Structural and superconducting properties of ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$ as a function of Sr content

We have studied the structural and superconducting properties of ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ by neutron and x-ray powder diffraction, thermogravimetry, ac susceptibility, and dc magnetization. The kinetics of the synthesis reaction were studied in order to determine the optimum conditions for preparing single-phase samples. The room-temperature and low-temperature structural properties, as determined by neutron powder diffraction, are discussed in detail. By comparing the results of the neutron-diffraction and magnetic measurements, we conclude that superconductivity exists in both the orthorhombic and tetragonal phases. The thermodynamic conditions for the stability of the ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ phase are also investigated.