Thermodynamics of the Superconducting Phase Transition on High T_c Superconductor RBa₂Cu₃O_y

The property of superconducting phase transition of the high Tc superconductor RBa₂Cu₃O_y (R:most rare earth elements) was investigated. The conclusion was drawn that the phase transition changed from first order in magnetic field to second order in non-magnetic field. The representation of the Gibbs free energy of the superconductor RBa₂Cu₃O_y at the superconducting-normla state transition in non-magnetic field was derived.