Superconductivity and temperature anomalies of the lattice properties of La(1.8)Ba(0.2)CuO(4-y) metal oxide

The specific heat, IR absorption spectra, and thermal expansion coefficient of La(1.8)Ba(0.2)CuO(4-y) superconductor are determined as a function of temperature. A discontinuity of specific heat and an anomaly of the thermal expansion coefficent are observed near the critical temperature, indicating that the superconducting properties of the compound are associated with a volume effect. A calculation is made of the temperature dependence of the upper critical magnetic field, Hc2, of a superconductor with a dielectric slot, Sigma, over part of the Fermi surface. It is shown that the Hc2(T) curve can differ significantly from the case Sigma=0, in agreement with experimental data.