Thermal Expansion and Superconductivity in Alkali Metal‐ and Silver‐doped BiSrCaCuO System

Samples with the nominal composition Bi 2 Sr 2 CaCu 2 O y with na doped at the Ca site and K doped at the Sr site are prepared by solid state reaction method. From the X‐ray diffraction data it is found that all the the samples have exhibited a single phase 2212. The D.C. electrical resistivity data show that for Na‐doped samples the T c (zero) varies from 80 K to 85 K and for K‐doped samples it is from 79 K to 82 K. The loss of oxygen from these samples around 400°C was confirmed by high temperature dilatometry. The variation of the thermal expansion coefficient (“α”) with temperature for different alkali dopings are discussed. Also the samples with the nominal composition Bi 4 Sr 3 Ca 3 Cu 4− x Ag x O y (with x = 0, 0.1, 0.2, 0.3) were studied.