TRANSPORT PROPERTIES AND STRUCTURE OF VANADIUM PHOSPHATE GLASSES

The adiabatic hopping model for the electrical conductivity of the vanadium phosphate glasses, V//1// minus //xP//1// minus //xO//5// minus //c/////2, is examined in terms of their structures as derived from recent X-ray studies. These indicate that the relevant concentration variable for rationalizing the Seebeck coefficient data is c, the fraction of nontetrahedral vanadium ion sites which are polarons. The polarons interlay coordination number is 3. The average hopping distance varies by only 5% for 0 less than equivalent to x less than equivalent to 1. Comparison of experimental conductivities with sigma equals Ne**2a**2 beta nu //0c(1 minus c)**n** plus **1 exp minus beta W(c,x) suggests that n is near 3 and that the jump frequency nu //0 varies by nearly a factor of 3 over the composition range.