Thermal Expansion Coefficients of High-Tc Superconductors

Abstract

High-T _c superconducting oxides were confirmed to have much higher thermal expansion coefficients than various substrate materials. The difference in thermal expansion between superconductor and substrate materials corresponded well with the crack size formed in the film. Thermal expansion of Ba₂YCu₃O_7-δ abruptly changes at about 350°C and 650°C, which reflects the change of oxygen concentration and the phase transition, respectively. The expansion pattern varied considerably by the substitution of yttrium by ytterbium, suggesting a difference in the kinetics of oxygen uptake and secession between the two superconductors.