Anomalous electrical and magnetic behavior in (PO2)4(WO3)2m (m=4).

Abstract

Single crystals of ${\mathrm{P}}_{4}$${\mathrm{W}}_{8}$${\mathrm{O}}_{32}$ {(${\mathrm{PO}}_{2}$${)}_{4}$(${\mathrm{WO}}_{3}$${)}_{2\mathit{m}}$, m=4} were prepared by chemical-vapor transport technique with KI as the transport agent. The temperature dependence of electrical resistivity in the range \ensuremath{\sim}2--300 K shows metallic behavior with two anomalies at \ensuremath{\sim}60 and \ensuremath{\sim}85 K. The room-temperature resistivities along the long- and short-plate axis of a single crystal (a and b axes) are 3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ and 2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ \ensuremath{\Omega} cm while that perpendicular to the crystal plate (c axis) is 7\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ \ensuremath{\Omega} cm. The relatively higher conductivities in the crystallographic a-b plane confirm that the compound is a quasi-two-dimensional metal. Seebeck measurement indicates that at room temperature the primary charge carriers are electrons. The magnetic susceptibility is temperature independent down to \ensuremath{\sim}92 K. At \ensuremath{\sim}92 and \ensuremath{\sim}56 K sharp decreases in the susceptibility are observed. The anomalous behavior in the magnetic susceptibility and electrical resistivity of ${\mathrm{P}}_{4}$${\mathrm{W}}_{8}$${\mathrm{O}}_{32}$ at low temperatures is indicative of the onset of charge-density-wave states and is consistent with the proposed band electronic structure.