The growth of superconducting whiskers of Bi2Sr2Ca~Cu2Ox is described. The whiskers are single-crystal, and show elastic behaviour, The superconducting transition temperature of the whiskers is near 75 K.
We have found in the course of the preparation of high temperature superconducting phases in the bismuth-strontium--calcium-copper oxide system [ 1,2 ] that superconducting crystals can grow in the form of thin long whiskers under certain conditions. These whiskers have many properties in common with more conventional metal whiskers, in particular their elasticity.
Superconducting whiskers were grown from a variety of starting mixtures of Bi203, SrCO3, CaCO3, and CuO by the usual powder sintering process. The powders were thoroughly mixed and ground, and calcined as powders in alumina or zirconia crucibles. Calcining was carried out in air at temperatures between 830 and 840°C for a period of 48 hours. The resultant product was re-ground, formed into a pellet, and sintered in air for another 24 to 48 hours at 830 to 840°C. The pellet was then oven-cooled, but at quite a large rate of temperature-decrease (about 500°C/h). Our best results for whisker formation were obtained with starting mixtures containing the metals in the ratio Bi: Sr: Ca: Cu = 4: 3: 3: 5, but other mixtures also resulted in whisker growth.
Growth of whiskers was observed both in the calcined powders, and on the sintered pellets. Inspection under a low powder microscope shows numerous