Crystal Growth and High-Pressure Effects of Bi-Based Superconducting Whiskers

Three growth methods were tested for producing high-transition temperature superconducting Bi$_2$Sr$_2$Ca$_{n-1}$Cu$_n$O$_{2n+4+{\delta}}$ whiskers, employing different ways to focus a compressive stress and size effect of the precursors. First, thermographic imaging was used to investigate thermal stress from temperature distribution in the precursors during growth annealing. To enhance thermal stress in the precursors, a thermal cycling method and an Ag-paste coating method were proposed and found to significantly accelerate the whisker growth. The use of pulverized precursors also promoted whisker growth, possibly due to contribution from the vapor-liquid-solid growth mechanism. The obtained whiskers revealed the typical composition, diffraction patterns, and superconducting properties of the Bi-2212 phase. The proposed methods were able to stably produce longer whiskers compared to the conventional method. Using the obtained whiskers, electrical transport measurements under high pressure were successfully performed at up to around 50 GPa.