Dielectric properties of the low dimensional vanadium oxides Ba2V3O9 and Sr2V3O9

The dielectric response of the low-dimensional vanadium oxides Ba2V3O9 and Sr2V3O9 has been investigated in the frequency range of 20 Hz-1 MHz. At low frequencies the dielectric response is governed by strong relaxation-like features, which we attribute to Maxwell-Wagner type contact contributions. The analysis of the complex dielectric spectra in terms of an equivalent circuit revealed the intrinsic dielectric constant and dc conductivity of these systems. The frequency-dependent ac conductivity in both systems follows the universal dielectric response behaviour, clearly indicating that hopping of localised charge carriers is the dominating charge-transport process. Also, a newly observed dielectric relaxation process in both systems is reported and we find evidence for a phase transition close to 455 K in both materials. (C) 2002 Elsevier Science Ltd. All rights reserved.