Physical properties of the poly-vanadium-molybdenum acid xerogels

Measurements of charge transport in thin layers of poly-vanadium-molybdenum acid, de scribed by the general formula H2V12-xMoxO31 +/- y . nH(2)O where x = 0, 0.5, 1, 2 and 3, are presented. From the results of three experiments (conductance and capacitance frequency dependencies, Cole-Cole diagrams, and transient current measurements) on charge transport in H2V12-xMoxO31 +/- y . nH(2)O thin films, the mobilities of the carriers along (mu(parallel to)) and across (mu(perpendicular to)) V-O-Mo layers were determined: mu(parallel to) approximate to 10(-8) m(2)/V s, mu(perpendicular to) = 10(-12) m(2)/V s. The carrier concentration is n approximate to 10(25) m(-3). The isotropy of the conductivity of poly-vanadium-molybdenum acid is caused by the mobility anisotropy. The frequency dependencies of the conductance and capacitance of the xerogels were described by a model which took into account the interaction between the drift charge and its environment. The conductance and capacitance of the investigated compounds depends on the relative humidity of the surrounding atmosphere when the amount of molybdenum in the materials is not equal to zero. (C) 1998 Elsevier Science B.V. All rights reserved.