Temperature and composition dependence of the tetragonal-orthorhombic distortion in La sub (2-x) Sr sub x CuO (4-delta).

We have mapped the temperature and composition dependence of the tetragonal-orthorhombic phase transition temperature, t sub d, in the high-temperature superconductor, La sub (2- x) Sr sub x CuO (4-delta), using high-resolution powder x-ray diffraction and measurements of the thermal expansion. The maximum volume fraction of ideal diamagnetism occurs in the composition range where T sub d is approaching the superconducting transition. In the composition range x.0.20 where no orthorhombic distortion is observed above 12K, no bulk superconductivity is observed in La sub (2-x) Sr sub x CuO (4-delta).