Importance of low-angle grain boundaries inYBa2Cu3O7−δ coated conductors

Abstract

Over the past ten years the perception of grain boundaries inYBa2Cu3O7−δ conductors has changed greatly. They are now not a problem to be eliminated, but aninevitable and potentially favourable part of the material. This change has arisen as aconsequence of new manufacturing techniques which result in excellent grainalignment, reducing the spread of grain boundary misorientation angles. At thesame time there is considerable recent evidence which indicates that the variationof properties of grain boundaries with mismatch angle is more complex thana simple exponential decrease in critical current. This is due to the fact thatlow-angle grain boundaries represent a qualitatively different system to high-angleboundaries. The time is therefore right for a targeted review of research into low-angleYBa2Cu3O7−δ grainboundaries. This article does not purport to be a comprehensive review of the physics of grain boundaries asfound in YBa2Cu3O7−δ in general; for a broader overview we would recommend that the reader consult the comprehensivereview of Hilgenkamp and Mannhart (2002 Rev. Mod. Phys. 74 485). The purpose of thisarticle is to review the origin and properties of the low-angle grain boundaries found inYBa2Cu3O7−δ coated conductors both individually and as a collective system.