Correlation and disorder effects for the electronic transport in the low-dimensional system NaxCa1-xV2O5 and NaxV2O5

The transport properties of extra carriers introduced in the Mott insulator NaV(2)O(5) with coupled V-O-V molecular orbitals have been explored through measurements of the x-ray powder diffraction, electrical resistivities and thermoelectric powers for Na(x)Ca(1-x)V(2)O(5) with 0.83 <= x < 1 and Na(x)V(2)O(5) with 0.8 <= x < 1. These systems have electron and hole carriers for x < 1, respectively. In the vicinity of the average V valence of 4.5, the Mott-type one-dimensional variable-range hopping mechanism for coupled chains may be effective, and a linear relation between the hopping energy and the thermoelectric power is found. The composition dependences of thermoelectric powers are almost understood in terms of the Heikes formula in a strongly correlated region with the number of electrons per coupled orbital. The effects of the electron correlation and the atomic disorder for the transport properties may be closely related to each other.