Electrical Properties of Some Dilute Cubic Sodium Tungsten Bronzes

Abstract

The preparation and electrical properties are described for cubic Na_xWO₃ single crystals of the compositions x=0.363, 0.291, and 0.234. Specimens were prepared by diffusing sodium from single crystals of Na_0.687WO₃. The composition and homogeneity of the crystals were established by x‐ray powder and back‐reflection Laue photographs. The electrical resistivity‐temperature plots show a more complex electronic behavior than had been expected for dilute Na_xWO₃ on the basis of earlier work; Na_0.291WO₃ and Na_0.234WO₃ exhibit resistivity minima at about 150° and 320°K, respectively, with characteristics similar to that of degenerate semiconductors. A polycrystalline sample of Na_0.025WO₃, having a room‐temperature resistivity of 3×10^—3 ohm cm and a Seebeck coefficient of —270 μv/deg, is also described.