COPPER WHISKER GROWTH FROM INSIDE SULFUR-DOPED YBA2CU3O7-X PELLETS

We report on the growth of Cu whiskers (10 mu m in linear transverse s ize) at the surface of a YBCO pellet, in a sulfur-rich atmosphere at a high synthesis temperature. Growth arises from inside the pellet sinc e there is no Cu in the surrounding atmosphere. We present the experim ental conditions and electron microscopic observations. We briefly pro pose a mechanism based on chemical considerations, in particular, a Cu reductive nucleation of the CuS phase at the surface of YBCO. Natural phenomena, laboratory findings, and computer simulation work (based o n an Eden model) support this interpretation. (C) 1995 Academic Press, Inc.