Superconductivity in bulk T′-(La,Sm)2CuO4 prepared via a molten alkaline hydroxide route

We have synthesized La2−xSmxCuO4 (0 ⩽ x ⩽ 2.0) with the Nd2CuO4 structure via a molten alkaline hydroxide route at temperatures as low as 400–480 °C. After reduction heat treatment in vacuum at 600–750 °C for removal of excess oxygen atoms at the interstitial apical site, superconductivity with Tc = 20–24 K was observed in the samples with x = 0.05–1.0. The superconducting volume fraction is nearly 100% for x = 0.3–0.7. Our results demonstrate that La2−xSmxCuO4 with no nominal carrier doping is a bulk superconductor.

► Low-temperature synthesis of superconducting La2–xSmxCuO4 with the Nd2CuO4 structure via a molten alkaline hydroxide route.
► Superconductivity with Tc = 20–24 K was observed for x = 0.05–1.0 after reduction heat treatments for the removal of interstitial apical oxygen atoms.
► The results present clear evidence of bulk superconductivity in the nominally undoped La2–xSmxCuO4 system.