Application of neutron diffraction to the characterization of residual thermal strains in YBa2Cu3O7−δ/Ag

Abstract

Additions of silver (Ag) have been reported to improve the mechanical properties of high-temperature superconductor by YBa2Cu3O7−δ (abbreviated YBCO). However, during fabrication of YBCO/Ag composites, differential thermal expansion upon cooling can lead to potentially troublesome residual stresses. The Intense Pulsed Neutron Source and General Purpose Powder Diffractometer at Argonne National Laboratory were used to show that neutron diffraction techniques can be applied to YBCO/Ag composites to measure bulk residual strains in the constituent parts, and to determine the effect of Ag on stoichiometry (and thus on the critical current density). We have observed residual tensile strains in Ag as a function of crystallographic direction; three strains range from as high as 0.085% in 15% Ag samples to as low as about 0.02% in a 30% Ag sample. Compressive strains in the YBCO (111) crystallographic direction were approximated by correcting for the diffraction peak shift due to changes in stoichiometry with varying Ag content. The estimated compressive-strain values vary from 0.04% (15% Ag) to 0.09% (20% Ag) to 0.01% (30% Ag), with an uncertainty of about 0.03%. The presence of significant average tensile strain in the Ag, particularly for 15% and 20% Ag samples, indicates good interface bonding between YBCO and Ag.