  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.
