONZE KMO6O17

The electrical activity and the lattice parameters have been studied a s a function of pressure on the quasi-twodimensional purple bronze KMo 6O17 which shows a Peierls transition towards a commensurate charge de nsity wave state. The Peierls temperature is found to be first slightl y decreased for pressures smaller than 6 kbar, then strongly increased above. This increase is associated to an anomalous contraction of the lattice parameters in the plane of the layers. The corresponding larg e increase of the compressibility above 16 kbar at 300 K is associated to the pretransitional regime of the Peierls transition as a function of pressure. These results are attributed mainly to an improved nesti ng of the Fermi surface under pressure.