Bulk superconductivity in both tetragonal and orthorhombic solid solutions of (${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${)}_2$${\mathrm{CuO}}_{4\mathrm{-}\mathrm{\delta }}$

Comparative measurements of low-field Meissner and shielding signals of both powder and sintered pellet samples of (${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${)}_2$ ${\mathrm{CuO}}_{4\mathrm{-}\mathrm{\delta }}$ have revealed that bulk superconductivity is present over a wide range of Sr composition, 0.0425≤x≤0.125, extending over the orthorhombic-to-tetragonal phase boundary at x≃0.105, except for a narrow anomaly region x=0.0625. Samples were prepared by three different methods through a combination of spray-drying or powder-mixing preparation with either slow cooling or quenching from the sintering temperature of 1100 °C down to 500 °C, at which oxygenation annealing was performed. Homogeneous solid solutions were obtained only for specimens prepared by spray drying and slow cooling. Dependences of the Meissner and shielding signals on the Sr content, on the intensity of magnetic field, and on the sample size were examined in terms of pinning effect and penetration depth.