Microstructures and Superconducting Properties of BHO-doped SmBa₂Cu₃O_y Thin Films Grown by Changing the Growth Temperature using the PLD-LTG Technique

Abstract

REBa₂Cu₃O_y (RE: Rare Earth) is expected to be a promising superconducting material on the grounds that it has a high critical temperature (T_c). According to our previous work, it was reported that BaMO₃ (BMO, M=Zr, Sn, Hf, etc.) nanorod formation depends on the substrate temperature and volume fraction of BHO. We fabricated SmBa₂Cu₃O_y (SmBCO) films with 3.0 vol.% BaHfO₃ (BHO) nanorods using a pulsed laser deposition (PLD) method adopting a low-temperature growth (LTG) technique. Using the LTG technique, the lower temperature limit of c-axis orientation expands to the low-temperature region. However, the growth process of BHO has not yet been clarified. In this study, in order to clarify the growth mechanism of BHO nanorods, we changed the substrate temperature during the deposition process. As a result, the BHO number density decreased slowly as the film grew under increasingly warmer substrate temperatures. On the other hand, the BHO number density decreased dramatically under a sudden increase in substrate temperature. From transmission electron microscopic images, BHO nanorods were overgrown by the SmBCO near the film surface under increasing slowly substrate temperature. Both films showed high performance of J_c under a low magnetic field due to decreasing the matching field.