Structure and transport properties of YBCO thin films and single crystals

Abstract

Mechanisms of nucleation and growth of YBCO thin films and their real microstructures are investigated and discussed regarding to effective pinning sites and critical current densities. Edge dislocations with Burgers vector b=a[100] on low angle tilt grain boundaries appeared to be served the strongest pins providing critical current densities Jc(77 K)≳5×106 A/cm2. Edge dislocation density in thin YBCO films grown at high substrate temperatures by island mechanism exceeds 1011 cm−2 saving quasi‐single‐crystalline film structure with average misorientation angle between islands in ab‐plane about 4°. Direct measurements of transport critical current density and resistive state for YBCO single crystals have been performed using thin microbridges. Critical current densities more than 105 A/cm2 at 82 K have been observed. It was shown flux flow phenomena are essentially different for thin films and single crystals. Peculiarities of resistive state for thin films in magnetic fields H∥c appeared to be connected ...