Thermal expansion of Bi2.2Sr1.8CaCu2Ox superconductor single crystals

Using a low-temperature stage X-ray diffractometer, we have investigated the temperature dependence of the lattice parameters of single crystal superconductors Bi₂Sr_1.8CaCu₂O_x. The experimental results show that (i) the lattice constants increase linearly with increasing temperature above about 100 K; (ii) thec-axis lattice parameter shows a kink in the superconducting transition region, while thea, b-axis parameters do not show any anomalous behavior in this region; (iii) botha, b, andc show negative thermal expansion coefficients below 40–50 K, which may be related to the characteristics of the Cu-O bond.