Three growth methods
were tested for producing high-transition
temperature superconducting Bi
2
Sr
2
Ca
n
–1
Cu
n
O
2
n
+4+δ
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 a 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 up to around 50 GPa.