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.

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We are currently developing an external-heating-type superconducting magnesium diboride (MgB₂)-level sensor for a large liquid hydrogen tank as one of the basic technologies for the marine transportation of liquid hydrogen. Optimization of the sensor performance and effect of sensor length on thermal response were previously reported. However, the performance variation of the MgB₂ sensor caused by individual differences in the wire rod has not yet been clarified. In this study, we developed a simultaneous calibration system for five MgB₂-level sensors, and examined the level-detecting characteristics of five 500-mm-long MgB₂-level sensors. It was found that the maximum performance variation of the MgB₂ sensors was about 2% for the full scale of the sensor length, although the four fifth sensors indicated the same results. Therefore, the performance variation in MgB₂ sensors caused by individual differences in the wire rods was minimal.

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