Electronic instabilities and localization effects in the quasi-two-dimensional monophosphate tungsten bronzes (PO2)(4)(WO3)(2m) and KxP4W8O32

The monophosphate tungsten bronzes (PO2)(4)(WO3)(2m) with pentagonal tunnel s are quasi-two-dimensional conductors that show charge density wave type e lectronic instabilities. These series of compounds provide a model system w here the lo low-dimensional character and the average electron concentratio n are functions of the m parameter, The low m compounds (m = 4, 6) show con ventional charge density wave instabilities. The NI = 5 compound exists wit h two different crystal structures and shows instabilities with slightly di fferent properties. We report measurements of transport properties for the compounds m = 5, 7, 8, 9, We show that, for m > 7, these compounds exhibit an upturn of resistivity and field dependence of the magnetoresistance char acteristic of quantum interference effects. We also report transport proper ties of the compounds KxP4W8O32 with pseudo-hexagonal tunnels that show ele ctronic instabilities with critical temperatures depending on x, (C) 1999 A cademic Press.