Effect on SmBa2Cu3Oy films of lattice strain induced by BaHfO3 nanorods

Abstract

BaMO3 (BMO, M=Zr, Sn, Hf, etc.) is well known to undergo self-organisation into many nanorods in a REBCO film grown by vapour phase epitaxy. However, REBCO experiences strain resulting from the BMO nanorods and this strain causes the superconducting properties to deteriorate. In this study, we prepared SmBCO films containing 16 vol% BaHfO3 (BHO) using a pulsed laser deposition method. Deposition was accomplished by using a low-temperature growth (LTG) technique to grow the films even at low substrate temperatures. By decreasing the substrate temperature, the number density of the BHO nanorods, which is estimated from the critical current density in magnetic fields and the irreversibility line, increased and their diameter decreased. The lattice strain exerted upon SmBCO and BHO could conveniently be evaluated by conventional X-ray diffraction owing to the substantial BHO content. This evaluation indicated that, as the substrate temperature decreased, the tensile strain exerted upon SmBCO decreased, whereas the compressive strain experienced by BHO increased. These results indicate that the effect of stress exercised by the narrow nanorods on REBCO is small. Our findings suggest LTG to be an effective technique to prepare REBCO films with a high number density of BMO nanorods owing to the small amount of stress induced by these nanorods.