Critical point phase transformations applied to ceramic superconductors

A second order phase transformation in dielectric ceramic superconductors is shown to relate jumps in physical properties to the ratio of state variables i.e. the phase boundary, near the critical point. The major jumps in specific heat, compressibility, permittivity, permeability and spinodal composition curvature between the normal ad superconducting phases, are found from the continuity of the entropy, volume, electro-magnetic fields (with zero fields) and chemical equilibrium. The thermal expansion, pyroelectric effects and the piezo electro-magnetic effects are important differences between ceramic and metallic superconductors. The most important conclusions from experimental measurements are that the oxygen order/disorder transformation thermodynamically mandates that only metastable compositions in the metal oxide quaternary are possible, so absolute stability of the Y/sub 1/Ba/sub 2/Cu/sub 3/0/sub 7-δ/ system may never be achieved. The miscibility gap which controls the superconducting transformation has not been optimized nor fully exploited. In addition, measurements suggest that the lattice plays a minor role in the superconductor transformation while the magnetoelectric jump may be related to the jump in permeability i.e. Miessner effect, and the jump im permittivity. An explicit criteria to suggest other superconductor systems is given