Anderson Phase Research Articles

Bulk and surface characterization of some heteropolymolybdates and the products of their reduction and sulfidation

[CoMo6O24H6](NH4)3·7H2O Anderson-type hexamolybdate (as prepared, supported on γ-alumina and after thermal treatment in hydrogen or in a thiophene/hydrogen mixture) has been characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), thermal analysis and X-ray photoelectron spectroscopy (XPS). The Anderson phase also contains Co3+ and Mo6+ species at the surface. After thermal treatment at 773 K in hydrogen and exposure to air at room temperature, MoO3 and CoMoO4 are formed. The XP spectrum of the Anderson phase supported on γ-alumina showed the presence of two Mo6+ species, probably due to the coexistence of the molybdenum contained in the structural framework of the Anderson phase and a species derived from the interaction of the hexamolybdate with γ-alumina. The XP spectrum of the supported Anderson phase after sulfidation revealed the presence of two molybdenum species which could be due to the coexistence of sulfide and oxisulfide phases; in addition, the Mo: Al atomic ratio was increased by sulfidation, suggesting a good dispersion of the MoS2-like layered structure with small crystallite sizes. [AIMo6O24H6](NH4)3· 7H2O treated in hydrogen at 1073 K was also characterized and its XRD pattern showed the presence of metallic molybdenum.

The mobility of a quantum particle in a three-dimensional random potential

Abstract The approximation scheme recently proposed for the dynamical conductivity and density fluctuation spectrum of a quantum particle moving in a random potential is rederived within Mori's formalism. The equations are solved by asymptotic expansions (i) for small coupling to study the corrections to the kinetic equation approach for the mobility, (ii) for strong coupling to analyse the insulator instability caused by increasing spontaneous fluctuations, and (iii) for the regime close to the Anderson phase transition from a state with metallic conductivity to an insulating one. The equations are solved numerically and an extensive discussion of the solutions is presented.