SUPERCONDUCTOR-INSULATOR TRANSITION IN YBA2CU3-XNBXO7 MATERIAL

We have synthesized and investigated YBa2Cu3-xNbxO7 material in the ra nge of Nb contents 0 < x < 0.9. For small x < 0.21 materials were foun d to be superconductive at similar to 90 K. At x similar to 0.21 there occurred the superconductor-insulator transition. Nb added to YBa2Cu3 O7 (123) results in a formation of dielectric inclusions YBa2NbO6, whi ch dilute the superconducting grains. In the insulating state of mater ial conduction is determined by Variable Range Hopping (VRH) Mechanism . The localization radius and the density of states at the Fermi level were estimated.