BYZO Nanopancakes in HTS YBa2Cu3O7-δ Films: Effect on Critical Current Density and Nonlinear Microwave Response

Abstract

ABSTRACTWe have studied nanostructure, electric transport and microwave properties of HTS YBa2Cu3O7-δ films prepared by PLD on LaAlO3 single crystal substrates using targets doped with BaZrO3. Two essentially different types of nanoparticles are revealed by HREM: “nanopancakes” and “nanorods”. Tiny nanopancakes are 1-4 nm in ab-plane and only few atomic layers thick. Nanopancakes are surrounded with deformed area and numerous dislocations. Such nanoparticles seem to be responsible for jc enhancement. Nanopancakes evolve to much wider and longer nanorods at higher substrate temperatures and/or slower deposition. There are no dislocations around nanorods. Elastic strains are avoided due to slight inclination of the c-axis. Dislocations around nanopancakes are suggested to be additional flux pinning centers and retard thermally activated relaxation of the dislocation nanostructure.