ELECTRONIC INSTABILITIES IN THE QUASI-2-DIMENSIONAL METALLIC OXIDE KXP4W8O32

Large single crystals of KxP4W8O32 with x = 1.00(5), x = 1.05(5) and x = 1.30(9) were prepared by the chemical vapour transport technique an d electron transport properties were investigated. Thermal variation o f the resistivity between 300 K and 4.2 K shows metallic behaviour wit h anomalies whose onset temperature T-p depends on the potassium conte nt x: T-p = 135 K for x = 1.00, T-p = 150 K for x = 1.05 and T-p = 170 K for x = 1.30. Anomalies can also be observed in the thermal depende nce of the thermopower. A conventional metal behaviour is thus observe d above T-p while a strong deviation from linearity is observed below T-p with a change of sign from negative to-positive which depends on t he x value. The magnetic field dependence of the resistivity has been studied in the low-temperature state for x = 1.30 and shown to be stro ngly correlated with the orientation of the magnetic field with respec t to the conducting plane. The results are explained on the basis of P eierls instabilities and charge density waves (CDW) gap openings with electron and hole pockets which compete on the Fermi surface.