Band Electronic Structure of the Molybdenum Blue Bronze A_0.30MoO₃(A = K, Rb)

The electronic structure of the blue bronze A_0.30MoO₃(A = K, Rb) was examined by performing tight-binding band calculations on a number of model chains and an Moi₀O₃₀slab. When normalized to A₃Mo₁₀O₃₀(i.e., half the unit cell), the bottom two d-block bands of an Mo₁₀O₃₀slab are partially filled. The Fermi surfaces of these two bands are open along the interchain direction, in agreement with the experimental fact that the blue bronze is a pseudo-one-dimensional metal with good electrical conductivity along the chain direction b. The Fermi surfaces of the two bands are curved due to interactions between adjacent Mo₁₀O₃₂chains, but the curvatures of the Fermi surfaces are opposite for the two bands. Thus the two pieces of the first-band Fermi surface are nested to those of the second-band Fermi surface by a single wave vector q_b≃ 0.75b*, which explains why only one charge density wave occurs in the blue bronze. For an Mo₁₀O₃₀slab, the bottom of the third d-block band is calculated to lie above, but very close to, the Fermi level (i.e., 0.012 eV above ef). This feature is responsible for the temperature dependence of q_bin the blue bronze, which increases gradually from-0.72b* at room temperature to-0.75b* below the metal-to-semiconductor phase-transition temperature.