Abstract
The thermal expansion properties of polycrystalline Bi2Sr2Ca1Cu2O8+x melt-processed bulk specimens, and Bi2Sr2Ca1Cu2O8+x monocore as well as multifilamentary round wires in Ag or Ag-alloy matrix have been investigated over the temperature range from -150 to 800 degrees C. Although the thermal expansion of Bi2Sr2Ca1Cu2O8+x is distinctly lower compared with Ag, the thermal expansion properties of the Bi2Sr2Ca1Cu2O8+x-Ag or AgNiMg-alloy composite conductors are essentially governed by the matrix material. The thermal expansion of the encountered oxide-dispersion-strengthened AgNiMg alloys is only slightly lower compared with that of pure Ag. Therefore the thermal expansion of all investigated Bi2Sr2Ca1Cu2O8+x-Ag or Ag-alloy composite wires was found to be close to that of pure Ag. The reason for this striking behaviour is shown to be related to a surprisingly low elastic modulus of the polycrystalline Bi-2212 wire cores of the order of 10 to a maximum 40 GPa.