Substitutional effects on the electrical properties of the purple bronze Li_0.9Mo₆O₁₇

Dopant-level substitution of tungsten for molybdenum in Li_0.9Mo_6-xW_xO₁₇ solid solutions is shown to have a large effect on the electrical transport properties, which might be attributed to W interfering with the overlap of t_2g 4d Mo and π 2p orbitals forming the conduction band. With increasing concentration of W, the metal-to-metal transition broadens and shifts to higher temperature. At ∼6 at.% W content the material becomes semiconducting. Effects on the electronic properties are much less dramatic by alkali metal substitution in (Na_1-xLi_x)_0.9Mo₆O₁₇ alloys, since the alkali metals are only indirectly involved in the formation of the band structure. With x = 0, 0.25 and 0.5 the electrical resistivity behaves similar to Na_0.9Mo₆O₁₇. At x = 0.75 the electrical transport properties are nearly identical to that Li_0.9Mo₆O₁₇ and the supercond uctivity at 2 K is still observed.