Dielectric and transport properties of K6[V15As6O42(H2O)•8H2O -: art. no. 064417

The dielectric, transport, and vibrational properties of the polyoxovanadate cluster K-6[V15As6O42(H2O)] center dot 8H(2)O, V-15, have been investigated by ac impedance and Raman scattering techniques. Over a temperature range of 77-300 K, V15 shows an essentially temperature-independent dielectric constant of 6 1, and two independent relaxation mechanisms with activation energies of 0.22 and 0.85 eV, respectively. While the origin of 0.85 eV mode remains unclear, Raman scattering experiments show a series of intramolecular vibrations between 85 and 1000 cm(-1) that we believe contribute to the 0.22 eV mode, as its preexponential factor nu(0) is similar to 10(13) Hz (167 cm(-1)). Resistivity data also reveal that V-15 exhibits thermally activated, semiconductorlike behavior over the 285-325 K temperature range. The activation energy, E-a, of V-15 was 0.2 eV, in reasonable agreement with earlier optical measurements of the band gap similar to 0.5 eV, assuming E-g=2E(a).