Low temperature synthesis and superconducting properties of polycrystalline T′-(La,Sm)2CuO4

La2−xSmxCuO4+δ with the Nd2CuO4 structure was synthesized by precipitation from fused alkaline hydroxide, CsOH, at 400 °C. The as-sintered polycrystalline samples showed no diamagnetic signal, but after post-annealing in vacuum of ≈10−8 atm at 650-700 °C, the samples with x = 0.1 and 0.3 exhibited superconductivity at Tc on = 25 K. The volume fraction of the superconducting phase estimated from the slope of the Zero-Field-Cooled magnetization data was over 30% for x = 0.3, which confirmed that the La1.7Sm0.3CuO4+δ is a bulk superconductor.