Abstract: A corrosion resistant high temperature superconductor and a method of preparing said superconductors involving substitution of ions in the lattice to relieve stress and strain caused by mismatched bond lengths. Specific examples of such superconductors are Y.sub.1-y Ca.sub.y Ba.sub.2-y La.sub.y Cu.sub.3 O.sub.7-d where O<y<1.0 and O<d<1 and YBa.sub.2-y Sr.sub.y Cu.sub.3 O.sub.7-d where 0<y<2 and O<d<1. In YBa.sub.2 Cu.sub.3 O.sub.7-d structure, the internal stresses estimated from the difference between the bond valence sum and the formal oxidation state for Ba and Cu ions indicate that the Ba atom is too large for Cu--O cage at oxygen stoichiometric d=0 and too small at d=1. Therefore, the Ba (1.52 .ANG.) is substituted by La (1.27 .ANG.) and for keeping the same oxidation state of Cu as in the prototype material the Ca (1.12 .ANG.) equivalent to La replaces the Y (1.019 .ANG.).