ANISOTROPIC THERMOPOWER IN THE CHARGE-DENSITY-WAVE QUASI-2-DIMENSIONAL COMPOUNDS (PO2)(4)(WO3)(2M)(M=4, 6)

Thermopower and Hall effect have been measured between 4.2 K and 300 K on the monophosphate tungsten bronzes (PO2)(4)(WO3)(2m) with m = 4 an d 6. The Peierls transitions can be clearly observed. In the normal st ate, both compounds behave as nearly compensated metals in agreement w ith band structure calculations. The anisotropic thermopower found in the charge density wave state of the m = 6 compound gives information on the carrier pockets left by the gap openings along different crysta llographic directions.