The electronic and structural phase diagram of heavily doped ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$ (0.15≤x≤0.3) is reexamined. We demonstrate that the disappearance of superconductivity in ‘‘overdoped’’ ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$ is associated with an orthorhombic to tetragonal structural phase transition near x=0.2, implying a relationship between superconductivity and subtle structural change. The bulk superconducting phase is thus confined to a much narrower composition range than believed. A complete solid solution of La and Sr is observed in the composition range investigated.

• Received 6 January 1992

DOI:https://doi.org/10.1103/PhysRevLett.68.3777