Strain-controlled critical temperature in REBa(2)Cu(3)O(y)-coated conductors

Recently, we succeeded in detwinning REBa(2)Cu(3)O(7) (RE123, RE = rare-earth elements)-coated conductors by annealing under an external uniaxial strain. Using the untwinned RE123 tapes, the uniaxial-strain dependencies of the critical temperature T(c) along the a and b crystal axes were investigated over a wide strain region from compression to tension. We found that the strain dependencies of T(c) for the a and b axes obey a power law but exhibit opposite slopes. In particular, the maximum value of T(c) is obtained when the CuO(2) plane becomes a square, and its lattice constant is close to 0.385 nm. It is suggested that a tetragonal structure with a ≈ 0.385 nm is the optimum condition for a high critical temperature in high-T(c) cuprates.